Fuller’s Earth - ACS
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February 2013 Teacher's Guide
Table of Contents
About the Guide 3
Student Questions (from the articles) 4
Answers to Student Questions (from the articles) 6
ChemMatters Puzzle: Su-Chem-Du 10
Answers to the ChemMatters Puzzle 12
NSES Correlation 13
Anticipation Guides 14
Fighting Cancer with Lasers 15
Brand-Name vs. Generic Drugs: What’s the Difference? 16
Sniffing Out Cancer 17
Drivers, Start Your Electric Engines! 18
Is Your Car a Living Thing? 19
Reading Strategies 20
Fighting Cancer with Lasers 21
Brand-Name vs. Generic Drugs: What’s the Difference? 22
Sniffing Out Cancer 23
Drivers, Start Your Electric Engines! 24
Is Your Car a Living Thing? 25
Fighting Cancer with Lasers 26
Background Information (teacher information) 26
Connections to Chemistry Concepts (for correlation to course curriculum) 43
Possible Student Misconceptions (to aid teacher in addressing misconceptions) 43
Anticipating Student Questions (answers to questions students might ask in class) 44
In-class Activities (lesson ideas, including labs & demonstrations) 46
Out-of-class Activities and Projects (student research, class projects) 47
References (non-Web-based information sources) 48
Web sites for Additional Information (Web-based information sources) 50
Brand-Name vs. Generic Drugs: What’s The Difference? 53
Background Information (teacher information) 53
Connections to Chemistry Concepts (for correlation to course curriculum) 63
Possible Student Misconceptions (to aid teacher in addressing misconceptions) 64
Anticipating Student Questions (answers to questions students might ask in class) 64
In-class Activities (lesson ideas, including labs & demonstrations) 64
Out-of-class Activities and Projects (student research, class projects) 65
References (non-Web-based information sources) 66
Web sites for Additional Information (Web-based information sources) 67
More Web sites on Teacher Information and Lesson Plans (sites geared specifically to teachers) 68
Sniffing Out Cancer 70
Background Information (teacher information) 70
Connections to Chemistry Concepts (for correlation to course curriculum) 77
Possible Student Misconceptions (to aid teacher in addressing misconceptions) 78
Anticipating Student Questions (answers to questions students might ask in class) 78
In-class Activities (lesson ideas, including labs & demonstrations) 80
Out-of-class Activities and Projects (student research, class projects) 81
References (non-Web-based information sources) 81
Web sites for Additional Information (Web-based information sources) 82
Drivers, Start Your Electric Engines! 86
Background Information (teacher information) 86
Connections to Chemistry Concepts (for correlation to course curriculum) 99
Possible Student Misconceptions (to aid teacher in addressing misconceptions) 100
Anticipating Student Questions (answers to questions students might ask in class) 100
In-class Activities (lesson ideas, including labs & demonstrations) 102
Out-of-class Activities and Projects (student research, class projects) 104
References (non-Web-based information sources) 105
Web sites for Additional Information (Web-based information sources) 107
More Web sites on Teacher Information and Lesson Plans 110
Is Your Car a Living Thing? 111
Background Information (teacher information) 111
Connections to Chemistry Concepts (for correlation to course curriculum) 122
Possible Student Misconceptions (to aid teacher in addressing misconceptions) 122
Anticipating Student Questions (answers to questions students might ask in class) 123
In-class Activities (lesson ideas, including labs & demonstrations) 123
Out-of-class Activities and Projects (student research, class projects) 124
References (non-Web-based information sources) 125
Web sites for Additional Information (Web-based information sources) 126
About the Guide
Teacher’s Guide editors William Bleam, Donald McKinney, Ronald Tempest, and Erica K. Jacobsen created the Teacher’s Guide article material. E-mail: bbleam@
Susan Cooper prepared the national science education content, anticipation guides, and reading guides.
David Olney created the puzzle.
E-mail: djolney@
Patrice Pages, ChemMatters editor, coordinated production and prepared the Microsoft Word and PDF versions of the Teacher’s Guide. E-mail: chemmatters@
Articles from past issues of ChemMatters can be accessed from a CD that is available from the American Chemical Society for $30. The CD contains all ChemMatters issues from February 1983 to April 2008.
The ChemMatters CD includes an Index that covers all issues from February 1983 to April 2008.
The ChemMatters CD can be purchased by calling 1-800-227-5558.
Purchase information can be found online at chemmatters
Student Questions
(from the articles)
Fighting Cancer with Lasers
1. What medical tool did doctors use to determine the problem causing Chris’s pain?
2. What is the name of the type of tumor found in his thigh?
3. Was the tumor cancerous?
4. What two medical tools do doctors use to treat the tumor?
5. What role does the needle play in destroying the tumor?
6. Was the operation difficult or complicated?
7. What is the meaning of the acronym LASER?
8. Name three properties of laser light.
9. Name the two processes involved in generating laser light. Explain each.
10. Name two advantages and two disadvantages of using lasers for treating cancers.
Brand-Name vs. Generic Drugs: What’s the Difference?
1. By law, what must be the same for a brand-name drug and its generic equivalent? What can be different?
2. What is the role of the active ingredients in a drug?
3. What can affect the solubility of a drug, or the way it dissolves in the body?
4. Explain why a hot solvent dissolves a solid faster.
5. What does a concentration–time graph (or blood concentration curve) of a drug show?
6. What is the U.S. Food and Drug Administration rule regarding the concentration–time graphs for a brand-name drug and its generic equivalent?
Sniffing Out Cancer
11. What is a Volatile Organic Compound (VOC)?
12. For people with tumors, what body products can carry or contain VOCs?
13. Volatility of an organic compound depends on its vapor pressure. What is meant by vapor pressure?
14. Describe the chemical properties of reactive oxygen species and how they are related to cancer.
15. What is the relationship between VOCs and reactive oxygen species?
16. Give two advantages when choosing dogs over chemical instrumentation for cancer detection?
17. What types of cancer are dogs capable of detecting?
18. What two biological products of the body are sniffed by dogs in detecting cancer?
Drivers, Start Your Electric Engines!
1. Name two advantages for the electric car.
2. For what use is the electric car primarily designed?
3. What helps to minimize “range anxiety”?
4. True or false: The first electric car was the Nissan Leaf. Explain your answer.
5. What is the chemical term for the process that happens at the lead plate in a lead-acid battery? Describe this process.
6. What happens when a lead-acid battery recharges?
7. What type of battery is used in today’s electric cars?
8. Describe the composition of the two electrodes in a lithium-ion battery.
9. List four advantages that lithium-ion batteries have over lead-acid batteries.
10. List three disadvantages of using electric cars.
Is Your Car a Living Thing?
1. Name three chemical compounds mentioned in the article that are broken down in either a car or a human.
2. Name and describe the process that separates the components of petroleum (crude oil).
3. What is the difference between hydrocarbons and carbohydrates?
4. What chemicals in the body are responsible for much of the breakdown of food in the digestive process?
5. What are the common products of both cellular respiration and combustion?
6. Where in human cells is energy produced?
7. In what part of a car is the majority of the energy produced?
8. Name the three chemical elements that are used as catalysts in the catalytic converters of automobiles.
Answers to Student Questions
(from the articles)
Fighting Cancer with Lasers
1. What medical tool did doctors use to determine the problem causing Chris’s pain?
The medical tool used by doctors to determine the origin of Chris’s pain was the computed tomography scan, or CT scan.
2. What is the name of the type of tumor found in his thigh?
The tumor in Chris’s thigh was an osteoid osteoma.
3. Was the tumor cancerous?
Luckily, Chris’s tumor was not cancerous; it was benign.
4. What two medical tools do doctors use to treat the tumor?
Doctors typically use radio waves of lasers to treat tumors of this type.
5. What role does the needle play in destroying the tumor?
Doctors insert the needle into the center of the tumor; then they insert an optic fiber into the needle. The fiber is used to direct the intense light/heat of the laser to the center of the tumor.
6. Was the operation difficult or complicated?
Although Chris needed general anesthesia, the operation itself only took an hour, and Chris “... went home the same day and, within a short period of time, he was able to walk and resume his daily activities.” In short, the operation seemed pretty easy (although it’s still surgery and it’s still scary).
7. What is the meaning of the acronym LASER?
The acronym LASER means “Light Amplification by Stimulated Emission of Radiation”.
8. Name three properties of laser light.
Laser light:
a. is focused in a narrow beam,
b. has one specific wavelength,
c. is very intense.
9. Name the two processes involved in generating laser light. Explain each.
The two processes in generating laser light are stimulated emission and light amplification.
a. Stimulated emission involves incoming light causing atoms within the laser to emit light on their own. These atoms are bombarded with flashes of light or electrical discharges. This causes electrons within the atoms to absorb energy and jump to higher energy states (excited states). When these electrons from excited states return to their original ground states, they release photons of light. These photons then stimulate other electrons in excited states to jump back down to their ground state, thereby emitting more photons, all of which travel in the same direction.
b. Light amplification occurs when the photons of light travel back and forth within the laser medium reflecting off the two mirrors. As they bounce back and forth between the mirrors, they stimulate more and more excited electrons to return to their ground states, thus emitting even more photons. Eventually the light wave leaves the laser medium through the partially-coated mirror, creating the laser beam.
10. Name two advantages and two disadvantages of using lasers for treating cancers.
Two advantages of using laser for treating tumors are:
a. The laser can be used to repair small parts or surfaces of the body, much like a scalpel,
b. The heat from laser light actually helps to sterilize wounds.
The disadvantages of using laser light for tumor treatment are:
a. their high price,
b. the bulkiness of the equipment to generate the laser beams,
c. the need for training and precautions for medical staff using the laser.
Brand-Name vs. Generic Drugs: What’s the Difference?
1. By law, what must be the same for a brand-name drug and its generic equivalent? What can be different?
By law, a brand-name drug and its generic equivalent must have the same active ingredients. The inactive ingredients, such as pigments, flavoring, and binders can differ.
2. What is the role of the active ingredients in a drug?
Active ingredients are the ingredients that cause a drug’s effect, such as pain relief or anti-nausea.
3. What can affect the solubility of a drug, or the way it dissolves in the body?
Inactive ingredients in a drug can affect the way a drug dissolves in the body. Temperature also affects solubility. Pharmaceutical companies adjust their drugs so they dissolve at body temperature.
4. Explain why a hot solvent dissolves a solid faster.
Hot solvents dissolve solids faster because their molecules move faster than cold ones. Increased molecular motion competes with the attraction between the molecules in the solute and tends to make them come apart more easily. Increased molecular motion also causes more solvent molecules to interact with solute molecules and pull on them with more force, which makes them dissolve more.
5. What does a concentration–time graph (or blood concentration curve) of a drug show?
A concentration–time graph of a drug shows the concentration of a drug in the bloodstream at regular time intervals.
6. What is the U.S. Food and Drug Administration rule regarding the concentration–time graphs for a brand-name drug and its generic equivalent?
The U.S. Food and Drug Administration rule states that when the concentration–time graphs for a brand-name drug and its generic equivalent are compared, the difference between them should not be larger than 20% of the brand-name drug’s curve.
Sniffing Out Cancer
1. What is a Volatile Organic Compound (VOC)?
A volatile organic compound is a molecule that evaporates or sublimates from a liquid or solid phase of the same substance.
2. For people with tumors, what body products can carry or contain VOCs?
Some of the body products containing VOCs include exhaled breath, urine, and stool, among others.
3. Volatility of an organic compound depends on its vapor pressure. What is meant by vapor pressure?
“Vapor pressure is the pressure at which vaporized molecules reach equilibrium with the solid or liquid phase of the same substance in a closed system.”
4. Describe the chemical properties of reactive oxygen species and how they are related to cancer.
Reactive oxygen species are molecules with unpaired valence electrons that make them highly reactive with surrounding biological materials. If reactive oxygen species are in excess, perhaps because of a deficiency of antioxidant molecules that keep reactive oxygen species in check, then they can damage DNA and healthy cell tissue. This damaging process is known as oxidative stress and is known to be a precursor of cancer.
5. What is the relationship between VOCs and reactive oxygen species?
Under oxidative stress as outlined in answer #4, “reactive oxygen species oxidize fats in cell membranes, resulting in increased emissions of VOCs ..”. Dozens of specific VOCs have been linked to various types of cancer. Tumors produce changes in not just one type of VOC, but many.
6. Give two advantages when choosing dogs over chemical instrumentation for cancer detection?
A dog’s nose is a highly efficient chemical sensor, ready-made to sniff cancer VOCs. Second, a dog can detect a cancer through smelling VOCs without needing to know the specific chemical or chemicals present in the vapor. A chemical instrument can only be designed when a specific chemical to be detected is known.
7. What types of cancer are dogs capable of detecting?
Dogs that are trained can detect skin, breast, lung, prostate, colon, bladder, and ovarian cancer.
8. What two biological products of the body are sniffed by dogs in detecting cancer?
The two biological products sniffed for cancer-produced VOCs are urine and exhaled air.
Drivers, Start Your Electric Engines!
1. Name two advantages for the electric car.
Advantages of the electric car are:
a. Fewer moving parts, so less maintenance is required,
b. Brakes, part of the energy-recovery system, last much longer than ordinary car brakes.
2. For what use is the electric car primarily designed?
City driving is the main use for which electric cars are designed. This includes commuting, running local errands and trips around town.
3. What helps to minimize “range anxiety”?
Onboard computers in electric cars indicate level of charge and remaining range of travel, making it less likely that you will allow the battery to run down, minimizing “range anxiety”.
4. True or false: The first electric car was the Nissan Leaf. Explain your answer.
This statement is false. Electric cars were built as early as 1828, and had become prevalent in the 1900s, until improvements in the gasoline-powered car gave it dominance.
5. What is the chemical term for the process that happens at the lead plate in a lead-acid battery? Describe this process.
Oxidation occurs at the lead plate in the lead-acid battery. This process involves the loss of electrons from the lead plate as it reacts to form lead(II) sulfate.
6. What happens when a lead-acid battery recharges?
Recharging a lead-acid battery involves pumping electrons into the battery from an outside source. This causes the oxidation of lead(II) to lead(IV), releasing two electrons in the process.
7. What type of battery is used in today’s electric cars?
Today’s electric cars (unlike those of the 1900s, which used lead-acid batteries) use lithium-ion batteries.
8. Describe the composition of the two electrodes in a lithium-ion battery.
The cathode (the positive terminal) is made of “a type of layered lithium oxide, such as lithium cobalt oxide (LiCoO2)”, while the “negative electrode, or anode, is made of graphite—a form of pure carbon.
9. List four advantages that lithium-ion batteries have over lead-acid batteries.
Four advantages of lithium-ion batteries over lead-acid batteries:
a. They’re much lighter (think atomic weights: Li, 7; Pb, 207)
b. Lithium is much more reactive than lead, providing a higher charge density, 6:1 over lead.
c. Lithium-ion batteries hold a charge much longer than lead-acid batteries. They only lose 5% of their charge per month.
d. They have no “memory effect”, so they can be recharged at any level of charge.
10. List three disadvantages of using electric cars.
Three disadvantages of electric cars:
a. Their relatively short range of travel
b. Their high price
c. Their contribution to pollution, since the electricity they use for recharging is generated by burning coal.
Is Your Car a Living Thing?
1. Name three chemical compounds mentioned in the article that are broken down in either a car or a human.
There are multiple possible answers here, but the most obvious are the hydrocarbons that make up gasoline or the basic food nutrients—fats, carbohydrates or proteins. Other compounds mentioned include glucose, adenosine diphosphate or adenosine triphosphate.
