OBSERVATION OF pH SHIFTS USING THE PROCESS OF IONIC …



OBSERVATION OF pH SHIFTS USING THE PROCESS OF IONIC EXCHANGE

Teri Alvarez-Ziegler

PRIDE High School

Sunnyside, WA

&

Sandra Poisson

Lewis-Clark State College

Lewiston, ID

Washington State University Mentors

Dr. Neil Ivory

Chemical Engineering

&

Ann Marie Hardin

PhD Candidate

Washington State University

Pullman, WA

July, 2006

| |

|The project herein was supported by the National Science Foundation Grant No. EEC-0338868: Dr. Richard I. Zollars, Principal |

|Investigator and Dr. Donald C. Orlich, co-PI. The module was developed by the authors and does not necessarily represent an |

|official endorsement by the National Science Foundation. |

SUMMARY

Overview of Project:

This module is an active learning module, which can be adapted to a teacher’s time schedule and laboratory equipment. The overall focus is to gain an understanding of the effect of ion concentration effect on a changed surface by observing pH shifts that occur during ionic exchange chromatography. The students will also gain a better understanding of such scientific concepts as: Molarity, pH scale, pH indicators, buffers, diffusion, and charged surfaces. Engineering concepts, such as chromatography, are discussed and performed within this lab. These are demonstrative of, and applicable to, the concept and performance of a home water softener system.

Intended Audience:

This teaching module is intended for high school classes, grades 9-12. This module could be used in Biology, Chemistry, or Physical Science classes.

Estimated Duration:

This module is estimated to last a week, based on five 50-minute class periods. Day 1-consists of a pre-test, review of the concepts, worksheets, and discussion. Day 2-the students are divided up into groups of two, as pre-determined by the teacher. The students will prepare the resin needed for the lab. Day 3-the students will make the color standards and stock buffer. Day 4- the students will adjust their buffer to the required NaCl concentrations and perform the resin pH experiment. Day 5-the students compare data/findings. They will also check if all NaCl concentration buffer samples remain at 6.0 pH. They will do their lab write-up and the student evaluation form. Note: The teacher could adjust this module to fit into three block class periods.

INTRODUCTION

Rationale for Module:

The purpose of this module is to expose students to engineering activities. The main focus of this module is to show how the salt concentration affects the surface charge of the resin, and its consequent effect on the pH shift. Students will be able to have hands-on experiences, and develop their laboratory skills. This module will solidify basic scientific concepts in the students as they work on this more complex activity. The students will gain familiarity with proper laboratory procedures, and handling of chemicals and equipment. This module meets various learning standards, see Learning Objectives.

SCIENCE

The following are concepts related to this module:

Molarity (M):

A measurement of concentration. M= moles of solute/liters of solution

pH Scale:

pH= -log[H+], a way to measure the concentration of Hydrogen, and relative acidity or alkalinity. The lower the pH, the higher the Hydrogen concentration is. The pH scale is logarithmic, which means that moving 1 unit either way on the pH scale results in a 10 fold increase in hydrogen ion concentration either direction. The pH scale range is 0 to 14, with 7.0 being neutral. Numbers below 7.0 on the pH scale are acidic. Numbers above 7.0 on the pH scale are basic.

pH Indicators:

These are colored substances that can be either in an acidic or basic form. The acidic and basic forms have different colors. The ranges of different indicators are known and can be found in various literature sources (Brown, LeMay, Bursten, 1997, pp. 579-580). For Bromothymol blue (the indicator used in this module) the active pH range is 6.0 (yellow color) to 7.6 (blue color) (Bishop, 1972, pp. 109).

Buffers:

These are solutions, usually composed of a weak acid or weak base with salts of that acid or base, that resist changes in pH with the addition of an acid or base. The acid form neutralizes the OH- and the base form neutralizes the H+. The buffer effectively stabilizes when the pH of the solution is within ±1.0 of the buffer’s pKa.

If OH- is added to the buffer solution the following reaction takes place:

OH-(aq) + HA (aq) ( H2O(l) + A-(aq)

If H+ is added to the buffer solution the following reaction takes place:

H+(aq) + A-(aq) ( HA(aq)

Buffer capacity: the quantity of acid or base the buffer can neutralize before the pH begins to change drastically.