2. Name and describe the process that separates the components of petroleum (crude oil).
The process to separate crude oil is called fractional distillation, a physical process that depends on the fact that each hydrocarbon component in crude oil has a unique (or nearly unique) boiling point. The petroleum is heated and each component vaporizes at its own temperature and is then condensed into liquid form. The liquid components are then remixed in desired proportions to form fuels like gasoline.
3. What is the difference between hydrocarbons and carbohydrates?
Both are considered organic compounds, but hydrocarbons are made up only hydrogen and oxygen while carbohydrates contain carbon, hydrogen and oxygen.
4. What chemicals in the body are responsible for much of the breakdown of food in the digestive process?
The article points to enzymes as the chemicals responsible for breaking down food into nutrients that can be used by the body
5. What are the common products of both cellular respiration and combustion?
In both processes oxygen is combined with a food or fuel to produce carbon dioxide and water.
6. Where in human cells is energy produced?
Cells have organelles called mitochondria. Energy is produced in these mitochondria.
7. In what part of a car is the majority of the energy produced?
In the cylinders of a car, gasoline vapor and oxygen are mixed and the mixture is ignited by a spark from the spark plug. The combustion of the fuel creates energy to move the car.
8. Name the three chemical elements that are used as catalysts in the catalytic converters of automobiles
The three elements used for catalytic converters listed in the article are platinum, palladium and rhodium.
ChemMatters Puzzle: Su-Chem-Du
Here’s a variation of a SUDOKU puzzle that needs some chemical knowledge as well as logic to solve.
1. Instead of numbers, we’re using nine letters in the grid: alphabetically they are C D E I N O R T and U.
Note that five of those letters are one-letter symbols of an element, namely C,I,N,O, and U,.
2. The more letters in the grid at the start, the easier its solution. We’re providing several of the letters
directly and 14 more can come from clues below. Any box in the grid with a number has as its letter one
of our five elements. The clue should help you zero in on the proper one.
3. Once you’ve answered as many clues as you can, proceed to solve the Sudoku grid. Remember that any
given letter must appear exactly ONCE in each row, column, and 3x3 square.
At any time you can go back to identify any remaining clues.
4. When finished, the letters in the top row complete this phrase: “In REDOX, the gaining of electrons is…”
| | |D |U | |T |
| | | | |5 | |
|Physical Science Standard A: necessary to do | |( | | | |
|scientific inquiry. | | | | | |
|Physical Science Standard A: about scientific |( |( |( |( |( |
|inquiry. | | | | | |
|Physical Science Standard B: of the structure | |( |( | |( |
|and properties of matter. | | | | | |
|Physical Science Standard B: of chemical | |( | |( |( |
|reactions. | | | | | |
|Life Science Standard C: of matter, energy, and| | | | |( |
|organization in living systems. | | | | | |
|Science and Technology Standard E: about |( |( |( |( |( |
|science and technology. | | | | | |
|Science in Personal and Social Perspectives |( |( |( | |( |
|Standard F: of personal and community health. | | | | | |
|Science in Personal and Social Perspectives |( |( |( |( | |
|Standard F: of science and technology in local,| | | | | |
|national, and global challenges. | | | | | |
|History and Nature of Science Standard G: of | | |( | | |
|science as a human endeavor. | | | | | |
|History and Nature of Science Standard G: of | |( |( | | |
|the nature of scientific knowledge | | | | | |
|History and Nature of Science Standard G: of | | |( |( | |
|historical perspectives. | | | | | |
Anticipation Guides
Anticipation guides help engage students by activating prior knowledge and stimulating student interest before reading. If class time permits, discuss students’ responses to each statement before reading each article. As they read, students should look for evidence supporting or refuting their initial responses.
Directions for all Anticipation Guides: Before reading, in the first column, write “A” or “D” indicating your agreement or disagreement with each statement. As you read, compare your opinions with information from the article. In the space under each statement, cite information from the article that supports or refutes your original ideas.
Fighting Cancer with Lasers
Directions: Before reading, in the first column, write “A” or “D” indicating your agreement or disagreement with each statement. As you read, compare your opinions with information from the article. In the space under each statement, cite information from the article that supports or refutes your original ideas.
|Me |Text |Statement |
| | |Tumors smaller than a marble can cause severe, sharp pain. |
| | |Laser surgery involves aiming a laser beam at the tumor to destroy it. |
| | |The term LASER is an acronym. |
| | |Light from a laser has many wavelengths. |
| | |Lasers have mirrors inside. |
| | |Electrons emit photons of light when they become excited. |
| | |Lasers are already used to treat harmful cancers such as liver cancer. |
| | |Laser surgery has less risk of infection and less pain. |
Brand-Name vs. Generic Drugs: What’s the Difference?
Directions: Before reading, in the first column, write “A” or “D” indicating your agreement or disagreement with each statement. As you read, compare your opinions with information from the article. In the space under each statement, cite information from the article that supports or refutes your original ideas.
|Me |Text |Statement |
| | |The U.S. FDA must regulate generic drugs. |
| | |Some people react better to generic drugs than to brand-name drugs. |
| | |By law, generic drugs and brand-name drugs must have exactly the same ingredients. |
| | |Both your stomach and your small intestine have acidic environments. |
| | |One significant way generics may differ from brand-name drugs is the amount of time it takes to dissolve in the body. |
| | |Switching from a brand-name to a generic drug is more risky than switching from one generic drug to another generic |
| | |drug. |
| | |No matter what the drug, all generic and brand-name drugs must be within 20% of each other on the concentration-time |
| | |graph for the drug product. |
| | |By far, generic drugs are more dangerous than brand-name drugs. |
| | |If one epileptic patient has a seizure after taking a drug, that drug cannot be sold any more. |
Sniffing Out Cancer
Directions: Before reading, in the first column, write “A” or “D” indicating your agreement or disagreement with each statement. As you read, compare your opinions with information from the article. In the space under each statement, cite information from the article that supports or refutes your original ideas.
|Me |Text |Statement |
| | |A report of a dog alerting his owner to a malignant melanoma was first published in 2002. |
| | |Vapor pressure depends on intermolecular forces. |
| | |Cancerous cells produce different concentrations of volatile organic compounds (VOCs) than healthy cells do. |
| | |A dog’s sense of smell is up to 100,000 times better than a human’s sense of smell. |
| | |Cigarette smoke interferes with a dog’s ability to detect lung cancer in a patient’s breath. |
| | |Researchers need to know what chemical they are looking for before they can train dogs to detect cancer-related smells. |
| | |Artificial noses are being developed that will eventually take over the work of dogs in detecting cancer in human |
| | |patients. |
| | |All VOCs in our environment are harmful to human beings. |
Drivers, Start Your Electric Engines!
Directions: Before reading, in the first column, write “A” or “D” indicating your agreement or disagreement with each statement. As you read, compare your opinions with information from the article. In the space under each statement, cite information from the article that supports or refutes your original ideas.
|Me |Text |Statement |
| | |Electric cars require much less maintenance than cars with internal combustion engines. |
| | |Electric cars in use today require 220-volt charging stations. |
| | |Today’s electric cars can travel about 400 miles before being recharged. |
| | |Electric cars were available in the early 20th century. |
| | |Lead-acid batteries can be recharged indefinitely. |
| | |Lead-acid batteries are found in today’s golf carts and gasoline-fueled cars. |
| | |Lithium batteries were not developed until the late 20th century. |
| | |Lithium-ion batteries are much lighter than lead-acid batteries, and they can store much more energy per kilogram than |
| | |lead-acid batteries. |
Is Your Car a Living Thing?
Directions: Before reading, in the first column, write “A” or “D” indicating your agreement or disagreement with each statement. As you read, compare your opinions with information from the article. In the space under each statement, cite information from the article that supports or refutes your original ideas.
|Me |Text |Statement |
| | |The only similarity between a car and a living organism is that a car uses energy. |
| | |The most common internal combustion engine has two steps that occur in each cylinder. |
| | |On average, between 10 and 20 mitochondria are found in each cell of a human body. |
| | |Mitochondria convert sugar to energy in four steps. |
| | |A person releases energy much faster than a car. |
| | |Catalytic converters have a large surface area and a catalyst, both of which speed up reaction rates. |
| | |Before entering the catalytic converter, the main pollutants in automobile exhaust are carbon monoxide, unburned |
| | |hydrocarbons, and nitrogen oxides. |
| | |Charles’s Law describes how the heat produced in a car engine makes the gases expand very rapidly. |
Reading Strategies
These matrices and organizers are provided to help students locate and analyze information from the articles. Student understanding will be enhanced when they explore and evaluate the information themselves, with input from the teacher if students are struggling. Encourage students to use their own words and avoid copying entire sentences from the articles. The use of bullets helps them do this. If you use these reading strategies to evaluate student performance, you may want to develop a grading rubric such as the one below.
|Score |Description |Evidence |
|4 |Excellent |Complete; details provided; demonstrates deep understanding. |
|3 |Good |Complete; few details provided; demonstrates some understanding. |
|2 |Fair |Incomplete; few details provided; some misconceptions evident. |
|1 |Poor |Very incomplete; no details provided; many misconceptions evident. |
|0 |Not acceptable |So incomplete that no judgment can be made about student understanding |
Teaching Strategies:
1. Links to Common Core State Standards: There are several opportunities to compare alternatives in this issue of ChemMatters. For example, you might ask students to take sides and find support for one of the following:
a. Using brand-name vs. generic drugs
b. Driving electric cars vs. cars with internal combustion engines
2. To help students engage with the text, ask students what questions they still have about the articles.
3. Vocabulary that may be new to students:
a. VOCs
b. Internal combustion engine
4. Important chemistry concepts that will be reinforced in this issue:
a. Reaction rate
b. Oxidation and reduction
Fighting Cancer with Lasers
Directions: As you read the article, describe how tumors are treated with lasers.
|Detection | |
|Locating tumor during surgery | |
|Directing laser into tumor | |
|Laser energy production | |
|Future uses of lasers in removing| |
|tumors | |
|Advantages of laser surgery | |
|Disadvantages of laser surgery | |
Brand-Name vs. Generic Drugs: What’s the Difference?
Directions: As you read, compare brand-name and generic drugs using the chart below.
|Brand-Name Drugs |Generic Drugs |
| | |
|Similarities |
Sniffing Out Cancer
Directions: As you read, describe they VOCs produced in cancer cells, then compare how dogs and machines can detect cancer in humans.
|VOCs |What are they? |How are VOCs produced by cancer cells different from those|
| | |produced by normal cells? |
| |Dogs |Artificial Noses |
|Advantages | | |
|Cancer detection | | |
|Future use in cancer | | |
|detection | | |
Drivers, Start Your Electric Engines!
Directions: As you read, compare lead-acid and lithium-ion batteries using the chart below.
| |Lead-Acid Battery |Lithium-ion Battery |
|When were they developed? | | |
|What chemicals are | | |
|involved? | | |
|How do they work? | | |
|What are the electrodes | | |
|made of? | | |
|Where are they used? | | |
|Compare the reactivity of | | |
|the metals involved. | | |
Is Your Car a Living Thing?
Directions: As you read, compare the chemical processes in you and a car.
|Process |You |A car |
|Digestion | | |
|Energy generation | | |
|Cleaning | | |
Fighting Cancer with Lasers
Background Information
(teacher information)
More on the history of lasers
The concept of the laser was first brought forth by Albert Einstein in 1917. His work seemed to always focus on light (no pun intended), and the idea of the laser was just a small piece of his studies. He theorized about stimulated emission of radiation, saying that if there were a large number of energized atoms each ready to emit a photon at a random time in a random direction, and if a stray photon happened to pass by, the energized atoms would be stimulated by its presence to emit their photons early. These new photons, he said, would have the same direction and same frequency as the original “trigger” photon. Repeating this process with more and more “stray” photons with each pass would result in laser light.
Of course, Einstein never actually built a laser; he was, after all, a theorist, not an engineer. Building a laser would have to wait until 1960, when Theodore Maiman and co-researchers actually built the first working laser. But prior to the first laser, a slightly different version of the same concept had been designed. In 1954 Charles Townes (Columbia University) and James Gordon (Bell Labs) in the U.S. and Nikolai Basov and Alexander Prokhorov of the Lebedev Institute of Physics, Moscow, developed the first maser, microwave amplification by stimulated emission of radiation. This instrument showed the feasibility of building a laser and it set many scientists; e.g., Arthur Schawlow and Charles Townes, to speculate about using visible light to achieve the same goal. Their research led them to construct an optical cavity that contained two highly reflecting mirrors with the amplifying medium between them. On the basis of this work they thereafter applied for the first patent for an “optical maser”.
Gordon Gould, a graduate student working with Townes worked to build a visible light instrument similar to the optical maser, but he called it a laser. He was the first person to coin the term. He began work on his laser in 1958, but he failed to file a patent until 1959. His patent was denied in favor of Townes’ and Schawlow’s patent. In 1987, Gould was finally granted patent rights for a gas-discharge laser, following a protracted 30-year legal battle.
Theodore Maiman of the Hughes Research Laboratories actually built the first laser, using a synthetic ruby crystal as the lasing medium. The ruby was silvered on both ends, one end completely and the other one partially. It was stimulated using flashes of intense light from a xenon flashtube. The first demonstration of laser light occurred on May 16, 1960. This laser is referred to as a pulsed laser, meaning that the laser light emanated in a series of pulses.
The first continuous laser using helium and neon gases was developed at Bell Labs by Ali Javan, William Bennett and Donald Herriot. It was demonstrated on December 12, 1960, just months after Maiman’s laser debuted. The He-Ne laser was the first to be stimulated by an electric current rather than a light pulse. He-Ne lasers were the first lasers to be mass-produced and they found widespread commercial use, from store UPC barcode scanners to video disc players and medical technologies and laser printers. Today they have largely been replaced by diode-pumped solid state lasers and laser diodes.
In 1961, the first neodymium glass (Nd-glass) laser was demonstrated. This type of laser, much refined, is what is used in the National Ignition Facility’s 102-laser device (see “More on national security”, below).
Nineteen sixty-two saw many advancements on the laser front. In that year the first gallium-arsenide (Ga-As) laser was developed. This was a semi-conductor device that converted electrical energy into IR light; it needed to be cooled to operate. Also developed in 1962 was the gallium arsenide phosphide (GaAsP) “visible red” laser diode. It was the precursor to today’s red LED used in CD and DVD players. The first yttrium aluminum garnet (YAG) laser was also developed in 1962.
Carbon dioxide lasers were developed in the early 1960s (Kumar Patel at Bell Labs in 1964 made the first). It is still one of the most useful of all types, due in no small part to the persistent efforts by Patel to find new uses for his device.
In industry, the CO2 laser is used for welding, drilling and cutting, even at the microscopic level. In medicine it is used in laser surgery, as well as noninvasive procedures. In science, it is used to analyze the composition of the upper atmosphere, even detecting pollutants down to parts per trillion (ppt). In military applications, the CO2 laser was used in Ronald Reagan’s “Star Wars” laser defense system.
Nineteen sixty-six saw a breakthrough involving fiber optics. It was discovered that pure glass fibers could be used to transmit light over 100 km. Telecommunications via fiber optics was born. ()
In 1970 another new type of laser was developed, called an excimer laser—short for excited dimer laser. The first excimer laser (1970) produced a xenon dimer (Xe2), excited by an electron beam. It underwent stimulated emission at the 172 nm wavelength. These excimers can only exist in an energized state, and they generally produce laser light in the ultraviolet range of the electromagnetic spectrum.
Within five years an improved version, an exciplex, had been developed. These lasers used a noble gas—argon, krypton or xenon—and a reactive halogen gas (fluorine or chlorine) as the laser medium. At high pressure and electric stimulation, the two gases form a pseudo-molecule, an exciplex, an excited complex. Like excimers, exciplexes only exist in the excited state and they also produce light in the UV range. Today, most excimer lasers are really exciplex lasers, since they use two different gases, while a dimer is a diatomic molecule of only one gas. The term exciplex, however, has not caught on.