To calculate the pH of a buffer, use Henderson-Hasselbach equation:

pH= pKa + log ([base]/[acid])

(Brown, LeMay, Bursten, 1997, pp. 624 - 626).

Bis-Tris properties: Useful pH range is 5.8-7.2 and the pKa of the buffer is 6.5 (, 2006).

Diffusion:

This is a process where one substance spreads throughout a space or another substance to reach equilibrium. Diffusion is driven by a difference in concentration across space. Over time, the substance that is not evenly distributed throughout a space will diffuse until an equilibrium condition is reached.

Charged Surfaces:

Positive charges on the surface of materials will attract negatively charged molecules and vise versa (like charges repel each other). The negative molecules will bind to the surface of the positively charged material while positively charged molecules will be repelled from the surface. This is demonstrated by the positively charged resin used in this module. The pH shift is an indication of the exclusion of hydrogen ions from the internal surfaces of the resin.

ENGINEERING

Chromatography:

This is the process of separating substance components (different dyes and/or proteins) based on their differing abilities to adhere to the surface of another substance (Brown, LeMay, Bursten, 1997, p. 9).

Ion Exchange Chromatography:

This process relies on charge to charge interactions between the proteins in a sample and the charges on the resin’s surface (Ion, 2006). The resin used in ion exchange is a matrix composed of small beads, which are made from organic polymers (Ion Exchange resin, 2006). This process can be subdivided into cation exchange, in which positively charges ions bind to a negatively charged resin; and anion exchange, in which the binding ions are negative and the immobilized functional group is positive (Ion, 2006).

The process used in this module is the anion exchange system. The resin used in this module is Q-Sepharose Fast-Flow.

Real Life Application - Home Water Softener Systems:

What is Hard Water?

Hard water is water containing a great deal of the minerals Ca and Mg (both carry a positive charge) (Water Softening FAQ’s, 2006).

Why are people concerned with Hard Water?

Hard water creates soap curd and scale. Soap curds dull the colors of fabrics and shorten the life of the fabric. To get the clothes completely clean, more detergent is needed, which can rack up money (Water Softening FAQ’s, 2006).

Scale is formed when the hard water is heated. This can build up in the pipes forming “rocks.” This causes the water heater to work harder since it has to heat up the rock as well as the water (Water Softening FAQ’s, 2006).

The following are additional problems resulting from hard water: clogged water pipes; water heater inefficiency and scaling; decreased water flow or pressure; frozen valves and faucets; scale spots on glassware and/or silverware; crust rings in toilet tanks and rings in toilet bowl; white spotting on bath tubs, tile, and chrome; white deposits on shower heads; hard to remove film on shower tiles and doors; and poor sudsing of soap and shampoo.

How does the Water Softener Work?

Most water softeners work by using the cation exchange system. This system uses resin beads to remove the Ca and Mg ions from the hard water by the following process. The resin beads attract the positively charged Na or K ions from the saline solution surrounding the beads. The Na or K ions are released when the beads come in contact with the Ca and/or Mg ions in the hard water. The Ca and/or Mg ions will adhere to the surface of the resin beads (Water Softening FAQ’s, 2006).

There reaches a point in the system where all the Mg or Ca have taken up the positions held by the Na or K ions. At this point, recharging the system is required. This is done by adding more salt to the solution which causes the release of the Mg or Ca ions. These ions are released as waste, while the Na or K ions take back their original place, allowing the system to start again (Water Softening FAQ’s, 2006).

What is Soft Water?

Soft water is water with only the Na or K cations remaining. It is the end product of the water softening process. Soft water is a step closer to pure water.

GOALS

Students will use prior knowledge learned from science classes to complete the lab. This teaching module will expand their knowledge and the scope of what their perception of engineering is. Students will learn that engineering involves all aspects of science, and their effects on the world around us.

LEARNING OBJECTIVES

Students will be able to define the following terms (Cognitive; Knowledge):

• Molarity

• diffusion

• pH

• ionic exchange

• ionic exchange chromatography

• chromatography

• pH scale

• pH indicators

• buffers

• charged surfaces

Students will be able to:

1. understand that there are different areas of study in engineering.

( cognitive; comprehension )

2. understand that salt concentration affects the surface charge of the resin.

( cognitive; comprehension )

3. understand what causes the pH shift.

( cognitive; comprehension )

4. have hands-on laboratory experience.

( cognitive; application )

5. develop their laboratory skills.

( cognitive; application )

6. solidify basic scientific concepts.

( cognitive; comprehension )

7. gain familiarity with proper laboratory procedures.

( cognitive; application )

8. gain familiarity with handling of laboratory equipment and chemicals.

( cognitive; application )

Science GLEs:

1. Understand the atomic nature of matter, how it relates to physical and chemical properties, and serves as the basis for the structure and use of the periodic table.

1. Analyze how systems function, including the inputs, outputs, transfers,

transformations, and feedback of a system and its subsystems.

3. Synthesize a revised scientific explanation using evidence, data, and

inferential logic.

4. Analyze how physical, conceptual, and mathematical models represent

and are used to investigate objects, events, systems, and processes.

Reading GLEs:

2. Understand and apply content/academic vocabulary critical to the meaning

of the text, including vocabularies relevant to different contexts, cultures, and communities.

2. Apply understanding of complex information, including functional

documents, to perform a task.

Mathematic GLEs:

3. Understand how to convert units of measure within systems.

3. Apply appropriate methods and technology to collect data or evaluate

methods used by others for a given research question.

6. Apply procedures to solve equations and systems of equations.

2. Apply mathematical tools to solve the problem.

EQUIPMENT

|0.1 M NaOH |Parafilm |

|1 M HCl |pH meter (or pH paper) |

|100 mL beakers |Pipettes or Droppers |

|15 mL Falcon centrifuge tubes w/lids |Q-Sepharose fast-flow, 300 mL or 100 mL |

|50 mL Falcon centrifuge tubes w/lids |Refrigerator unit |

|600 mL beakers |Ruler |

|Bis-Tris |Scale |

|Bromothymol Blue |Small covered containers |

|Calculator |Stir plate w/ magnetic stirrers (or glass stir rods) |

|Distilled (DI) water |Stock bottles |

|Graduated cylinders, 100 mL |Test tube racks |

|Graduated cylinders, 500 mL |Test tubes |

|Graduated eppendorf microcentrifuge tubes |Volumetric Flask, 100 mL |

|Graph paper |Vortex mixer |

|Labels/Tape |Waste beakers |

|NaCl stock |White surface for color comparison (paper) |

TEACHER PREP

Estimated time:

The estimated time for teacher prep is approximately 1 ½ to 2 hours. Of course, this depends on the availability of the materials and equipment needed. This should be enough time to prepare enough material for 5 groups.

Background:

Q Sepharose FF is a positively charged anion exchange resin commonly used in protein purification processes. The positive charge excludes hydrogen and other positively charged ions from the resin phase. The extent of this exclusion is determined by the density of the active surface charges. The resin will be contacted with a 20 mM Bis- Tris buffer at pH 6.0 containing different NaCl concentrations. The chlorine ions in the solution interact with the positively charged resin surface and effectively “turn off” some of the charge sites. This moderates the extent to which hydrogen ions are excluded from the resin phase, and consequently, the magnitude of the pH shift.

Procedures:

Start resin tubes: Total time: 10 minutes for each group.

1. Obtain the stock resin. DO NOT MIX STOCK BOTTLE!

2. Gently stir stock resin while pipetting out 8 mL of settled resin per group, place in 15mL Falcon tube. The goal here is to introduce enough storage alcohol into a region of settled resin to be able pull it into a pipette, not to completely mix the resin with the storage solution.

3. Let the resin settle and adjust to get 4 mL settled resin per tube as follows:

a. If the settled resin volume is too high, add storage solution from the stock bottle to the tube until the liquid volume is equal to the settled resin volume. Invert the tube repeatedly to completely mix the resin and alcohol. Remove resin mixture from the falcon tube until the total volume in the tube is 8 mL. If you have used a clean falcon tube and pipette, the excess can be returned to the stock bottle.

b. If the settled resin volume is too low, repeat step 2 above.

4. Cap tubes and store at room temperature.

5. This should end up equaling 4 mL of settled resin per each group.

Make Bromothymol Blue solution (0.04%): Total time: 20 minutes for whole class.