Over the years, laser discoveries have been mixed with new uses for those developed lasers. The new laser discoveries typically became more complex, but they also became more “user-friendly” as lasers were miniaturized and became part of everyday life. Uses of lasers are discussed later in this Teacher’s Guide.
More on laser science and chemistry
A series of short (1–2 page) articles in past ChemMatters issues called “Question from the Classroom:” dealt with questions posed by students themselves and answered by Bob Becker. One such article appearing in the April 2003 issue was “How do lasers work and what is so special about laser light?”
Here’s Bob’s response:
The answers can be found in one very excited group of electrons!
You may recall that an atom’s electrons can only exist in very specific, discrete energy levels. When they absorb energy, they can become excited from their ground state up to a higher level. Being unstable there, however, they immediately drop back to a lower level, and when they do, they emit a photon of light.
The energy of this photon depends on the specific electron drop that occurred. For example, in a hydrogen atom, an electron dropping from level 3 to level 2 emits light with a wavelength of precisely 656 nm—a red band in the visible spectrum.
In a similar way, fluorescent lights make indirect use of gaseous mercury atoms whose electrons are excited by electrical current. Because the ground state is more stable, only a small fraction of the mercury atoms are in the excited state at any point in time. When an emitted photon strikes another mercury atom, it will most likely be in the ground state, so it will probably absorb the photon, only to reemit it immediately afterward.
The UV light emitted as the electrons fall back to their ground states is invisible—not exactly what you want in a light bulb. Then how do fluorescent bulbs light up your classroom? Visible light results when ultraviolet light emitted by the mercury strikes the phosphor coating on the inside of the bulb.
Laser devices also involve excited electrons, but there is an important difference. The sample inside the device is being constantly pumped with a steady stream of sufficiently high energy.
Under this condition, a population Inversion can occur. This means that there are more electrons in the excited state than there are in the ground state at any point in time. In this high-energy environment, a remarkable chain of events can occur:
[pic]
Should this pair of photons happen to approach yet another excited atom, a third photon will join their ranks, and so on. These synchronized photons are known as coherent light, for they do not tend to spread apart the way regular light does as it travels along.
Thus, the laser device simply consists of some medium to be excited (which can vary from a gas mixture to a dye molecule to a ruby crystal) and an “energy pump” pumping fast enough to cause a population inversion in that medium.
But there is one more important feature: a pair of mirrors facing one another on either end of the excited medium. It is important to remember that when the sample of atoms is excited and starts emitting light, the photons are emitted randomly in all different directions. In the laser device, most of these photons are lost as they get absorbed into the sidewalls. A small fraction, however, will just happen to emit their photons precisely perpendicular to one of the two mirrors. This beam of photons will effectively have an infinite path through the medium. Try positioning yourself between two perfectly parallel mirrors, and you’ll witness this infinite pathway.
And as the photons bounce back and forth between the two mirrors, they stimulate more and more excited electrons to drop and recruit more and more coherent photons, amplifying the beam with each passage.
This light amplification by the stimulated emission of radiation goes by the familiar acronym “LASER”. But this laser beam would be trapped inside the tube, bouncing back and forth forever, if it were not for the fact that one of the two mirrors is only partially reflective, allowing some of the coherent light to escape as a narrow beam. Because this beam does not tend to spread apart, its energy can be focused in ways that regular light cannot. This makes lasers much more powerful—and dangerous—than ordinary light.
From guided missiles to supermarket bar-code scanners, from CD players to fiber-optic phone connections, from tattoo removal to delicate eye surgery, there is no question that our world would be quite different if it were not for lasers. But without question, laser pointers should never be treated as toys. It’s very likely your school district has banned them for non-classroom use.
(Becker, R. Question from the Classroom. ChemMatters 2003, 21 (2), pp 2–3, )
And here is an excerpt from the Teacher’s Guide that accompanied the issue containing the Becker article, above.
The article nicely explains the nature of laser light and how it is created. A concise answer to the question about how laser light differs from ordinary light has three points:
(1) Laser light is monochromatic. It consists of only one specific wavelength, although this wavelength will be different for different types of lasers. It is possible to have regular non-laser light that is monochromatic. But we don’t often encounter this in our everyday world. One possible exception is that of certain yellow street lights. These are sodium vapor lights and are nearly monochromatic.
The specific wavelength of light emitted by a laser simply depends on the magnitude of the energy difference between the two energy levels in the atoms that emit the laser light. The greater this energy difference, the higher the frequency, the shorter the wavelength, and the more energy carried by each photon of the light.
(2) Laser light is coherent. This is one of the key differences between it and normal light. In laser light all the waves are moving in unison. In regular light the waves move independently. Laser light is more organized. You might think of a highly trained army marching along “in step,” vs. a bunch of people just casually walking across a field.
(3) Laser light is directional. The beam is very tight and concentrated. All the light moves in the same direction, as opposed, for example, to the light emitted from a flashlight or an incandescent bulb, which moves off in all different directions.
(Teacher’s Guide to Becker, R. Question from the Classroom. ChemMatters 2003, 21 (2), pp 2–3)
The helium-neon (He-Ne) laser is the one most frequently used in high school physics labs because it is relatively inexpensive and relatively safe. It is classified as a neutral gas laser. The energy transitions for this laser are fairly easy to understand. The gas mixture (~5–10:1, He:Ne) inside the laser cavity is first zapped (pumped, in laser terms) with approximately 1000 volts of electricity.
The laser process in a HeNe laser starts with collision of electrons from the electrical discharge with the helium atoms in the gas. This excites helium from the ground state to the 23S1 and 21S0 long-lived, metastable excited states. [See diagram.] Collision of the excited helium atoms with the ground-state neon atoms results in transfer of energy to the neon atoms, exciting them into the 2s and 3s states. This is due to a coincidence of energy levels between the helium and neon atoms.
This process is given by the reaction equation:
He* + Ne → He + Ne* + ΔE
where (*) represents an excited state, and ΔE is the small energy difference between the energy states of the two atoms, of the order of 0.05 eV.
The number of neon atoms entering the excited states builds up as further collisions between helium and neon atoms occur, causing a population inversion between the neon 3s and 2s, and 3p and 2p states. Spontaneous emission between the 3s and 2p states results in emission of 632.8 nm wavelength light, the typical operating wavelength of a HeNe laser.
After this, fast radiative decay occurs from the 2p to the 1s energy levels, which then decay to the ground state via collisions of the neon atoms with the container walls. Because of this last required step, the bore size of the laser cannot be made very large and the HeNe laser is limited in size and power.
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And we would be remiss if we did not mention safe use and potential hazards involved in the use of lasers. Here is another excerpt from the April 2003 ChemMatters Teacher’s Guide, this one dealing with the biological classifications of lasers.
There are four broad categories of lasers with a couple of sub-categories that relate to their potential for causing biological damage. All lasers should be labeled as to their biological classifications.
Class I—These are the least harmful. They cannot emit radiation at any known harmful level. They are typically found in devices like laser printers, CD players, CD ROM devices and laboratory analytical equipment. There are no safety requirements governing their use.
Class IA—This classification applies only to lasers that are “not intended for viewing.” The upper limit to the power output of these kinds of lasers is set at 4.0 mW, or 4.0 mill joules per second.
Class II—These are considered to be low-power lasers, but more powerful than Class I. Their upper limit is 1 mW. Although a laser of this power can cause eye damage, it is assumed that this is not likely to occur because of the human tendency to quickly blink or in some other way divert their eyes when they are exposed to a bright light. Some laser safety Web sites state that you would have to look at one of these lasers for an extended period of time, perhaps as long as 15 minutes in order to sustain eye damage. Some laser pointers fall into this category.
Class IIIA—These are considered to be of intermediate power, between 1-5 mW. Most pen-like pointing lasers fall into this category. These are considered to be more hazardous than Class II lasers and are never to be viewed directly. A Class IIIA laser should never be pointed at a person’s eyes nor should the light ever be viewed with a telescopic device.
Class IIIB—These are considered to be of intermediate power, between 5-500 mW. These are often used in spectrometry devices and entertainment light shows. These are considered to be quite hazardous. They should never be viewed directly. Even diffuse reflections can be dangerous.
Class IV—These are very high-powered lasers, up to 500 mW. They are used in surgery, research, drilling, cutting and welding. These are very dangerous, not only to the eyes, but to the skin as well. They can also constitute a fire hazard.
(Teacher’s Guide to Becker, R. Question from the Classroom. ChemMatters 2003, 21 (2), pp 2–3)
More on uses of lasers
Excimer lasers
The wavelength of an excimer laser depends on the molecules used as the lasing medium, and is usually in the ultraviolet region of the electromagnetic spectrum:
|Excimer |Wavelength |Relative Power |
| | |mW |
|Ar2* |126 nm | |
|Kr2* |146 nm | |
|Xe2* |172 & 175 nm | |
|ArF |193 nm |60 |
|KrF |248 nm |100 |
|XeBr |282 nm | |
|XeCl |308 nm |50 |
|XeF |351 nm |45 |
|KrCl |222 nm |25 |
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These shorter wavelength lasers produce energy that is absorbed by biological material as well as organic compounds. The effect is not burning or cutting, but rather a disruption of chemical bonds at the surface material. This effectively disintegrates into the air in a process known as photoablation. This results in removal of very thin layers of the surface material with almost no heat and no subsequent damage to underlying material. These characteristics make excimer lasers very useful in delicate surface surgery, as in dermatology and especially in eye surgery. It is also useful for precisely “micro-machining” organic materials, including some polymers and plastics.
Eye surgery
LASIK® surgery and some other types of eye surgery use laser technology. (LASIK is an acronym for Laser-Assisted in Situ Keratomileusis). The lasers used for LASIK are excimer lasers, which generate laser light at 193 nm. An incision is made across the corneal surface to create a flap, which can then be folded back to allow access to the tissue inside the cornea. The instrument used to create this flap is a microkeratome, a metal scalpel of sorts. The excimer laser is then used to cut away some of the underlying corneal tissue to resculpt the cornea to improve vision.
Today, more advanced LASIK facilities use two different lasers for “bladeless” eye surgery. A new device, the femtosecond laser, is used to cut the corneal flap, exposing the rest of the cornea for surgery by the excimer laser. The femtosecond laser produces bursts of laser light at 1053 nm (in the infrared region of the electromagnetic spectrum), a much longer wavelength and therefore lower energy light than the excimer laser. The cornea is transparent to the femtosecond pulses and is not damaged by them. The shorter wavelength excimer laser light will destroy corneal tissue, but only very tiny amounts at a time, in order to reshape the cornea. The process of removing corneal tissue is known as photoablation. It is not really a burning of tissue, but rather a vaporizing of the tissue as it breaks carbon-carbon bonds.
The femtosecond laser is a vast improvement over the metal blade, as it results in much more accurate cuts and far fewer post-operative complications. ()
The femtosecond laser procedure was developed at the University of Michigan in 2003. ()
Skin surgery
Excimer lasers are also used for other types of surgeries, including dermatological applications and even angioplasty. The only major disadvantage to excimer lasers is their rather large size, which makes them less desirable for their medical applications. Future development may decrease their size.
Photolithography—making computer chips
Other uses include photolithography, manufacturing microelectronic devices like semiconductor integrated circuits. A newer version of excimer laser involves the use of KrF and ArF dimer lasers that produce even smaller wavelength UV light called deep UV. Use of deep UV lithography has miniaturized electronic chip manufacture to the 22-nm level, allowing the continuance of Moore’s law for at least another decade. (Moore’s law states that the number of transistors on integrated circuits doubles approximately every two years.)
Newer developments in excimer laser use
Excimer lasers are being used in these developmental areas as well:
• Silicon annealing and recrystallization—used in flat-screen technology
• Micromachining of plastic parts—used in inkjet nozzle drilling in inkjet printers
• Surface modification—used in greener automobile manufacturing; e.g., Audi cars
• Pulsed Laser Deposition (PLD)—used in making superconducting tape
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The excimer laser has become an indispensible tool of our technological world, so much so that President Barack Obama awarded Samuel Blum, Rangaswamy Srinivasan and James Wynne, all from IBM, and co-inventors of the ultraviolet excimer laser, a National Medal of Technology and Innovation. Gholam Peyman, the retina surgeon credited with invention of the Lasik eye surgery procedure (which uses the excimer laser), from Arizona Retinal Specialists, was also awarded one of these prestigious medals.
More on national security
The U.S. National Ignition Facility (NIF), headquartered at the Lawrence Livermore National Laboratory, is charged with three missions:
• National Security: How do we ensure the nation’s security without nuclear weapons testing?
• Energy for the Future: Where will the world’s energy come from when all the fossil fuels are gone? and How can we produce the energy we need without causing catastrophic climate change?
• Understanding the Universe: How did the universe come into being? How did the stars and planets form? What happens in supernovas and black holes?
One of the facility’s primary goals has been to develop conditions which could initiate a fusion reaction. To reach this goal, the program has built a huge building (think ten stories high, the size of three football fields) to contain an experiment that uses192 very powerful lasers all aimed at a tiny target in the target chamber in the center of the building. The incident ultraviolet light energy will be approximately 2 million joules of energy, all impacting the central target simultaneously. This energy will create “conditions similar to those that exist only in the cores of stars and giant planets and inside a nuclear weapon. The resulting fusion reaction will release many times more energy than the laser energy required to initiate the reaction.” ()
In order to ensure that the output of the 192 beamlines is uniform, the initial light is generated from a single source—a low-power flash of 1053 nm infrared light. This is generated by an ytterbium-doped solid state optical fiber laser. The flash from this driver laser is then split and sent into 48 preamplifier modules which amplify the beams. The partially-amplified light goes into the system of 192 flashlamp-pumped neodymium-doped phosphate glass lasers to be greatly amplified before entering the target chamber. A much more detailed account of the generation process can found at , or at the NIF Web site:
The light emitted from these 192 lasers is infrared light, which is later converted to ultraviolet light just before impacting the target. The 2 million Joules of laser energy slamming into “millimeter-sized targets ... can generate unprecedented temperatures and pressures in the target materials—temperatures of more than 100 million degrees and pressures more than 100 billion times Earth’s atmosphere.” () Initiating the fusion reaction will simultaneously further the goals of the three missions discussed above. As of the writing of this Teacher’s Guide, experiments called “shots” have already produced 1.89 MJ of energy inside the NIF—very close to the 2 million MJ expected to be required for fusion initiation.
But fusion initiation is not the only experiment being done in NIF. Other laser shots will help scientists better understand properties of material under extreme conditions and hydrodynamics, “the behavior of fluids of unequal density as they mix”. Extremely high-speed cameras (a billion frames a second!) inside the target chamber can be used to diagnose the results of the experiments.
This video clip describes how the NIF laser-induced fusion reaction will work: . If this is unavailable, you can also access it on YouTube at .