1. Mix 0.64 mL of 1.0 M NaOH and 0.04 g of Bromothymol blue, in an eppendorf tube.

2. Mix until dissolved, either using a vortex mixer or by inverting the tube.

3. Pour the mixture in a volumetric flask (100 mL).

4. Rinse the eppendorf tube with DI water, until all of the blue solution is removed, placing each rinse in the flask.

5. Fill the volumetric flask to 100 mL with DI water.

6. Mix well.

7. Divide into stock bottles, one for each group.

8. This will be enough for the whole class.

Measure out NaCl: Total time: 25 minutes for each group.

1. Label 4 covered containers with the following [NaCl]: 20 mM, 100 mM, 250 mM, and 500 mM.

2. Weigh out the following amounts NaCl* stock for each group.

20 mM needs 0.1169 g

100 mM needs 0.5844 g

250 mM needs 1.461 g

500 mM needs 2.922 g

3. Place each in the appropriately labeled container.

*Based on 100 mL of buffer at each salt concentration

Measure out Bis-Tris: Total time: 10 minutes for each group.

1. Weigh out 2.0924 g* of Bis-Tris, for each group.

2. Place the Bis-Tris in a covered labeled container.

*Based on 500 mL buffer at 20 mM Bis-Tris

*** We have the teacher weighing the materials due to the probability of a laboratory only having one scale. If your class has multiple scales, we suggest letting the students weigh out the samples.

***Glassware is not required. The use of disposable plastic materials is perfectly acceptable.

***Do not use the Vortex to mix resin solutions as the resin is fragile and the structure will be destroyed.

***The number of drops given are based on glass disposable pipettes. Plastic pipettes can be used, but the number of drops may vary. Check this for your equipment.

***Refrigeration of the resin solutions is preferred, but not required.

***If students run out of time during the course of the experiment, they can finish up the next day. None of these processes are time critical.

Where to buy materials:

The resin, Bromothymol blue, and Bis-Tris we used was purchased at Sigma-Aldrich’s website .

Where to borrow equipment:

If equipment is needed that is not available in lab, the use of the Equipment Loan Program at WSU is recommended. Contact information: (509)335-8528 or e-mail at equipmentloan@wsu.edu.

PREREQUISITE STUDENT SKILLS/KNOWLEDGE

Students should have prior knowledge about such scientific concepts as: Molarity, conversion factors, pH scale, pH indicators, buffers, diffusion, and charged surfaces. Students should also know how to graph and interpret the graphs. They should be able to solve algebraic equations and take effective laboratory notes. They should know lab safety rules and procedures.

LAB SAFETY PROTOCOLS

• Perform laboratory work only when your teacher is present.

• Always read and think about each laboratory assignment before starting.

• Know the location and use of all safety equipment in your laboratory. These should include the safety shower, eye wash, first-aid kit, fire extinguisher, and blanket.

• Wear a laboratory coat or apron and protective glasses or goggles for all laboratory work. Wear shoes (rather than sandals) and tie back loose hair.

• Clear your bench top of all unnecessary materials such as books and clothing before starting your work.

• Check chemical labels twice to make sure you have the correct substance. Pay attention to the hazard classifications shown on the label.

• Some chemical formulas and names differ by only a letter or number. Pay attention to the bottle or jar and to your own test tube or beaker. DO NOT return any excess material to its original container unless authorized by your teacher.

• Never taste laboratory materials. No food, drink, or gum in the laboratory.

• Never look directly down into a test tube; view the contents from the side. Never point the open end of a test tube toward yourself or your neighbor.

• Any laboratory accident, however small, should be reported immediately to your teacher.

• In case of a chemical spill on your skin or clothing rinse the affected area with plenty of water. If the eyes are affected water-washing must begin immediately and continue for 10 to 15 minutes or until professional assistance is obtained.

• Minor skin burns should be placed under cold, running water.

• When discarding used chemicals, carefully follow the instructions provided.

• Return equipment, chemicals, aprons, and protective glasses to their designated locations.

• Before leaving the laboratory, ensure that gas lines and water faucets are shut off.

• If in doubt, ask!