Selected other uses for lasers
Consumer
• Laser pointers
• Gunsights and targeting systems
• CD and DVD players
• Leveling devices
• Fiber optics for data and telecommunications
• Supermarket barcode scanners
• Laser printers
• Holograms
Research
• Spectroscopy
– UV-Vis
– IR
– Fluorescence
– Raman
– Non-linear
– Laser-induced Breakdown (of molecules)
• Laser-induced chemical reactions
• Monitoring of chemical intermediates in reactions
• Detection of pollutants in air, in wastewater
• Creating extremely low temperatures at the atomic level
Industry
• Transfer energy to different materials very quickly (cooling and heating)
• Welding
• Cutting
• Drilling
• Marking
• Scribing
• Soldering
• Micro-machining
• Heat treating
• Metal deposition
• Paint stripping and surface removal
• Measuring
– Distances–remote sensing
– Concentrations
– Cylindricity of ball bearings
– Thickness by shadow
– Speed (LIDAR, like radar, only with laser)
Medicine
• Precision surgery
• Tumor removal/ablation
• Cosmetic surgery
• Dermatology
• Dentistry
• Laser acupuncture
More on osteoid osteoma
This excerpt from a Web-published medical report from the Royal Belgian Society of Radiology affirms claims made about osteoid osteoma in the ChemMatters article. The report concerns a 32-year old man complaining of recurrent pain in the upper thigh.
Radiological diagnosis
Clinical data and imaging findings are strongly suggestive for a subperiosteal osteoid osteoma of the right acetabulum. Patient underwent a percutaneous CT guided thermocoagulation [needle through the skin and laser heating, tissue destruction of the lesion and had no more pain after this procedure. Biopsy confirmed the diagnosis.
[Editor’s note: This means the CT scan tells where the tumor is; the needle is inserted there through the skin (percutaneous); the laser does the thermo-ablation and heats the tumor to oblivion; the patient is all better, just like the ChemMatters article said.]
Discussion
Osteoid osteoma is a well known benign osteoblastic tumor, most commonly found in the cortical bone of the long bone shaft and spine. Fusiform sclerosis and a central nidus [place of origin] are seen on radiographs, CT and MRI. The nidus is “hot” on scintigraphy.
Subperiosteal extra-osseous lesions are rare and arise adjacent to bone, usually in the femoral neck, talar neck, hand and foot. Patients are young, usually between 5-40 years. Male/female ratio is 2-3:1. Pain is almost invariably the presenting complaint. Pain relief is accomplished with acetylsalicylic acid. Surgical excision or percutaneous CT guided thermo-ablation are curative and will bring dramatic relief of symptoms.
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More on laser treatment of tumors
The laser used in the treatment of Chris’ osteoid osteoma may well have been a neodymium-doped yttrium-arsenic-garnet (Nd:YAG) laser. “Nd:YAG lasers emitting light at 1064 nm have been the most widely used laser for laser-induced thermotherapy, in which benign or malignant lesions in various organs are ablated by the beam.”
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The National Cancer Institute Web page on laser treatment of cancer provides this information:
Key Points
• Laser light can be used to remove cancer or precancerous growths or to relieve symptoms of cancer. It is used most often to treat cancers on the surface of the body or the lining of internal organs.
• Laser therapy is often given through a thin tube called an endoscope, which can be inserted in openings in the body to treat cancer or precancerous growths inside the trachea (windpipe), esophagus, stomach, or colon.
• Laser therapy causes less bleeding and damage to normal tissue than standard surgical tools do, and there is a lower risk of infection.
• However, the effects of laser surgery may not be permanent, so the surgery may have to be repeated.
1. What is laser light? [We already know the answer to this one.]
The term “laser” stands for light amplification by stimulated emission of radiation. Ordinary light, such as that from a light bulb, has many wavelengths and spreads in all directions. Laser light, on the other hand, has a specific wavelength. It is focused in a narrow beam and creates a very high-intensity light. This powerful beam of light may be used to cut through steel or to shape diamonds. Because lasers can focus very accurately on tiny areas, they can also be used for very precise surgical work or for cutting through tissue (in place of a scalpel).
2. What is laser therapy, and how is it used in cancer treatment?
Laser therapy uses high-intensity light to treat cancer and other illnesses. Lasers can be used to shrink or destroy tumors or precancerous growths. Lasers are most commonly used to treat superficial cancers (cancers on the surface of the body or the lining of internal organs) such as basal cell skin cancer and the very early stages of some cancers, such as cervical, penile, vaginal, vulvar, and non-small cell lung cancer.
Lasers also may be used to relieve certain symptoms of cancer, such as bleeding or obstruction. For example, lasers can be used to shrink or destroy a tumor that is blocking a patient’s trachea (windpipe) or esophagus. Lasers also can be used to remove colon polyps or tumors that are blocking the colon or stomach.
Laser therapy can be used alone, but most often it is combined with other treatments, such as surgery, chemotherapy, or radiation therapy. In addition, lasers can seal nerve endings to reduce pain after surgery and seal lymph vessels to reduce swelling and limit the spread of tumor cells.
3. How is laser therapy given to the patient?
Laser therapy is often given through a flexible endoscope (a thin, lighted tube used to look at tissues inside the body). The endoscope is fitted with optical fibers (thin fibers that transmit light). It is inserted through an opening in the body, such as the mouth, nose, anus, or vagina. Laser light is then precisely aimed to cut or destroy a tumor.
Laser-induced interstitial thermotherapy (LITT), or interstitial laser photocoagulation, also uses lasers to treat some cancers. LITT is similar to a cancer treatment called hyperthermia, which uses heat to shrink tumors by damaging or killing cancer cells. (More information about hyperthermia is available in the NCI fact sheet Hyperthermia in Cancer Treatment.) During LITT, an optical fiber is inserted into a tumor. Laser light at the tip of the fiber raises the temperature of the tumor cells and damages or destroys them. LITT is sometimes used to shrink tumors in the liver.
Photodynamic therapy (PDT) is another type of cancer treatment that uses lasers. In PDT, a certain drug, called a photosensitizer or photosensitizing agent, is injected into a patient and absorbed by cells all over the patient’s body. After a couple of days, the agent is found mostly in cancer cells. Laser light is then used to activate the agent and destroy cancer cells. Because the photosensitizer makes the skin and eyes sensitive to light afterwards, patients are advised to avoid direct sunlight and bright indoor light during that time. (More information about PDT is available in the NCI fact sheet Photodynamic Therapy for Cancer.)
4. What types of lasers are used in cancer treatment?
Three types of lasers are used to treat cancer: carbon dioxide (CO2) lasers, argon lasers, and neodymium:yttrium-aluminum-garnet (Nd:YAG) lasers. Each of these can shrink or destroy tumors and can be used with endoscopes.
CO2 and argon lasers can cut the skin’s surface without going into deeper layers. Thus, they can be used to remove superficial cancers, such as skin cancer. In contrast, the Nd:YAG laser is more commonly applied through an endoscope to treat internal organs, such as the uterus, esophagus, and colon.
Nd:YAG laser light can also travel through optical fibers into specific areas of the body during LITT. Argon lasers are often used to activate the drugs used in PDT.
5. What are the advantages of laser therapy?
Lasers are more precise than standard surgical tools (scalpels), so they do less damage to normal tissues. As a result, patients usually have less pain, bleeding, swelling, and scarring. With laser therapy, operations are usually shorter. In fact, laser therapy can often be done on an outpatient basis. It takes less time for patients to heal after laser surgery, and they are less likely to get infections. Patients should consult with their health care provider about whether laser therapy is appropriate for them.
6. What are the disadvantages of laser therapy?
Laser therapy also has several limitations. Surgeons must have specialized training before they can do laser therapy, and strict safety precautions must be followed. Laser therapy is expensive and requires bulky equipment. In addition, the effects of laser therapy may not last long, so doctors may have to repeat the treatment for a patient to get the full benefit.
7. What does the future hold for laser therapy?
In clinical trials (research studies), doctors are using lasers to treat cancers of the brain and prostate, among others. To learn more about clinical trials, call NCI’s Cancer Information Service at 1–800–4–CANCER or visit the clinical trials page of NCI’s Web site.
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Laser treatment of tumors is not the only game in town, either; treatment of tumors by thermal ablation can be done using many different moieties. “Thermal tumor ablation modalities either freeze or heat tumors to lethal temperatures. These include cryoablation, radiofrequency (RF), microwave, laser and high-intensity focused ultrasound (HIFU).”
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Especially for liver tumors, invasive surgery is often not the answer, as liver cancer is often discovered in late stages of development, potentially with many tumors spread throughout the liver. Image-guided tumor ablation then becomes the best choice for treatment for these types of cancers.
More on the effect of heat on tumors
Local hyperthermia (ablation) is the process of heating tumors to the point of extinction. The effect of increased temperature on tumor cells is to desiccate the cells, thereby destroying them and the tumor, coagulating nearby proteins and destroying blood vessels that had supplied blood to the tumor. In effect, the cells are “cooked”. The hoped-for outcome is total destruction of the tumor, or at least diminishing its size and slowing its growth. As mentioned previously, thermal ablation can use any of the following sources of energy. Here is a short video clip from the University of Wisconsin-Madison that describes thermal ablation:
• Radio frequency ablation (RFA)
• Ultrasound ablation (HIFU—high intensity focused ultrasound)
• Laser ablation
• Microwave ablation
• Electric current
The method the doctor finally chooses to use depends on many factors; e.g., size of the tumor, its location, the number of tumors, proximity to other body parts, degree of comfort/familiarity of doctor with using method, cost, past efficacy, etc.
Here is a short (7:16) video clip from the University of Wisconsin-Madison that describes thermal ablation and discusses one patient’s treatment, from observations and diagnosis right through to the actual operation and follow-up: . (The video uses very detailed medical terminology, but students may actually like the video because of this.)
More on other modes of treatment
The use of lasers in the treatment of cancer is a relatively new development. Here are a few other modalities—other than surgery, radiation and chemotherapy—that have been in use for some time, and a few new ones that are getting attention as well.
From the ChemMatters Teacher’s Guide for October 2007, one article of which dealt with the life and research of Percy Julian, a specialist in developing useful products from the soy bean and the yam, comes the following:
Anticancer Drugs—There are a number of drugs used to treat cancer which are derived from plants. Among them are:
• Rosy periwinkle (Catharanthus roseus)—used to treat leukemia and Hodgkin’s Disease
• Mayapple—This plant contains podophyllotoxin, which is the starting material for producing the antitumor agent etoposide, used for the treatment of lung and testicular cancer.
• Pacific Yew(taxus brevifolia)—contains the compound taxol, used in the treatment of ovarian and breast cancer.
And the following excerpt is from the ChemMatters Teacher’s Guide for December 2001. The article for which the material was researched is “Trolling the Seas for New Medicines”:
One of the most exciting and promising of new anti-cancer drugs may be a compound called ecteinascidin (pronounced ed-TIN-aside-in) and a simpler, easier to make form called phthalascidin (pronounced THAL-aside-in). This has been described as “the most complicated molecule ever to be made on a commercial scale” by Elias, J. Corey, who won the 1990 Nobel Prize in chemistry. The two primary researchers are Corey, and one of his graduate students, Eduardo Martinez. The drug is approximately 100-500 times stronger than Taxol in inhibiting tumor cell growth, and in general is estimated to be hundreds to thousands of times more potent than most current cancer drugs. Researchers estimate that eleven pounds of the drug would be sufficient to satisfy the needs of the entire world for a year. So promising is this drug that it is being rushed through clinical trials and it is hoped that it may be available some time in 2002.
At the present time, ecteinascidin is being tested on terminally ill patients afflicted with cancers of the blood vessels, tendons, muscles, and other soft tissues. According to Corey, “There hasn’t been effective chemotherapy for such cancers.”
The drug was first discovered by Ken Rinehart of the University of Illinois in the 1980s. Rinehart obtained the original samples of the drug from sea squirts (Ecteinascidia turbinate) he collected from reefs in the West Indies.
The drug provides an excellent illustration of the difficulties often encountered in trying to isolate a drug from a marine organism. Ten pounds of sea squirts only yielded a few millionths of an ounce of ecteinascidin. Attempts to “farm” sea squirts achieved very limited success. Clearly what was needed was a way to synthesize the drug rather than obtaining it from sea squirts. Following a two-year effort, David Gin, a post-doctoral student at Harvard University, achieved the synthesis in 1996. Even then, the synthesis was tedious. A more efficient process was developed by Eduardo Martinez.
Ecteinascidin evidently works by interacting with DNA and an unknown protein contained in cancer cells. Unlike standard chemotherapy treatments, which kill cancer cells—and healthy cells as well—the drug doesn’t actually kill cells. Instead, it prevents treated cells from reproducing and growing.
When tested on drug-resistant colon, lung, melanoma, and prostate tumor cells grown in Petri dishes, the drug inhibited cell growth in all cases. If it works as well on patients, this will prove to be one of the most important anti-cancer drugs ever developed.
(Teacher’s Guide for Black, H. Trolling the Seas for New Medicines. ChemMatters 2001, 19 (4), pp 6–7).
But the oceans aren’t the only source of cancer-fighting substances. One Web page on the PBS site is called “Venom’s Healing Bite” by Kate Becker. This page focuses on six venomous animals, the fluids from whose bites or stings are being researched as potential cures for various diseases/symptoms. Three of the six studies focus on cancer treatment.
Targeting cancer
The sting of the "death stalker" scorpion, Leiurus quinuestriatus, contains neurotoxins that can paralyze and kill. But one component of this scorpion's venom, chlorotoxin, could one day save lives, too, because it is drawn to cancer cells like a magnet to iron. By combining a synthetic chlorotoxin with a radioactive form of iodine, researchers can deliver radiation directly to cancer cells. Nanoparticle-spiked chlorotoxin may also slow the spread of cancer and could help deliver gene therapy to cancer cells. Because chlorotoxin can cross the blood-brain barrier, scientists are particularly interested in using it to treat brain cancers like glioma. Chlorotoxin can also help doctors spot cancer cells by selectively "painting" them with a fluorescent beacon.
Keeping tumors in check
The bite of the southern copperhead Agkistrodon contortrix, a pit viper common in the eastern United States, is rarely fatal to humans, but it delivers a painful dose of venom. One component of the venom, a protein named contortrostatin, could stop the spread of cancer cells. Contortrostatin doesn't kill cancer cells; instead it holds them in check by interfering with surface proteins and blocking other mechanisms the cells need to move around the body. Contortrostatin also starves out tumors by staunching the growth of blood vessels that deliver nutrients to the malignant cells. Contortrostatin has been tested on breast, ovarian, prostate, melanoma, and brain cancers in mice, and researchers hope to start human clinical trials soon.
Killing cancer cells
The sharp pain of a honeybee sting is caused in part by a peptide called melittin, which kills cells by piercing holes in their membranes. To turn this indiscriminate killer into a fine-tuned cancer drug, researchers have combined it with nanoparticles and cancer-targeting agents that allow the melittin to "sting" cancer cells without harming healthy cells. Though the treatment has not yet been tested on human patients, it has shown promise on mice. Researchers also hope to harness melittin's cell-killing power to knock out other diseases, including bacterial and fungal infections and arthritis.
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From the October 14, 2010 edition of Science Daily comes this report of doctors at Mayo Clinic’s Florida campus successfully using laser ablation for kidney and liver tumors. Laser ablation has been used extensively for brain tumors, but until now (2010) it had not been used in the U.S. for soft tissue.
Physicians at Mayo Clinic's Florida campus are among the first in the nation to use a technique known as MRI-guided laser ablation to heat up and destroy kidney and liver tumors. So far, five patients have been successfully treated -- meaning no visible tumors remained after the procedure.
They join their colleagues at Mayo Clinic's site in Rochester, Minn., who were the first to use laser ablation on patients with recurrent prostate tumors.
Although the treatment techniques are in the development stage, the physicians say the treatment is potentially beneficial against most tumors in the body -- either primary or metastatic …
"Laser ablation offers us a way to precisely target and kill tumors without harming the rest of an organ. We believe there are a lot of potential uses of this technique -- which is quite exciting," says Eric Walser, M.D., an interventional radiologist who has pioneered the technique at Mayo Clinic, Florida.
In the United States, laser ablation is primarily used to treat brain, spine and prostate tumors, but is cleared by the U.S. Food and Drug Administration (FDA) for any soft tissue tumor. Only a few centers have adapted the technique to tumors outside of the brain ...
The outpatient procedure is performed inside an MRI machine [similarly for CT scan machine], which can precisely monitor temperature inside tumors. A special nonmetal needle is inserted directly into a tumor, and the laser is turned on to deliver light energy. Physicians can watch the temperature gradient as it rises, and they can see exactly in the organ where the heat is. When the tumor and a bit of tissue that surrounds it (which may harbor cancer cells) is heated to the point of destruction -- which can be clearly seen on monitors -- the laser is turned off. In larger tumors, several needles are inserted simultaneously.
Patients are given anesthesia because, during the 2.5-minute procedure they should not move, Dr. Walser says.
Dr. Walser adds that laser ablation is a much more precise technology than similar methods that use probes, such as radiofrequency ablation, which also raises a tumor's temperature, and cryotherapy, which freezes tumors.
David Woodrum, M.D., Ph.D., from Mayo Clinic, Rochester, has also reported success using the new technique.
At the March meeting of the Society of Interventional Radiology, Dr. Woodrum, presented results from the first known cases of using MRI-guided laser ablation to treat prostate tumors. He said then that the safe completion of four clinical cases using the technique to treat prostate cancer in patients who had failed surgery "demonstrates this technology's potential."
Dr. Woodrum has now treated seven patients, including a patient with melanoma whose cancer had spread to his liver.
"MRI-guided ablation may prove to be a promising new treatment for prostate cancer recurrences," he says. "It tailors treatment modality (imaging) and duration to lesion size and location and provides a less invasive and minimally traumatic alternative for men."
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Connections to Chemistry Concepts
(for correlation to course curriculum)
1. Electromagnetic spectrum—Wavelengths and frequency for laser light can be calculated, just as for “normal” light.
2. Properties of light—Light behaves both as a particle and as a wave, and both can be used to discuss how a laser works and what its output is. Frequencies, wavelengths and energies of photons are all related to the speed of light via Einstein’s equation, E = mC2. These properties of laser light are identical to those of “normal” light. The only difference is that the green (for example) laser light is much more intense and has much more energy associated with it only because there are so many photons in the beam of laser light. The energy per photon of green light is the same for laser light and normal light.
3. Atomic theory—From Bohr’s model of the atom and spectral lines to the quantum theory, and the wave/particle duality of light, lasers fit right in.
4. Electrons and energy levels—excited and ground states—All the reactions discussed with the lead-acid and lithium-ion batteries involve oxidation and reduction reactions.
5. Periodic Table—Elements on the periodic table are arranged according to physical and chemical properties. Students may be able to see a correlation between some of the elements that are useful in lasers with their positioning on the table.
6. Chemical and physical properties—These properties make specific elements or compounds useful for specific types of lasers.
Possible Student Misconceptions
(to aid teacher in addressing misconceptions)
1. “Laser pointers are harmless; everybody has them.” Although “everybody” may have them, that doesn’t make them harmless. They are relatively safe as long as one makes sure NOT to point them directly at someone else’s (or their own) eyes. And if you watch the news, you may occasionally see that someone has been arrested for shining a green laser at a low-flying airplane or helicopter. These lasers are powerful enough to do retinal damage if they are shined into one’s eyes—even at fairly long distances. A pilot can be blinded by the light if it shines directly into his eyes, and this could cause him to crash the airplane.
2. “Lasers are just very bright lights.” While it’s true that they’re bright lights, there’s more to them than just that. They are also monochromatic (having only one wavelength), and the photons of light emitted are all in phase (“traveling in the same direction”, according to the article), and the photons are very focused into a narrow beam. This makes laser light much more intense—and dangerous—than “normal” light.
3. “If lasers can surgically remove tumors, then they can be used to cut out all types of cancers within the body.” Whoa, not so fast! Laser light can be used effectively to surgically remove lumps of cancerous tissue—tumors—which are concentrated in one part of the body. Using laser light to cut out many small tumors throughout the body (when the cancer has metastasized, for instance) would be almost impossible, as doctors would be unable to insert a needle into each one of these small cancerous blobs to destroy them. And the more cancerous cells there are, the more likely that some of the laser light might miss its intended target and hit (and destroy) healthy tissue.
4. “Everybody should have a CT scan to make sure they don’t have any tumors.” CT scans are actually X-rays that pass through the body. The CT scan uses more radiation than a normal X-ray, and exposes the body to radiation that could damage DNA in cells that could actually produce cancerous cells, rather than just detect them. Doctors must determine if the benefits of detecting tumors with the CT scan outweigh the risks of causing cancers with the CT scan. Costs of CT scans must also be taken into consideration when doctors weigh benefits and risks. And some tumors that are discovered may be benign and cause no problems for the patient, but he/she might still demand that the tumors be removed at great cost to society, for little real benefit.
5. “It should be easy for a doctor to cut that thin layer of skin with a laser. After all, the laser beam makes a bright, straight line right to the target so it’s easy to see the beam, just like in all the ‘Star Wars’ movies.” Actually, those laser beams shining through the vacuum of space so you can see where they’re going is really just science fiction, not science fact. You can’t generally see a laser beam until it hits its target, whatever that might be. Remember that the beam is photons all traveling in the same direction, so they can’t be seen from the sides of the photon path, unless there’s dust in the air that might deflect some of the photons. (In the case of higher energy green or blue laser light pointers, you might be able to see their beam due to Rayleigh scattering on individual molecules in the air.)
Anticipating Student Questions
(answers to questions students might ask in class)
1. “Who discovered the laser?” See “More on the history of the laser”, above.
2. “What’s the difference between sunlight and laser light?” Several differences exist between sunlight and laser light:
Sunlight Laser light
a. Broad spectrum light—made of a. Monochromatic, or almost so—made of only
many wavelengths of light one, or very few wavelengths of light
b. Incoherent—spreads out as it b. Coherent—disperses very little as it travels,
travels all photons are in phase
c. Non-directional and not focused— c. Directional and focused—nearly parallel beam
light is generated in all directions of photons (when collimated)
from source
3. “What is an excited state? A ground state? How electrons get from one to the other? And how does that make laser light?” Let’s start with the ground state. Electrons are usually in the ground state, their lowest energy state within the atom. When they are zapped with electricity or light, electrons absorb this energy and jump to higher energy states; these are the excited states. In most cases, excited states are very transient—electrons are more stable in the ground state, so they almost instantaneously jump back down (in energy terms) to the ground state and release that extra energy they absorbed when they became excited And that is “normal” light. But in some cases, the excited state is just a tad more stable than normal—a metastable state. In this state, the electrons can maintain their higher energy for a brief time. If sufficient numbers of ground-state electrons reach this metastable excited state, they can form a population inversion wherein more metastable excited electrons exist than stable ground-state electrons. At this point, it another high-energy photon or electron (probably from pumping) comes along, it will induce a metastable excited electron to jump to the ground state, thereby emitting a photon, which can induce another excited electron to do likewise, etc. All the electrons jumping to the ground state en masse generate all the photons that become the laser beam.
4. “What do they use to make a laser?” Scientists can use a lot of different things to make lasers because there are a lot of different types of lasers: gas lasers, solid state lasers, semiconductor lasers, metal-vapor lasers dye lasers, and free-electron lasers, just to name a few. A laser can contain any one, two, or more of these elements (and perhaps others):
He N2 O Ne Ar
Ti Cr Cu Se Kr
Y Cd I Xe Ce
Pr Sm Nd Ho Er
Tm Yb Au Hg U
They can also contain HF, CO, CO2, C2H4, CaF2, ArF, KrF, XeCl, XeF, various organic dyes, some minerals (chrysoberyl, garnet and sapphire, for example), and some semiconductors, such as GaN, AlxGa1-xAs and YAG (yttrium aluminum garnet).
5. What is the ‘laser medium’ the article talks about?” The “medium” is the substance that undergoes pumping, absorbing electrical or photonic energy that sends some of the medium’s electrons to higher, usually metastable energy levels to provide the population inversion required to initiate the generation of laser light. The materials above are all potential laser “mediums”.
6. “What’s the difference between the commonly available red lasers used for laser pointers and the less common green laser used for the same purpose?” Well, one’s red and one’s green … OK, sorry, here we go. The red lasers that are prevalent today, used for laser pointers, emit light in the 630–700 nm region of the spectrum, with the most common wavelengths being 635 [ruby red], 655 [red-orange] and 671 nm. The green laser emits between 490 and 560 nm, with the most common being 532 nm [emerald green]. Red lasers can simply use a red laser diode and a lens to generate the laser beam; however, no similar diode exists for the green region of the spectrum, so the green laser uses a diode that emits in the 808 nm region of the spectrum (in the infrared).A crystal then converts the 808 nm to 1064 nm and a second, polarized crystal doubles the frequency, halving the wavelength to the green 532 nm light. This makes the green laser pointer much more expensive than its simpler red counterpart.
Another difference between the two lasers is visibility. The human eye is much more sensitive to green light than to red light. This is why the green laser beam seems so much brighter than the red (from 10-50 times brighter). () The green laser pointer is most likely a DPSS (diode pumped solid state) laser or a DPSSFD (diode pumped solid state frequency-doubled) laser. An announcement was made in 2009 that a direct green laser that does not require doubling the frequency had been developed. This could open (has opened) the door for a laser-based RGB laser projector, since red and blue laser diodes already exist. () This source shows cutaway schematics of both laser pointers for comparison: .
Yet another difference between the two lasers is that the red beam is usually not visible until it hits its target, while the green beam is visible all the way to its target, due to Rayleigh scattering. This makes it useful for astronomers to point out specific stars or constellations in the night sky.
7. “What makes the green laser pointer more dangerous than the red pointer?” First, a green laser light photon has a shorter wavelength than one of red light. That means it has a higher frequency and therefore a higher energy. More energy means more potential damage to the eye (assuming that’s the danger you’re referring to), so this may be at least part of the reason it is potentially more dangerous. But there are two other factors to consider. 1) The total energy of the beam is also dependent on the number of photons; one green photon doesn’t have as much energy as, say, a hundred red photons. So if the green laser pointer actually is brighter or more intense (more dangerous), it may be because it has a higher wattage rating (say, 10 mW vs. 5 mW for a red pointer) that delivers more photons per second than does the red laser light. 2) The sensitivity of the eye to each wavelength/color of light. We’ve already said above that the human eye is more sensitive to green light than to red. That means that green light of equal intensity to red would appear to us to be brighter (maybe more destructive to eye tissue), even though that may not be the case.
8. “Why is general anesthesia needed for this laser surgery?” The patient is given a general anesthesia because the laser must be focused exactly on the tumor and that requires that the patient remain completely still so the laser doesn’t go roaming about killing innocent nearby tissue. Being unconscious leaves you pretty still, eh? Also, I imagine the placement of the needle—through the skin—doesn’t tickle, either.
9. “How do radio waves and lasers differ in cancer treatment?” Radio frequency ablation is effective, but in addition to heating up the tumor tissue, it also raises the temperature of nearby tissue (it is less focused); laser ablation only heats up the tissue at which it is aimed—the tumor (laser light is more focused, remember?). Laser ablation is also much quicker—perhaps as much as five or more times faster—than radio frequency ablation. This results in fewer complications and quicker surgery.
10. “What other uses are there for lasers?” Lasers are used widely in many different applications across a variety of industries. See “More on uses of lasers” above for more information.
In-class Activities
(lesson ideas, including labs & demonstrations)
1. The National Ignition Facility at the Lawrence Livermore National Laboratory in California offers a video or audio clip (you choose) dealing with their “Super Laser at the NIF”. It comes complete with California Science Standards, a glossary of science terms, background information for the student, a “Segment Summary Student Sheet” and a “Personal Response Student Sheet”. It also includes specific questions the teacher can ask students to answer through their viewing of the video. Download the pdf file at . The video and/or audio clips are also available at this same site.
2. An experiment from Middlebury College to build a He-Ne laser from “readily available optical components is described here: . Although the lab itself may be more than you want to or can do, it does contain an energy level diagram of the energy levels and jumps of electrons from helium and neon responsible for the laser effect.
3. You can definitely connect the energy transitions of some laser action; e.g., the He-Ne laser, to electron energy positions and transitions within atoms. (See 2, above.)
4. Experiments with lasers:
a. There are two experiments students can do using lasers to a) measure the wavelength of laser light and b) determine the amount of data on a CD. Both are discussed in this lab procedure from Harvard: . Note that these are really physics labs, rather than chemistry labs.
b. Another series of experiments with lasers is found here: . Although the source is Cornell, the intro addresses what seem to be high school standards. This pdf contains photos and teacher materials to help with set-up of the experiments.
5. If you want to discuss the science behind the laser, International Fiber Optics, the maker of Metrologic lasers, has an old version of their experiment book, “Experiments Using a Helium-Neon Laser” available online. The early part of this pdf document (pp 12–16) contains good coverage of the entire process of laser light generation, including pumping, population inversion and electron energy levels. ()
6. Semiconductor laser diodes involve the use of various semiconductors. When discussing the periodic table, you can show how elements in column 14 and its two neighbor columns on either side can become conductive. You can illustrate the effect of adding dopants to these elements making them electrical conductive by using an analogy. Pure water doesn’t conduct electricity (and you can show this with a conductivity tester. Yet when we add just a pinch of salt to the pure water, it conducts extremely well. The same is true of adding dopant to an element of the aforementioned columns of the periodic table. ()
7. Here is a YouTube video (NSF?) that simulates normal light vs. laser light using students moving, either randomly or in sync: .
8. A two-part YouTube video lecture (~29 minutes total) (in the format of the Kahn Academy videos, with a black screen and colored writing developing with the lecture) shows how the He-Ne laser works. It discusses the electron energy level jumps and population inversion. ( and )
9. It might be interesting to show students a LED bulb by itself and light it with a 9-volt battery. You can purchase single LEDs very inexpensively at Radio Shack stores. You can demonstrate to students that the LED will light when the leads are connected to the battery terminals, but when you reverse the leads, the LED won’t light (hence, semi-conductor).
10. You can show students that laser beams are invisible in ordinary air by shining a laser across the room. They will see it as it hits the wall or whiteboard, but not its path to get there. Make sure they are looking perpendicular to the beam’s path. If you create smoke or dust in its path, the laser beam then becomes visible as the particles in its path deflect some of the photons in the beam. The same effect can be seen by shining the laser through pure water or a clear solution. They won’t see the beam’s path. Then add something that will make a colloid, like a few drops of milk or a bit of fine powder. The beam will now be visible through the liquid as the particles again deflect the beam. Both the dust in the air and the particles that make the water a tad cloudy are examples of colloids, and the visible beams are examples of the Tyndall effect.
Out-of-class Activities and Projects
(student research, class projects)
1. Progress in developing a new technology often is inhibited by the need for supporting science and technology that does not yet exist. Students might want to research the history of lasers in light (no pun intended) of this statement and share that knowledge with their classmates.
2. If you don’t have much class time for the study of lasers, you might want to assign students to visit this Web site to learn on their own about lasers: . It provides a dialogue between a student and teacher, and it has animations along the way to help students understand the science behind the content. In fact, if you go back to the table of contents for this site, , you’ll find a lot of interactive information pages about atoms, electrons and light.
3. Students can research the various types of lasers and their applications, and try to determine what properties of that specific laser make it useful for that particular purpose.