(Adapted from chemvt.edu/rvgs/act/lab/safety_rules.html, 6/29/06)

STUDENT LAB PROCEDURE

Day 1:

Materials:

• Worksheet

• Periodic Table of the Elements

• Scientific calculator

Procedures:

1. Administer pre-test, give students 5 -10 minutes to complete.

2. Review / discuss concepts related to pre-test and prerequisite student skills / knowledge, about 15 minutes.

3. Have the students complete the worksheets and turn them in at the end of class.

4. About 5 minutes before class is over, remind students to dress lab appropriately for the rest of the week.

Pre – Test

Name_______________________________________ Period______ Date: ___________

Directions: Please answer all questions to the best of your ability. In the blanks below, enter the word or number that best completes the statement.

1. If pH is neutral at 7.0, then above 7.0 pH it is _______________ and below 7.0 pH is

it_______________.

2. The molecular weight of NaBr is: ________g /mol

3. On a surface area, like charges __________ and opposite charges__________.

In the space below, please answer the following questions. If you need more space to completely answer the question please use the back of this paper.

4. State three lab rules:

a.

b.

c.

5. Define Diffusion.

6. Describe chromatography.

7. What is a real-life example of ionic exchange chromatography?

8. You have solutions: A, B, C, and D. The pHs are: 3.0, 7.8, 5.2, and 11.7.

Draw a line graph on back of this paper using this information.

Worksheet

Name_______________________________________ Period______ Date: ___________

Find the molar masses of the following compounds and write your answer in the blank next to the question.

1. NaBr _____________ 2. C6H12O6 _____________

3. AgF ____________ 4. Na3PO4 ______________

5. PbSO4 ___________ 6. Ca(OH)2 _____________

pH = - log [ H+ ] [ H+ ] = 10 –pH

Calculate the pH for each [ H+ ] given below and write your answer in the blank next to the question.

7. [ H+ ] = 2.3 x 10-3 , pH = __________

8. [ H+ ] = 7.6 x 10-12 , pH =__________

Determine the [ H+ ] from the pH and write your answer on the blank next to the question

9. pH = 4.5, = ____________

10. pH = 12.7, = ____________

Find the Molarity of the following solutions in the spaces below or on the back of this paper.

11. 0.5 moles of NaCl dissolved to make 0.05 liters of solution.

12. 734 grams of Li2SO4 are dissolved to make 2500 mL of solution.

Worksheet Answer Key

1. 102.9 g/mol

2. 180.0 g/mol

3. 126.9 g/mol

4. 164.0 g/mol

5. 303.3 g/mol

6. 74.1 g/mol

7. pH = 2.64

8. pH = 11.12

9. 0.0000316 M

10. 2.0 x 10-13 M

11. 10 M

12. 2.67 M

Day 2:

Materials:

|100 mL beaker |

|2 – 50 mL Falcon tubes |

|4 – 15 mL Falcon tubes |

|Bromothymol blue 0.04% |

|Distilled (DI) water |

|Graduated cylinder (at least 100 mL) |

|Lab manual |

|Labeling tape |

|Pipette or dropper |

|Stock Resin tube |

|Test tube rack |

|Waste beaker/glass container |

Procedures:

A. Prepare the resin:

1. Invert the stock resin tube five times to mix resin and water.

2. Transfer the resin mixture from the resin stock tube to a 50 mL falcon tube.

3. Rinse out 15 mL tube with DI water to make sure all the resin is in the large Falcon tube.

4. Add DI water to the 50 mL falcon tube to the 40 mL line.

5. Set aside, and complete Part B.

B. Dilute Bromothymol Blue:

1. Put 36 mL of DI water into graduated cylinder.

2. Using a pipette, add 0.04% Bromothymol Blue to the graduated cylinder to reach 40 mL mark.

3. Pour the solution into a 50 mL Falcon tube.

4. Invert the solution five times.

C. Continuation of Resin preparation (from Part A):

1. The resin in the 50 mL Falcon tube should have settled to the bottom of the tube.

2. Pour off the supernatant (liquid portion) slowly, being careful not to pour off the resin.

3. Fill tube with DI water.

4. Replace cap and invert tube five times.

5. Allow to settle for at least 10 minutes.

6. Repeat steps 2-5.

7. Pour off the final supernatant.

8. After wash of resin is complete, add DI water to the 7.5mL mark.

9. Gently shake tube to mix resin and water.

10. Add resin mixture to the 50 mL Falcon with Bromothymol blue (dilute), from Part B.

11. Rinse back and forth between the tubes a few times to get all of the resin.

12. Replace the lid on the 50 mL Falcon containing the dye and resin.

13. Mix by inverting for 10 minutes.

14. Label the Falcon tube, including your group name. Place in the appropriate space.

Day 3:

Materials:

|1 M HCl |

|11 eppendorf tubes |

|600 mL beaker |

|Bromothymol Blue 0.04% |

|Container labeled Bis-Tris |

|DI water |

|Lab manual |

|Labeling tape |

|pH indicator paper |

|Pipette or dropper |

|Stir plate and rods (or glass stir rods) |

Procedures:

A. Create Color Standards of Buffer:

1. Obtain 11 eppendorf tubes.

2. Have one tube labeled for each of the following pHs: 8.0, 7.8, 7.6, 7.4, 7.2, 7.0, 6.8, 6.6, 6.4, 6.2, and 6.0.

3. Add 500mL of DI water to 600 mL beaker.

4. Add contents of container labeled Bis-Tris to the water.

5. Place on stir plate with magnetic stirrer in the solution, or stir with glass rod until dissolved.

6. Add 12 drops of 1M HCl.

7. While administering the HCl, stir the buffer solution.

8. Extract 1 mL of solution and place in eppendorf tube labeled 8.0.

Note: Please use a different pipette for adding the HCl and extracting the sample.

9. Add the following drops of HCl, and extract 1 mL of solution at each pH target:

7.8: Add 6 more drops of 1 M HCl to solution

7.6: Add 14 more drops of 1 M HCl to solution

7.4: Add 13 more drops of 1 M HCl to solution

7.2: Add 16 more drops of 1 M HCl to solution

7.0: Add 25 more drops of 1 M HCl to solution

6.8: Add 25 more drops of 1 M HCl to solution

6.6: Add 34 more drops of 1 M HCl to solution

6.4: Add 33 more drops of 1 M HCl to solution

6.2: Add 34 more drops of 1 M HCl to solution

6.0: Add 27 more drops of 1 M HCl to solution

10. Add three drops of Bromothymol blue 0.04% to each eppendorf tube for a vibrant color standard.

11. Cover each tube and invert twice, making sure to mix the solution well.

12. Place the color standards in your group’s designated area.

13. Using pH paper, check the pH of Buffer solution, and record.

14. Cover the buffer solution with parafilm, or material provided.

15. Place the Buffer solution in your designated areas, double-checking that the beaker is labeled with your group’s name.

Day 4:

Materials:

|0.04% Bromothymol blue |

|4 – 100 mL beakers |

|4 – 50 mL Falcon tubes |

|4 – Eppendorf tubes |

|4 containers with NaCl; 1 each of the following: 20 mM, 100 mM, 250 mM, & 500 mM |

|Buffer solution (from Day 3) |

|Color standards (from Day 3) |

|Graduated cylinder |

|Lab manual |

|Labels |

|Pipette or dropper |

|Resin solution (from Day 2) |

|Stir plate and rods (or glass stir rod) |

|Waste beaker |

Procedures:

A. Separate Resin:

1. Label the 4 – 50mL falcon tubes with each of the [NaCl]: 20 mM, 100 mM, 250 mM, and 500 mM.

2. Invert the tube containing the resin solution (from Day 2) to mix completely.

3. Pour 10mL of the resin solution into each of the 4 labeled tubes. Cap and invert between each pour to keep solution mixed.

4. Set aside resin, and allow to settle.

B. Make NaCl solutions:

1. Label 4 beakers with the following: 20 mM, 100 mM, 250 mM, and 500 mM.

2. Obtain the 4 containers with the following [NaCl]: 20 mM, 100 mM, 250 mM, and 500 mM.

3. Fill each beaker with 100 ml of buffer solution (from Day 3). Use the graduated cylinder, not the lines on the beakers.

4. Add the appropriate container contents to the corresponding beaker, and stir until dissolved.

5. To the 500 mM NaCl buffer solution, add 3 drops of 0.04% Bromothymol blue.

C. Determine starting pHs of Buffer and NaCl solutions (These are the START tubes):

1. Label 4 eppendorf tubes, 1 tube for each [NaCl], and label each with the term “START”.

2. Add 1 mL of each solution to the appropriate eppendorf tube.

3. Add 3 drops of 0.04% Bromothymol blue to each tube.

4. Mix well by inverting.

5. Compare the tubes to the color standards and record pHs.

6. Set the tubes aside.

D. Add NaCl Buffer solution to resin tubes:

1. Pour off supernatant from each resin tube from Part A, placing material in waste beaker.

2. To the corresponding resin tube, fill with the 20 mM NaCl buffer mixture to the 40 mL mark.

3. Invert twice to mix.

4. Repeat steps 1-2 for each of the NaCl concentrations.

5. Let all tubes sit for 15 minutes (or overnight).

6. Repeat steps 1-5.

Day 5:

Materials:

|4 –Eppendorf tubes |

|Color standards (from Day 3) |

|Graph paper |

|Lab manual |

|Labels/Pen |

|Resin and buffer tubes (from Day 4) |

Procedures:

A. Determining ending pH of Buffer solutions (These are the END tubes):

1. With each of the NaCl solutions, compare the color of the resin to the color standards.

2. Record the resin pHs.

3. Label 4 – eppendorf tubes with the different salt concentrations, and label each with the term “END”.

4. Take a 1mL sample of each of the supernatants and place in labeled eppendorf tube.

5. Add 3 drops of 0.04% Bromothymol blue.

6. Cover and invert tubes five times.

7. Compare the color of all supernatant to the color standards, and to the ‘start’ buffer solutions.

8. Record the pH for each.

B. Create a line graph:

1. Graph the pH of the resin on the y-axis, and the [NaCl] of the buffer solution on the

x-axis.

Instructional Strategies:

This teaching module involves components of several different strategies. These include: Direct Instruction, Cooperative Learning, Laboratory, Group Investigation, Data Gathering, and Data Analysis. This module involves teacher-centered instruction, which includes some lecture, and presentation. Because this is a laboratory activity, it is performed in an environment that fosters inquiry through experimentation. Specialized equipment is used to perform the procedures and experiment. The teacher will divide students into groups of two (or more if needed). Groups gather information, assemble their findings, complete the lab questions, and if time allows, have a discussion with the class. Students gather and analyze data during this process. This teaching module allows the students to share knowledge and a positive classroom experience, have a structured activity, and build a positive classroom climate.

Data Collection:

Students collect information in an organized way for use in analysis. The students will follow procedures creating color standards, document drops used, and resulting pH. The students will record all observations throughout the lab. This will be especially significant for the ionic exchange chromatography comparison to the color standards.

Data Analysis:

After having students gather and analyze data, they will be instructed to create dot-line graphs reflecting the relationship between the NaCl concentration and the resin pH. They should be able to connect the data to real-world problems and also improve their critical thinking skills.

Conclusions:

The students should be able to explain what ionic exchange chromatography is, and have a better understanding of the scientific and engineering concepts that were utilized in this teaching module. They should also be able to complete the lab write-up, create the dot-line graphs, and the student evaluation form. Classroom discussion of the lab will allow for a cooperative learning opportunity and true understanding of the concepts to be identified.

EVALUATION PROTOCOLS

The evaluation protocol will vary from teacher to teacher. Possible activities that could be graded that are provided in this module include: completion of the lab, participation in the lab, the pre-test, the worksheet, the lab questions and worksheet in the student lab handbook, the graph activity, and the post- test. An answer key was provided for the Worksheet because there are definite right answers. However, no other answer keys are provided because a variety of answers could be correct. There is a student lab evaluation form included, should you like to use it.

LAB WORKSHEET

Directions: Please fill in the blanks as you progress through this lab.

Buffer stock

Target pH: 8.0 7.8 7.6 7.4 7.2 7.0 6.8 6.6 6.4 6.2 6.0

Drops Added: ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____

START Buffer pH:

20 mM NaCl: __________ 100 mM NaCl: __________

250 mM NaCl: __________ 500 mM NaCl: __________

END Buffer pH:

20 mM NaCl: __________ 100 mM NaCl: __________

250 mM NaCl: __________ 500 mM NaCl: __________

Resin pH:

20 mM NaCl: __________ 100 mM NaCl: __________

250 mM NaCl: __________ 500 mM NaCl: __________

Lab Questions: After completion of this lab, please answer the following questions in the space provided. You may use the back of this sheet if more space is needed.

Describe how resin settled:

Why did some resin settle faster than others?

Using the graph you constructed, predict the pH of the resin exposed to a NaCl concentration of 400 mM? 50 mM?