4. Research is now being conducted on the medical applications of laser diodes. They have both advantages and disadvantages compared to the use of genuine laser beams. Students might research and report on some of these medical applications, as well as the advantages and disadvantages of using laser diodes (sometimes called super luminescent light-emitting diodes) as opposed to classical lasers. (Teacher’s Guide for April 2001 ChemMatters, Graham, T. Light-Emitting Diodes—Tune in to the Blues. ChemMatters 2001, 19 (2), pp 4–5)
References
(non-Web-based information sources)
[pic]
The ChemMatters article “Fireworks in the Smokestack” discusses laser spark spectroscopy and how lasers help scientists detect various metal pollutants as they leave smokestacks of modern incinerators, both municipal and industrial. Author Scott draws an analogy between the colors and spectra of fireworks, which are due primarily to the metal atoms’ electron excitations and the similar effects caused by laser impact. (Scott, D. Fireworks in the Smokestack. ChemMatters 1996, 14 (1), pp 8–9)
This article describes the chemistry behind light emitting diodes—some of the main lasing mediums in semiconductor diode lasers: Graham, T. Light-Emitting Diodes—Tune in to the Blues. ChemMatters 2001, 19 (2), pp 4–5.
The ChemMatters Teacher’s Guide to the April 2001 issue includes background information for teachers concerning p and n type semiconductors and the p-n junction. It also describes how to create a laser using a light-emitting diode, and the probability that LED lights will eventually replace incandescent light bulbs (which they already are doing).
This issue of ChemMatters contains a good article on the chemistry of tattoos, including mention of removal by laser surgery: Rohrig, B. Tattoo Chemistry Goes Skin Deep. ChemMatters 2001, 19 (3), pp 6–7).
The ChemMatters Teacher’s Guide to the October 2001 issue includes a little more detail about what is involved in removal of tattoos, from the early days of sanding away surface layers of skin to dermabrasion to laser removal. Interestingly, the ChemMatters issue contains two articles that contain references to lasers and the Teacher’s Guide to this issue contains three articles that have references to lasers.
“Trolling the Seas for New Medicines” describes the search by pharmaceutical companies to find new medicines from aquatic life. Cancer is obviously a disease they’d like to focus on when finding new plant/animal life for drugs. (Black, H. Trolling the Seas for New Medicines. ChemMatters 2001, 19 (4), pp 6–7)
The ChemMatters Teacher’s Guide for the December 2001 issue (above) includes background information for teachers concerning two “new” anti-cancer drugs being developed from marine life—sea squirts to be precise.
Check out the “Question from the Classroom” in the December 2002 issue of ChemMatters. In this feature author Becker discusses how CD players and burners work, including the role the semiconductor diode laser plays in playing the music. (pun intended).
(Becker, R. “Question from the Classroom”, How Do CD Players Work? ChemMatters 2002, 20 (4), p 2)
In “Nanotechnology: World of the Super Small” the author discusses what nano means, and applications of nanotechnology, including “cooking up a new drug delivery system with viral capsids that just might be able to carry potent anti-cancer drugs directly to the tumor site.
(Rosenthal, A. Nanotechnology: World of the Super Small. ChemMatters 2002, 20 (4), pp 9–13)
In this “Question from the Classroom” in the April 2003 issue of ChemMatters, Bob Becker discusses how lasers work and why they’re “special”. (Becker, R. “Question from the Classroom”, How do lasers work and what is so special about laser light? ChemMatters 2003, 21 (2), pp 2–3, )
The April, 2003 ChemMatters Teacher’s Guide includes useful background information for teachers about lasers.
Author Rohrig discusses cryogenics in this ChemMatters article. Among other uses for cryogenics, scientists have applied it to cryosurgery to battle cancer, both on the skin and within the body. (Rohrig, B. Cryogenics: Extremely Cold Chemistry. ChemMatters 2004, 22 (1), pp 14–16, )
In the “ChemSumer” section of this issue of ChemMatters “Battling Zits” tells the story of teenage angst. But it includes a little bit about laser surgery, including wavelengths of laser emission and what laser beams do to acne. (Baxter, R. “ChemSumer”, Battling Zits. ChemMatters 2005, 23 (2), pp 4–6, )
In this article about digital photography and printing, author Rohrig discusses the roles semiconductors and lasers play in both devices. (Rohrig, B. The Chemistry of Digital Photography and Printing. ChemMatters 2006, 24 (1), pp 4–7, )
Web sites for Additional Information
(Web-based information sources)
More sites on the history of the laser
The Laserfest Web site, a celebration of 50 years of laser development (1960–2010), contains a timeline of laser science milestones at . You can drag the cursor across the screen to view discoveries that happened at various times, from 1900 to 2009. Clicking on any of the discoveries provides more information about that event.
Here’s another slide-the-cursor timeline from Photonics Media: . This timeline begins at 1950.
The Nobel Prize Web site contains a Laser Challenge game for kids (middle school, maybe) that asks them to answer questions about uses and history of lasers. They can get points in a game format: .
More sites on laser science
For more information about lasers—how they work, how they were developed, types of lasers and their uses, as well as a list of links to other laser sites, see the EnglishInfo! (yeah, I know sounds improbable) Web site at .
For detailed information on lasers visit the RP Photonics Web site, “Encyclopedia of Laser Physics and Technology” at An alphabet at the top allows you to search for an item by clicking on the first letter of the item.
Here is a detailed discussion of how excimer lasers work, from Photonics Handbook: , It includes diagrams and microphotographs.
Laser Fundamentals provides more detail about how a laser works and gives descriptions of several different types of lasers:.
Wikipedia has a good Web page on the He-Ne laser at .
More sites on uses of lasers
The Web site contains this page about LG’s new (2013) 100-inch laser projected television about to go on display: . Dubbed the “hecto-laser” TV, it can be ceiling-mounted only 22 inches from the screen/wall. (Hecto is the prefix for 100.)
These videos show commercial television stations covering the progress of the U.S. National Ignition Facility (NIF):
CBS Sunday Morning News, which did not view NIF in a very favorable light: , and
BBC’s segment (250 half-reactions), visit the Wikipedia site at .
More sites on lead-acid storage batteries
The Hyperphysics site contains some nice drawings of the lead-acid battery, along with the chemical reactions occurring therein. View these at . Note that current is shown as traveling opposite the flow of electrons, as is usually the way physicists do it.
The US Department of Energy (US DOE) published a “Primer on Lead-Acid Storage Batteries”. It contains a few diagrams of the battery as well as the chemical equations describing the charge/discharge cycles. Internal hyperlinks help you navigate through the document. You can download a pdf of the document here: .
For a detailed description of the basics of lead-acid batteries, visit this Web site from “autoshop 101” .
UStudy’s Web site provides almost 100 links to other sites related to lead-acid batteries. ()
Here’s a < 3-minute video that describes the manufacture of lead-acid batteries: . It was originally from How Stuff Works, but it is no longer on their Web site.
Here is a 5-minute video on the lead-acid battery that shows the construction of the battery and how it works, and it discusses engineering difficulties in designing batteries to replace the lead-acid battery. ()
More Web sites on Teacher Information and Lesson Plans
(sites geared specifically to teachers)
This Word document, geared for middle school (grades 6-9), offers for teachers a complete two-week curriculum on electrochemistry that includes several lab activities and a culminating project. It provides teacher materials as well as student material and is replete with standards, although they are Washington state standards. It uses the 5E approach to teaching/learning. ()
Is Your Car a Living Thing?
Background Information
(teacher information)
The article compares the fuel-engine-exhaust system in an automobile to the digestive system in humans. The major point of comparison is that in both humans and cars the food and fuel respectively are made up of larger molecules which are broken down for use in both systems. Noting that petroleum, the source of fuel for cars, is a mixture that includes larger molecules, and that foods are made up of large molecules like fats, carbohydrates and proteins, the article details some of the chemical processes that foods and fuels go through as they are used.
It should be obvious to students that a car is not a living thing, but it might be worth reviewing with students the characteristics that identify something as living. They include:
• A level of complexity that includes cells-tissues-organs-organ systems-living organism
• Metabolism that transforms chemicals from the environment into useful substances and energy
• Ability to respond to stimuli in the environment and to alter behavior based on the stimuli
• Ability to move on its own
• Ability to grow by transforming material from the environment into matter like itself
• Can produce copies of itself in a reproductive process
• Can adapt to external environment and evolve
• Ability to influence living things around it.
So, although cars and people are similar in several ways described in the article, cars are not living organisms. Nevertheless, the comparisons in the article are interesting. The general approach in the following sections of this Teacher’s Guide is to provide details on the chemicals and processes on both sides of the comparison—fuels and foods.
More on gasoline
Much of the material that follows on gasoline has been adapted from the October, 2008, Teacher’s Guide for the Olympic Flame article.
Petroleum, from which gasoline is produced, is a mixture of hydrocarbon compounds. The simplest series of hydrocarbon compounds—those made up exclusively of carbon and hydrogen—is called the alkane series. The carbon and hydrogen atoms in all of the compounds in this series are bonded with single bonds. Such compounds are known as saturated compounds (the compound has no double bonds).
Since we know that in covalent bonding each carbon atom has a bonding capacity of four, the simplest hydrocarbon has a formula of CH4 (methane). If there is one C-C bond, then the formula will be C2H6 (ethane). The third alkane hydrocarbon has a formula of C3H8 (propane), the fourth, C4H10 (butane) and the fifth, C5H12 (pentane). In general the alkanes fit into a general formula of CnH2n+2. Beginning with pentane, the names of the rest of the compounds in this series add a prefix to the –ane ending: pent-, hex-, hept-, oct-, non-, dec-, etc.
These hydrocarbon compounds are all found in either natural gas or petroleum or both. The individual compounds are separated from the natural petroleum mixture during the refining process (see below). The individual hydrocarbon compounds or mixtures of them can be used as fuels like gasoline, which is a mixture of primarily C5 to C12 alkanes.
Your students will be interested in how this relates to the discussion of petroleum and gasoline. Gasoline is produced by fractionally distilling petroleum (or crude oil), which is a mixture of hydrocarbons, and then remixing some of the individual hydrocarbons to make the gasoline, which is itself a mixture. The chart below shows the range of hydrocarbons that make up commercial products which are derived from petroleum.
Refining Fraction Boiling Point (oC) Number of Carbon Atoms
Natural gas less than 20 C1 to C4 (methane-butane)
Petroleum ether 20-60 C5 to C6
Gasoline 40-200 C5 to C12
Kerosene 50-260 C12 to C13
Fuel Oils above 260 C14 and above
Lubricants above 400 C20 and above
Crude oil—petroleum—cannot be used as a fuel in its natural state. Remember that crude oil is a mixture of hydrocarbons, and these are separated from each other in a refinery like the one pictured at right. The petroleum mixture is heated in a furnace and the liquid components boil off according to their boiling points, lowest first. The vapors are allowed to rise in the refining tower and condense back to liquid form and are then drawn off. Each liquid distillate has its own boiling point, which allows the components to be separated. The process is called fractional distillation. The liquids are then remixed to produce the products ()
listed above.
Gasoline is made from petroleum in several steps. Gasoline as such does not exist in crude oil. Rather, crude oil is mostly made up of larger hydrocarbons, like pentadecane (C15H32) for example. "Cracking" is a method by which these large hydrocarbon molecules are broken down into the lighter hydrocarbons that make up gasoline. There are two kinds of cracking, catalytic and thermal. Catalytic cracking is the preferred method of making gasoline because it requires lower temperatures (making the method cheaper) and because it produces better gasoline. Catalytic cracking makes use of zeolite catalysts, which are aluminosilicate materials, to break down large hydrocarbons at temperatures of around 500ºC and at pressures of around 13 atmospheres. Not only are large hydrocarbon molecules broken down into smaller ones in this process, but linear alkanes are rearranged into highly branched ones, or into aromatic molecules like benzene and toluene. By contrast, thermal cracking requires much higher temperatures (around 700ºC) and produces mostly linear alkanes, which make poorer fuels than branched alkanes and aromatic hydrocarbons. The source of the large hydrocarbon molecules is often the naphtha fraction (10-12 carbons) or the gas oil fraction (10-70 carbons) from the fractional distillation of crude oil. There are many reactions that occur during cracking, but below is an example using the hydrocarbon C15H32:
C15H32 ( 2 C2H4 + C3H6 + C8H18
ethene propene octane
In this reaction octane is the desired product and can be mixed with other alkanes to increase the gasoline yield in the refining process. A simulation of the cracking of hexane is shown here: .
According to American Chemical Society’s National Historic Chemical Landmark Web site,
The first full-scale commercial catalytic cracker for the selective conversion of crude petroleum to gasoline went on stream at the Marcus Hook Refinery of Sun Company (now Sunoco, Inc.) in 1937. Pioneered by Eugene Jules Houdry (1892-1962), the catalytic cracking of petroleum revolutionized the industry. The Houdry process conserved natural oil by doubling the amount of gasoline produced by other processes. It also greatly improved the gasoline octane rating, making possible today’s efficient, high-compression automobile engines.
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To summarize: the fuel for automobiles begins as petroleum, a mixture of compounds, some of which are too large to be of use in a liquid fuel. So the compounds in the petroleum mixture are separated from each other via distillation in a refinery, thus isolating the smaller molecules that can be remixed to form gasoline. In addition, in the refining process some of the larger molecules are broken apart in the cracking process so that they too can be remixed to form gasoline. Both of these processes confirm part of the article’s claim that in the automobile it is important that more complex molecules are broken down into simpler molecules that are suitable for use as a fuel.
More on food and digestion
The “complex-to-simpler” theme of the article is carried through to digestion in the human body. The article says that food, like petroleum, has to be processed prior to use. The article also says that the food that is taken into the body is made up of nutrients which are complex molecules like carbohydrates, fats and proteins. The next section of the Teacher’s Guide, then, takes a look at the chemicals involved in digestion. Much of this section has been adapted from the April, 2006, Teacher’s Guide to the article “The Dog Ate My Homework and Other Gut-wrenching Tales.”
Digestion in humans takes place in stages and in each stage more complex molecules are broken down into simpler ones. Digestion begins with chewing. This results in a large increase in surface area of the food, so that enzymes can be more effective in the actual chemistry of digestion. In addition to breaking down the food, chewing mixes in saliva, which helps to lubricate the food. Swallowing moves the lubricated food into the esophagus, on its way down to the biochemical reactions of the digestion process in the stomach and beyond.
The food ingested by humans consists of many different molecules, but the bulk of them are huge macromolecules that cannot be absorbed by cells in the body. Here’s a look at the three main groups of macromolecules involved:
Proteins are long chains (polymers) of amino acids linked together by peptide bonds. Generally, proteins must be broken down chemically into individual amino acids in order for them to be absorbed through the cells in the lining of the stomach. Proteins can be hydrolyzed into peptides by proteases; peptides can then be further broken down into amino acids by peptidases. Both enzymes break peptide bonds.
Lipids include fatty acids, neutral fats, waxes and steroids. Most important for this article are fatty acids, which are the building blocks of many complex lipids. Fatty acids are chains of carbon atoms, 14–22 carbon atoms long, ending in a carboxylic acid. They usually have even numbers of carbon atoms. Their differences lie not only in the number of carbon atoms, but also in the positions of the double bonds that make them unsaturated.
Triglycerides are the most abundant storage form for fat in animals and plants, and are, therefore, the most important dietary lipid. A triglyceride molecule is made of one glycerol molecule (in red at right) attached at each of its three carbon atoms to different fatty acids through ester bonds (see structure at right). These triglycerides are very large molecules that cannot be absorbed. They must be broken down by the enzyme pancreatic lipase into a monoglyceride and two separate fatty acids, all three of which are able to be absorbed by the body. Other lipases are able to hydrolyze triglyceride into three separate fatty acids and a glycerol molecule.
Carbohydrates are aldehydes or ketones derived from polyhydric alcohols, primarily penta- and hexahydric alcohols. Carbohydrates can be broken down into three major groups: monosaccharides, disaccharides and polysaccharides.
Monosaccharides are the simple sugars, mostly hexoses, like glucose, and fructose, or pentoses, like ribose. These are typically produced by the breakdown of more complex carbohydrates, and these are easily absorbed and transported across the wall of the digestive tract and into the bloodstream.
Disaccharides are simply two monosaccharides that are linked together by a glycosidic bond. Common disaccharides are sucrose, lactose and maltose.
Polysaccharides are large polymers made up of smaller sugars, primarily glucose. They are the most abundant carbohydrate food group in most animals. This portion of carbohydrates can be further subdivided into three main groups: starch, cellulose, and glycogen.
In order for humans to use these nutrients they must be all broken down into their simplest form. Carbohydrates are digested most easily. Sugars are the first of the major nutrients to be digested, beginning in the saliva and continuing in the stomach and small intestine. Starches, the other major carbohydrate class, are digested in two steps. Enzymes in saliva and pancreatic juice break starch into maltose, and maltose molecules are broken down to glucose in the intestines. Digestion of proteins begins in the stomach where they are broken down into peptide units. These are broken down to amino acids in the intestines. Fats are most difficult to dissolve because they are not water soluble. In the intestines fats are emulsified by bile acids and broken down by enzymes into fatty acids, glycerol and cholesterol.
More about enzymes
This section on enzymes is included here because enzymes are biological catalysts. The article has a section on catalytic converters and the liver, and it emphasizes the importance of the catalyst in processing waste chemicals. Even though the article does not mention catalysts that are used in the petroleum cracking process, these catalysts are referenced above (see “More on gasoline”). You can point to these examples to illustrate to students the role that catalysts play in many types of chemical reactions, including the chemistry of digestion.
The major enzymes involved in digestion are: proteases, lipase and amylase, hydrolyzing proteins, fats, and starches, respectively. A good Web site to learn more about the actions of these enzymes can be found at . A diagram at that site shows a visual representation of the breakdown of a protein to peptides by trypsin and chymotrypsin.
Most chemical digestion of food actually happens in the small intestine, where the above enzymes are delivered primarily by the pancreas. The liver also plays a pivotal role in digestion as it secretes material into the small intestine—mainly bile acids. These, however, act primarily to emulsify and solubilize lipids so that pancreatic enzymes can act on them chemically to hydrolyze them into fatty acids and monoglycerides, both of which can be absorbed through cell membranes. Without bile acid emulsification of lipids, the fat globules are too large for enzymes to efficiently carry out hydrolysis—the enzymes can only reach the lipids that are on the surface, the outside of the globule. The interior of the globule would never be broken down into usable fatty acids.
More on energy in cars
The basic principle of an internal combustion engine (ICE) is to combine a chemical compound in which a relatively large amount of energy is stored with air in a closed cylinder and ignite the mixture to release the energy that results from the combustion. In the modern automobile engine there are four operating phases, as illustrated in the diagram in the article and in the diagram below. Note that the diagram below, as well as the one in the article, shows one engine cylinder as it would look in the four stages or strokes. In modern cars there are multiple cylinders—fours, six or eight—operating in concert.)
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Internal combustion takes place inside a metal cylinder which has a piston which moves up and down inside it. In the first phase at left in the above diagram—a downward piston stroke—air and fuel are taken in to the cylinder in the induction or intake stroke. The piston moves upward in the cylinder in the second phase to compress the air-fuel mixture. The third phase, the power stroke, is initiated by a spark from a spark plug at the top of the cylinder. The spark provides the activation energy to begin the combustion of the air-fuel mixture. The combustion is exothermic, and as a result the exploding gas mixture forces the gas mixture to expand and, in turn, forces the piston downward to complete the third phase. As the piston moves upward once again in the fourth phase the gaseous products of the combustion are forced out of the cylinder via a small piston that opens and closes.
You may already have studied types of reactions, including combustion, like the example below using octane as the fuel:
2 C8H18 + 25 O2 ➙ 16 CO2 + 18 H2O + energy
Recall from earlier in this Teacher’s Guide that gasoline is actually a mixture of hydrocarbons so the reaction shown for octane is only an example of ICE chemistry. In general the stoichiometry of the ICE combustion requires an ideal air to fuel ratio of 14:1. At that ratio the engine gives maximum performance with minimum reaction by-products. It is most important to note that the reaction is exothermic. The energy produced is the energy needed to move the car, as the article notes. The heat produced in the explosion, or rapid combustion, causes the gases in the cylinder to expand and drive the piston downward, turning the driveshaft that is attached.
You might want to note that during two of the four cycles the behavior of the gas mixture in the cylinder can be described by one or more of the gas laws. In only two of the four strokes—compression and power—can the piston-cylinder setup be considered a closed system, therefore containing a fixed amount of gas. Since it is a mixture of gases, Dalton’s Law of partial pressures applies. During the compression stroke the volume of the gases is greatly decreased. Boyle’s Law applies here. The pressure of the gas molecules on the piston is now greatly increased. As the spark is produced at the beginning of the power stroke, the gas mixture undergoes rapid combustion (that is, it explodes) and the heat produced raises the temperature of the gases. This serves to increase the pressure they exert according to Amontons’ (Gay-Lussac’s) Law, and this pressure does work on the piston, driving it toward the crankshaft, delivering power eventually to the wheels of the car.
There are several energy conversions in an ICE. The chemical potential energy of the fuel is converted to thermal energy and then to the desired mechanical energy to move the car. However, ICEs are very inefficient. Only about 20 per cent of the energy released by combustion is actually converted to useful motion. The other 80 per cent is lost as heat, friction or drag. The chart below shows more detail about energy losses in an ICE.
More on energy in the body, including mitochondria
Energy for the human body is produced primarily by aerobic respiration. As the article suggests, the chemistry of this process using the carbohydrate glucose as the food nutrient occurs in multiple steps but in summary looks like this:
C6H12O6 + 6 O2 ➙ 6 CO2 + 6 H2O + energy
Glucose oxygen carbon water
dioxide
Note first that glucose is already the product of a catabolic chemical process in which a more complex carbohydrate like sucrose (C12H22O11), a disaccharide composed of glucose and fructose, has been broken down by enzyme action in the stomach. The article emphasizes the fact that both in automobiles and humans, larger, more complex molecules are broken down into simpler molecules. Also note that aerobic respiration, like combustion in an automobile, is exothermic. The energy produced is the energy needed for humans to function. The major differences between the two reactions is that cellular respiration takes place at a lower temperature and occurs in multiple steps, thus producing energy at a much slower rate than in automobile combustion.
As noted above, the breakdown of glucose into carbon dioxide (exhaled with the breath) and water (eliminated as urine, exhaled water vapor or perspiration) is a multi-step process, and that process occurs primarily in the mitochondria of human cells. All cells in humans contain mitochondria (the singular is “mitochondrion”). They are organelles whose primary function is to generate energy by breaking down glucose or other nutrient molecules and in the process, storing energy in molecules of adenosine triphosphate (ATP). Different cells have varying numbers of mitochondria, from just one to several thousand, depending on the specialized cell function. For example, a nerve cell may have relatively few mitochondria, whereas a muscle cell with its high energy requirement will have hundreds or thousands. Mitochondria are unique organelles in that they have two membranes. One covers the outside of the organelle completely and the other is a highly folded membrane that greatly increases the inner surface area of the organelle. These folds, called cristae, make up the surface area for the chemical reactions that are part of cellular respiration. Mitochondria, therefore, are structured so as to do the maximum chemical work possible. Mitochondria range in size from 0.5 to 1.0 µm. See the diagram below.
The major respiration steps that take place begin with the glycolysis of glucose to form pyruvic acid, CH3COCOOH, NADH, a coenzyme, and adenosine triphosphate, ATP. This step takes place outside the mitochondria in the cell cytoplasm and yields a limited amount of energy. The pyruvic acid anion, referred to as pyruvate, is passed into the mitochondria and is the reactant in the Krebs (or citric acid) cycle which produces high-energy electrons which, as the article describes, are transported through multiple oxidation-reduction reactions by NADH. This process produces up to 30 additional ATP molecules, which store energy produced in the process. The ATP molecules are transferred to sites where energy is needed and are converted back to adenosine diphosphate, ADP. In the release of one phosphate group from ATP and the bond-forming step that results in ADP the energy once stored in the ATP is released to biochemical work in the cell. The ADP/ATP process is reversible, much like a rechargeable battery. ADP is recycled back into the mitochondria to be used to synthesize more ATP. Also, at the end of the electron-transfer process some electrons have lower energy and are added to oxygen which, in turn, forms the water that we recognize as one of the products of cellular respiration.
Although not directly related to the energy focus of the article, mitochondria are important for multiple reasons. The United Mitochondrial Disease Foundation says this about the importance of mitochondria:
The conventional teaching in biology and medicine is that mitochondria function only as "energy factories" for the cell. This over-simplification is a mistake which has slowed our progress toward understanding the biology underlying mitochondrial disease. It takes about 3000 genes to make a mitochondrion. Mitochondrial DNA encodes just 37 of these genes; the remaining genes are encoded in the cell nucleus and the resultant proteins are transported to the mitochondria. Only about 3% of the genes necessary to make a mitochondrion (100 of the 3000) are allocated for making ATP. More than 95% (2900 of 3000) are involved with other functions tied to the specialized duties of the differentiated cell in which it resides. These duties change as we develop from embryo to adult, and our tissues grow, mature, and adapt to the postnatal environment. These other, non-ATP-related functions are intimately involved with most of the major metabolic pathways used by a cell to build, break down, and recycle its molecular building blocks. Cells cannot even make the RNA and DNA they need to grow and function without mitochondria. The building blocks of RNA and DNA are purines and pyrimidines. Mitochondria contain the rate-limiting enzymes for pyrimidine biosynthesis (dihydroorotate dehydrogenase) and heme synthesis (d-amino levulinic acid synthetase) required to make hemoglobin. In the liver, mitochondria are specialized to detoxify ammonia in the urea cycle. Mitochondria are also required for cholesterol metabolism, for estrogen and testosterone synthesis, for neurotransmitter metabolism, and for free radical production and detoxification. They do all this in addition to breaking down (oxidizing) the fat, protein, and carbohydrates we eat and drink.
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On balance the ChemMatters article compares two variations of a chemical process that can be summarized as:
Food/Fuel + Oxygen ➙ Carbon dioxide + Water
In the case of a car, the process is designed to occur explosively at high temperatures yielding large amounts of energy quickly. And in humans the process takes place at body temperature and in a series of slow steps to produce energy at a rate the body can use.
More on engine waste (include catalytic converter)
In theory, only carbon dioxide and water should emerge from the exhaust system of an automobile. However, due to actual operating conditions in most cars, other compounds are also present. Some engines do not burn all of the hydrocarbons in gasoline and so these gases are part of the waste stream. If the combustion is incomplete due to an insufficient supply of oxygen to the cylinder, then carbon monoxide is produced in combustion along with carbon dioxide. High operating temperatures of many modern cars causes nitrogen to react when it would be unreactive at lower temperatures. As a result oxides of nitrogen are also part of the exhaust gases.
For all of these reasons catalytic converters were introduced in cars in 1975. The converter is contained in a stainless steel housing. The converter itself is made up of either a fine mesh structure or a honeycomb ceramic structure whose purpose is to provide maximum surface area on which the chemical reactions can take place. The surfaces of the converter are coated with an aluminum oxide wash that adds to the surface area. And on this surface is embedded one of the typical metal catalysts—either platinum, palladium or rhodium. The mass of these metals in a single converter is very small, less than 10 grams. At this writing the price of palladium is $705/oz. (that’s $24.87/g), rhodium is $1150/oz. and platinum is $1525/oz. so the theft of converters is a chronic problem.
Most modern converters are three-way converters. That is, they oxidize waste carbon monoxide to carbon dioxide, they reduce oxides of nitrogen to nitrogen and oxygen gases and they oxidize unburned hydrocarbons to carbon dioxide and water.
The three reactions look like this:
Reduction of nitrogen oxide: NOx → N2 + O2
Oxidation of carbon monoxide: CO + O2 → CO2
Oxidation of hydrocarbons: CxH4x + 2x O2 → x CO2 + 2x H2O
In the converter the conversions take place in series. First, platinum and rhodium catalysts reduce the nitrogen oxides in the waste stream. If we use NO2 as an example, we see that the oxygen is removed from the NO2. Two single nitrogen atoms combine to produce diatomic nitrogen along with the diatomic oxygen that is produced. The oxygen that is produced is then used in the oxidation of unburned hydrocarbons and carbon monoxide. This second step is catalyzed by a platinum-palladium catalyst. In these processes the atoms involved are actually held temporarily loosely in place by the catalysts so that the reactions can occur.
Note that all three reactions in stage 1 and 2 are redox reactions, and that the metal catalysts facilitate the exchange of electrons in these reactions. You may want to review (or preview) oxidation and reduction reactions with your students, noting to them that oxidation is loss of electrons and reduction is the gain of electrons. For example, again using NO2 as an example, we see that the oxidation number of nitrogen in NO2 is +4, where the oxidation number of nitrogen in N2 is 0. The oxidation number moves in a negative direction (+4 → 0) and so we can say that the nitrogen has gained electrons; that is, it is reduced. So stage 1 of the converter is a reduction process. At the same time the oxidation number of the oxygen in NO2 is -2, and in O2 it is 0, moving in a positive direction (-2 → 0), indicating that oxygen has lost electrons (it is oxidized).
The third phase in a converter is an oxygen sensor which monitors the volume of oxygen in the waste stream. It can signal the car’s computer to adjust the air to fuel ratio in the cylinders, keeping it near the 14.7 to 1 ratio mentioned earlier. This also insures that there is sufficient O2 coming to the converter to oxidize unburned hydrocarbons and carbon monoxide.
Catalytic converters were first required following the Clean Air Act of 1970. By 1975, the EPA had regulated the permitted amount of exhaust pollutants, and in order to meet these new regulations catalytic converts were required on cars. An added benefit to the advent of converters was the removal of lead from gasoline since lead would deactivate the catalytic converters. Current three-way converters came on the scene in 1980–81. The Clean Air Act of 1990 further strengthened control of exhaust emissions. The catalytic converter was invented in the early 1950s by Eugene Houdry, originally not for cars but for factory smokestacks. (See “More on gasoline”, above, for additional information on Houdry). Later in the 1950s Houdry began to research how to adapt the smokestack converter for use in cars. The modern three-way converter was developed by John J. Mooney and Dr. Carl D. Keith working at the Engelhard Corporation (now a division of BASF Catalysts).
More on body waste (liver)
The article points to the human liver as the organ comparable to the catalytic converter in cars, and in some ways it is. The liver performs hundreds of functions in the body and removing toxic substances is just one of them. And, as the article says, enzymes in the liver catalyze the detoxification processes. Some of the harmful substances are the result of normal biochemical reactions in the body, but most are brought into the body from the environment. Examples of external toxins include viruses and bacteria, medications and drugs, food additives and preservatives, food colorings, artificial sweeteners, insecticides and residue from fertilizers used in agriculture, volatile organic compounds and air pollutants.
The liver detoxifies the body in three ways. It filters toxins from the blood, produces bile and breaks down toxins, chemically using enzymes as catalysts. The liver is suspended behind the ribs on the upper right side of the abdomen and spans most of the width of the body over to the heart. It receives blood directly from the stomach, pancreas and intestines via the hepatic portal vein. Its intricate web of specialized cells filters larger toxin molecules from the blood at a rate of two quarts of blood per minute. Within its cells are hexagonal arrangements of veins that funnel blood through a web-like structure that filters out toxins and drains the purified blood into a central vein which sends the blood to other parts of the body (see diagram at right).