Post - Test

Name_______________________________________ Period______ Date: ___________

Directions: Please answer the following questions in the space provided as completely as possible. If you need more room, please use the back of this sheet.

1. Define “Hard Water”.

2. Explain how a home water softening system works.

3. Explain the relationship between the ionic exchange lab that you performed and the

recharging of the water softening system through the addition of salt.

4. In the experiment, why did the pH of the resin change when introduced to the NaCl

solution?

5. What do you believe the main purpose of this lab experiment was?

6. What changes would you have made in your procedures?

Student Evaluation Form

Activity________________________________Class:___________________

Your teacher is involved with a project to develop science lessons. Your input will be helpful if you complete this form at the end of your lab. Please, remember that the questions are about the lesson, not the teacher. Your honest response is crucial. Do not put your name on this paper.

Circle only one answer for each question.

4 – Strongly agree 3 – Agree 2 - Disagree 1- Strongly disagree

1. I learned something new about engineering that I didn’t know before.

4 3 2 1

2. I was explained and understood the objectives before we began.

4 3 2 1

3. I was able to follow the steps in the lab.

4 3 2 1

4. I had all of the materials that I needed to complete the lab.

4 3 2 1

5. I like doing science labs more than reading about them.

4 3 2 1

6. I could explain the lab and concept to another student.

4 3 2 1

7. This science experience has made me interested in knowing more about engineering.

4 3 2 1

8. What did you enjoy the most?

REFERENCES

Amersham Biosciences. Ion Exchange Chromatography & Chromatofocusing, Principles

and Methods, Edition AA.

Arkansas State University, Department of Chemistry and Physics. Worksheets – pH,

cas.astate.edu/draganjac/pH.html. Retrieved on 7/11/06.

Bishop, E., Ed. (1972). Indicators. Pergamon Press, Ltd: Oxford.

Brown, T., LeMay, H.E., Bursten, B.E. (1997) Chemistry: The Central Science. (7th Ed.)

Prentice Hall: Upper Saddle River, New Jersey.

Hardin, A.M., Ivory, C.F. (2006). Buffer salt effect on pH in the interior of an anion

exchange resin. Journal of Colloid and Interface Science: DOI 10.1016/j.jcis.2006.055

In press 07-04-2006.

Hefferich, F. (1962). Ion Exchange. McGraw-Hill Book Company: New York, NY.

Ion Exchange Chromatography (IEC), tutorial/iec. Retrieved

on 7/6/06.

Jansen, M.L., Straathof, A.J., Van Der Wielen, L.A.M., et al. Rigorous model for Ion

Exchange Equilibria of Strong and Weak Electrolytes. AIChE Journal, Vol.42, No. 7,

1996.

Milanco Industrial Chemicals. Fundamentals of pH,

training/fundamen.htm. Retrieved on 7/11/06.

Miller, W.E. Ion Exchange Resins as Indicators. City College: New York, 1958.

Molar Mass Practice Worksheet, . Retrieved on 7/11/06.

Staby, A., Jensen, I.H., Mollerup, I. Comparison of chromatographic ion-exchange resins

I. Strong anion-exchange resins. Journal of Chromatography A, 2000.

Staby, A., Jensen, I.H., Mollerup, I. Comparison of chromatographic ion-exchange resins

II. Strong anion-exchange resins. Journal of Chromatography A, 2001.

Stahlberg, J. Retention models for ions in chromatography. Journal of Chromatography

A, 1999.

Student, Class of 2000. Calculating Molarity,

gcurran/molrcalc.htm. Retrieved on 7/11/06.

Water Softening FAQ’s. doineedawatesoftener.htm. Retrieved on

6/30/06.

Wikipedia. Ion exchange resin, .

Retrieved on 7/11/06.

APPENDIX A

Pictures from the lab:

[pic]

Figure 1: Color standards for the module. The range is pH of 8.0-6.0, with increments of 0.2.

[pic]

Figure 2: Starting and ending NaCl/Buffer solutions. This figure shows that the starting and ending pHs are the same with each [NaCl] before and after the buffer is mixed with the resin. The top line has the starting solutions and bottom line contains the ending solutions.

[pic]

Figure 3: The resin mixed with the varying [NaCl]. Notice how the color changes with increasing [NaCl].

[pic]

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