The second way the liver purifies the body is by producing bile. Many of the toxins that enter the body are fat soluble which means they dissolve only in fatty or oily solutions and not in compounds. Bile emulsifies fat molecules, thus creating increased surface area for enzymes to break down the fat molecules quickly to a water-soluble form so that they can be absorbed into the intestines.
The third purifying process is more involved and extensive. It is the two-step process described in the article. In phase 1 the liver modifies the toxin molecule either by neutralizing it completely or by modifying it via oxidation, reduction or hydrolysis so that it is less toxic, resulting in an intermediate product which will be further modified in phase 2. The second phase is called the conjugation phase because the intermediates from phase 1 are reacted with compounds that make the toxin water-soluble so that it can be excreted in urine. These two phases take place in liver cells, specifically in the smooth endoplasmic reticulum of the cell, which is rich in enzymes. One such enzyme is the cytochrome p450 enzyme, which has the ability to catalyze the oxidation of toxins to make them harmless.
It is interesting to see that both the liver and catalytic converter use catalysts extensively in the chemical changes that take place in them, and that both also do their work in two phases. And while there are three catalysts typically used in a car’s converter, the liver employs hundreds of enzymes to detoxify the range of toxins that enter the blood stream.
Connections to Chemistry Concepts
(for correlation to course curriculum)
1. Distillation—Refineries use this process to separate most major fractions of crude oil from one another. The focus for chemistry class is boiling point as it relates to intermolecular forces.
2. Intermolecular attractions—Boiling points of organic molecules relate directly to their size and surface area in contact with other molecules.
3. Organic chemistry—The chemistry of petroleum and respiration is virtually all organic chemistry.
4. Catalysis—Cracking of larger hydrocarbons into more useful, smaller molecules is done primarily through the use of catalysts to lower the boiling point of the mixture. Unification of smaller molecules into larger ones also involves the use of catalysts.
5. Particle size, surface area and reaction rate—When food is digested, it is broken up into smaller particles that are then able to react with enzymes to actually undergo chemical digestion.
6. Structural formulas—Organic chemistry gives us a chance to show students the varied structures of various hydrocarbon molecules. Also, straight-chain vs. branched-chain alkanes are pertinent here.
7. Types of reactions—Combustion is one of the 5 major types of reactions students study in chemistry.
8. Thermochemistry and heats of combustion—One emphasis in the article is how cars and humans produce energy, mostly in the form of heat.
9. Oxidation-reduction reactions—all of the catalytic converter reactions and some of the mitochondrial reactions involve oxidation-reduction.
10. Biochemistry—All of the reactions related to the human body are biochemical reactions.
11. Gas Laws—The behavior of gases in a car’s cylinders can be described by the gas laws.
Possible Student Misconceptions
(to aid teacher in addressing misconceptions)
1. “Crude oil is the stuff you buy in a can to put in your car engine.” Crude oil is a mixture of hundreds of different hydrocarbon molecules. Engine oil is only a small portion of what’s in crude oil – and a very specific small part at that.
2. “Gasoline is a pure substance—octane.” Gasoline is a complex mixture of hydrocarbons. Even the performance standard, iso-octane, is only one of many compounds found in normal gasoline.
3. “Gasoline is one clean fraction of crude oil that is separated off in fractional distillation.” No, gasoline is a mixture of hundreds of compounds, mostly hydrocarbons. Most are derived from crude oil, but they come from a variety of crude oil fractions and are then mixed in proper proportions to give the properties of gasoline needed for highest efficiency and power output.
Anticipating Student Questions
(answers to questions students might ask in class)
1. “Why can’t petroleum chemists just change all of the crude oil into gasoline? That would keep prices down.” For starters, some molecules in crude oil are too large or too complex to be broken down into gasoline. In addition, we need those other fractions of crude oil for other purposes; e.g., diesel oil for trucks, buses, trains and boats; home heating oil to keep us warm in winter; crude bottoms for asphalt for roads; volatile compounds for solvents; petrochemicals for medicines and plastics; etc.
2. “Why can't liquid gasoline burn?” Combustion is the chemical process of a fuel reacting with oxygen. Fuels burn when their molecules break down, and the atoms in those molecules combine chemically with oxygen atoms. Actually, liquid gasoline DOES burn. But it is a relatively slow process that only burns on the liquid surface because that’s where oxygen from the air can collide--and react--with gasoline molecules. This reaction is not nearly rapid enough to be useful in the internal combustion engine. To make the reaction faster, the fuel injectors in the engine aspirate or atomize the gasoline into very tiny droplets that have much greater surface area than the liquid pool of gasoline in the tank. These small droplets with their greater surface area can react almost instantaneously with oxygen molecules to provide the very rapid reaction—the explosion--mentioned in the “More on energy in cars” section above.
3. “What’s the difference between the term ‘food’ and the term ‘nutrient’?” Products that are grown naturally or produced for human consumption are considered food. As most chemistry students should already know, most foods are complex mixtures of chemical compounds. Some of the compounds—like carbohydrates, fats and proteins—are able to provide energy in the body or can be changed into materials that help the body grow and function. These kinds of compounds are called nutrients. For example, a carrot is a food, but it contains 10 g of carbohydrate and 1 g of protein. The latter are nutrients.
4. “How do catalysts change the rate of a reaction?” They provide the reaction with a new path, not available without them, that has a lower activation energy. The old, now-higher, activation energy is still there, but the preferred path is the reaction with the lower energy.
In-class Activities
(lesson ideas, including labs & demonstrations)
1. On the Royal Society of Chemistry Web site is a video demonstration of catalytic cracking that comes with a pdf of class notes: .
2. PBS has a site on the science of oil at .
3. Students can do a fractional distillation lab in class.
a. A simple procedure that should be done as a demonstration can be found here: .
b. If you have Vernier software, there is another procedure here: .
4. Although the chemical reaction below is not related to any hydrocarbon cracking process, you can present a catalyzed reaction to students using cobalt(II) chloride, Rochelle’s salt, and hydrogen peroxide. Find it at the Flinn Scientific site, .
5. For a NASA unit on combustion see . You may already have combustion labs in your course’s lab manual. Students can test for the products of combustion using limewater and cobalt chloride paper, etc.
6. You can have students compare fuels in a lab activity like this one. This article is primarily about gasoline, but students should understand how different fuels supply differing amounts of energy. ()
7. A series of demonstrations and experiments can be found at this part of the NSTA Scope, Sequence and Coordination Web site, . The demonstrations include genie-in-the-bottle catalysis, digestion of egg proteins (this one’s actually a student experiment), baking bread and yeast, and the enzymes in the liver. These are presented as inquiry-based, student-designed experiments.
8. The Chemical Heritage Foundation Web site contains a section on “Enzyme Specificity” in their “Antibiotics in Action” module. This module contains three experiments that show the digestion of protein, lipid, and starch, respectively. Student and teacher versions of each activity can be found at:
9. This lab provides students experience with various factors such as surface area, temperature and pH affect the rate of a reaction—in this case, the decomposition of hydrogen peroxide, first with MnO2 as a catalyst, and then with catalase from beef liver. It’s called “The Liver Lab”. ()
10. This version “cracker and saliva” lab activity from The Exploratorium suggests that the oft-stated procedure will not work and provides background and a fail-safe procedure to observe the catalytic action of amylase on starch. ()
A variation of this procedure can be found on this University of Georgia site: .
Out-of-class Activities and Projects
(student research, class projects)
1. Students, working singly or in teams, can research each section of the digestive system and produce a class PowerPoint, larger poster, or video that connects each section correctly. Other students or teams of students might research important molecules in the digestive system and include this research into the class production.
2. Students could keep a log of their food intake for a week and then prepare a chart that categorizes the main class of nutrients in each type of food.
3. Students could research the workings of the internal combustion engine and build a model of an ICE with extra credit if the model has moving parts.
4. Student could be assigned the task of interviewing auto mechanics to get their perspectives on the modern internal combustion engines.
5. Revell sells a kit from which you can build a model engine. This might be a worthwhile purchase for students who are tactile learners. ()
References
(non-Web-based information sources)
[pic]
In this article, author Rohrig focuses on carbohydrates in the diet and how they are metabolized. (Rohrig, B. Carb Crazy. ChemMatters 2004, 22 (3), p 6)
This article explains the chemistry of digestion and emphasizes the role of enzymes as catalysts. (Tinnesand, M. The Dog Ate My Homework and Other Gut-Wrenching Tales. ChemMatters 2006, 24 (2), p 4, )
Author Rohrig describes the internal combustion engine and how fuel is burned. (Rohrig, B. Chemistry on the Fast Track: The Science of NASCAR. ChemMatters 2007, 25 (1), p 5, )
This is an excellent article that describes how petroleum is formed, how it is refined and how larger molecules in petroleum are broken down into simpler ones. (Baxter, R. Gold in Your Tank. ChemMatters 2007, 25 (2) p 8, )
Web sites for Additional Information
(Web-based information sources)
More sites on petroleum refining
The American Chemical Society has a Web site that details important events in chemical history. This page is devoted to the Houdry process for cracking petroleum: .
This site discusses the energy needed to break bonds in fractional distillation and shows an illustration of petroleum distillation column: .
This Centers for Disease Control site lists many properties of gasoline: .
This site presents a rather detailed account of the theory behind the process of fractional distillation. It is probably for teacher background only. It also allows you to backtrack in the site to other background pages to help you understand this one. At the end of this page is a diagram of one small part of the petroleum fractional distillation column in more detail, showing the openings and bubble caps in the column, and it gives a description of how the column works. ()
More sites on combustion
This site gives a very technical explanation of combustion kinetics: .
A tutorial on the basic chemistry of combustion is given in the YouTube video .
More sites on digestion
This site from Colorado State University is a comprehensive look at digestion, enzymes and other chemical components. ()
How Stuff Works has a site on digestion including major nutrients, processes, diseases and references for further study. ()
This site from Great Britain details each organ of the digestive system and also includes a video. ()
KidsHealth from Nemours also describes each organ in the digestive system in simple language. ()
The George Matelja Foundation stresses nutritional and digestive health. Along with a lot of background information, this site has a simulation, with explanations, of the digestive process. ()
This site, from the National Institutes of Health “National Digestive Diseases Clearinghouse”, gives a complete review of digestion: .
More sites on mitochondria
For an excellent animated tutorial on how mitochondria function, see .
More is being learned about the functioning of mitochondria and how they are related to disease. See the Mitochondria Research Society at and the United Mitochondrial Disease Foundation at .
The Molecular Expressions site at Florida State University has background information on mitochondria: .
More sites on the automobile
This site has a comprehensive review of the influence of the automobile on America: .
“How Stuff Works” has a Web site that explains internal combustion: .
Lawrence Livermore National Laboratory has a unit studying energy in the internal combustion engine: .
This University of Southern California site provides background on the internal combustion engine, including some history: .
The Ford Motor Company Design Team created a video animation on how an internal combustion engine is built and operates. ()
This page of animated engines includes the internal combustion engine: .
Kennesaw State University produced this ChemCase on Fuels and Society: .
More sites on catalysts and enzymes
This site is the chapter on enzymes from the textbook “The Chemical Basis For Life.” ()
The University of California at Davis has this Web site explaining catalytic converters: .
This lab procedure gives a detailed explanation of how enzymes help to digest carbohydrates, fats and proteins. ()
More sites on the liver
This extensive and detailed Web site explains the biochemistry of the liver.
()
-----------------------
(National Ignition Facility )
1. In an “inverted population” an emitted photon from one atom approaches another atom in which there is an excited electron.
Dropping electron
2. The approaching photon stimulates the excited electron of the neighboring atom to drop. The second emitted photon heads off in the same direction—matching the first one crest for crest. The wavelengths match perfectly!
Coherent light
Excited electron of neighboring atom
Emitted photon
The energy level diagram for helium and neon in a He-Ne laser
()
Microphotograph of cuts made in a human hair by an excimer laser (a demonstration of the precision attainable using this technique)
()
The references below can be found on the ChemMatters
25-year CD (which includes all articles published during the years 1983 through 2008). The CD is ava[pic][?]
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ilable from ACS for $30 (or a site/school license is available for $105) at this site: . (At the right of the screen,
click on the ChemMatters CD image like the one at the right.)
Selected articles and the complete set of Teacher’s Guides
for all issues from the past three years are also available free online
at this same site. (Full ChemMatters articles and Teacher’s Guides are available on the 25-year CD for all past issues, up to 2008.)
Some of the more recent articles (2002 forward) may also be available online at the URL listed above. Simply click on the “Past Issues” button directly below the “M” in the ChemMatters logo at the top of the page. If the article is available online, you will find it there.
The references below can be found on the ChemMatters
25-year CD (which includes all articles published during the years 1983 through 2008). The CD is available from ACS for $30 (or a site/school license is available for $105) at this site: . (At the right of the screen,
click on the ChemMatters CD image like the one at the right.)
Selected articles and the complete set of Teacher’s Guides
for all issues from the past three years are also available free online
at this same site. (Full ChemMatters articles and Teacher’s Guides are available on the 25-year CD for all past issues, up to 2008.)
Some of the more recent articles (2002 forward) may also be available online at the URL listed above. Simply click on the “Past Issues” button directly below the “M” in the ChemMatters logo at the top of the page. If the article is available online, you will find it there.
The references below can be found on the ChemMatters
25-year CD (which includes all articles published during the years 1983 through 2008). The CD is available from ACS for $30 (or a site/school license is available for $105) at this site: . (At the right of the screen,
click on the ChemMatters CD image like the one at the right.)
Selected articles and the complete set of Teacher’s Guides
for all issues from the past three years are also available free online
at this same site. (Full ChemMatters articles and Teacher’s Guides are available on the 25-year CD for all past issues, up to 2008.)
Some of the more recent articles (2002 forward) may also be available online at the URL listed above. Simply click on the “Past Issues” button directly below the “M” in the ChemMatters logo at the top of the page. If the article is available online, you will find it there.
()
Pb(s) + HSO4− (aq) → PbSO4(s) + H+(aq) + 2e− PbO2(s) + HSO4−(aq) + 3H+(aq) + 2e− → PbSO4(s)
+ 2H2O(l)
The total discharge reaction can be written:
Pb(s) + PbO2(s) + 2HSO4− (aq) + 2H+(aq) → 2PbSO4(s) + 2H2O(l) + energy
()
The references below can be found on the ChemMatters
25-year CD (which includes all articles published during the years 1983 through 2008). The CD is available from ACS for $30 (or a site/school license is available for $105) at this site: . (At the right of the screen,
click on the ChemMatters CD image like the one at the right.)
Selected articles and the complete set of Teacher’s Guides
for all issues from the past three years are also available free online
at this same site. (Full ChemMatters articles and Teacher’s Guides are available on the 25-year CD for all past issues, up to 2008.)
Some of the more recent articles (2002 forward) may also be available online at the URL listed above. Simply click on the “Past Issues” button directly below the “M” in the ChemMatters logo at the top of the page. If the article is available online, you will find it there.
()
()
()
()
()
The references below can be found on the ChemMatters
25-year CD (which includes all articles published during the years 1983 through 2008). The CD is available from ACS for $30 (or a site/school license is available for $105) at this site: . (At the right of the screen,
click on the ChemMatters CD image like the one at the right.)
Selected articles and the complete set of Teacher’s Guides
for all issues from the past three years are also available free online
at this same site. (Full ChemMatters articles and Teacher’s Guides are available on the 25-year CD for all past issues, up to 2008.)
Some of the more recent articles (2002 forward) may also be available online at the URL listed above. Simply click on the “Past Issues” button directly below the “M” in the ChemMatters logo at the top of the page. If the article is available online, you will find it there.
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