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Solutions

PreAP 2011

This packet needs a TON of work!!! Please fix it!!!

Add volatile and nonvolatile. Remove notes pages?

Add steps for making a solution (volumetric flask, etc.)

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EVERY DAY you need to bring your calculator!!

| |In Class |Homework (you write in the assignment for the |

| | |night) |

|Wed/Thurs |Molarity and Dilutions | |

|Tues/Wed | | |

|Thurs/Fri | | |

|Mon/Tues | | |

|Wed/Thurs | | |

|Fri/Mon | | |

|Tues/Wed | | |

*Fill in the schedule and assignments every day in class as we progress. Be flexible!

Read the notes and summarize the following properties of water. Define. Explain. Draw pictures.

*High specific heat; ice floats; surface tension; water as a solvent; capillary action

Properties of water Practice

1) What is strange about the fact that ice floats compared to other substances?

2) What is surface tension?

3) Briefly describe how water dissolves NaCl.

4) Describe why water can NOT dissolve nonpolar substances, like oil.

5) What property of water do plants take advantage of to get water from its roots to its stems?

6) Why does water form drops that are round?

7) If the properties of water were to change so that the solid form was denser than the liquid form, organisms living in a cold pond environment would be less likely to survive because water would no longer —

a. dissolve enough oxygen from the air

b. produce solutions containing vital nutrients

c. remain neutral, instead becoming highly acidic

d. produce a floating insulating layer of ice 

8) When water and oil are shaken together, they might appear mixed for a time, but soon separate into layers. Oil and water are not soluble in each other, so they are said to be immiscible. Which of the following factors is the reason oil and water are immiscible?

a. The temperature it too low

b. They were shaken but not consistently stirred

c. No catalyst was added

d. Oil is nonpolar and water is polar. 

9) Table salt, the ionic compound sodium chloride, dissolved in water. Water’s ability to dissolve sodium chloride is related to the

a. Number of protons present in each atom’s nucleus.

b. Number of electrons present in a water molecule.

c. Polarity and structure of water.

d. Amount of solution you are trying to make.

Water: The Universal Solvent (Practice)

1) Water is often called the _____________________ solvent because many substances can dissolve in it.

2) Draw a sketch of a water molecule in the box:

a. Label the oxygen and hydrogen atoms

b. Label which atoms carry a partial positive charge

and which carry a partial negative charge.

3) Why is water considered a polar molecule?

4) Complete the Venn Diagram: O-H bonds within O-H bonds between

1 water molecule 2 water molecules

5) How does the structure of water cause it to form hydrogen bonds?

6) Which do you think is stronger (harder to break): the covalent bond in a water molecule or a hydrogen bond between 2 water molecules? Explain.

7) _____________________ bonding makes water molecules ‘stick’ together. When water sticks to other water molecules it is called, ______________________. When water molecules stick to other molecules it is called ____________________.

8) What property of water might explain why it has such a high boiling point compared to other molecules of similar mass (like O2, which is a gas at room temperature)? Explain.

9) What are the three states that water exists on Earth as? _________________, _________________, _________________

List any other substances you can think of that exist in different states on earth. How are they different than water?

a)

b)

Based on your reading, try these TAKS questions…

10) Fish survive through severe winters because of the property of water that allows water to —

a. form chemical bonds as it freezes, raising the water temperature below the ice

b. increase in density while it freezes, dissolving more oxygen from the air

c. expand when it freezes, creating a floating and insulating layer of ice

d. precipitate vital nutrients when it freezes, increasing the food supply

11) What characteristic of water remains the same no matter what is dissolved in it?

a. The ratio of hydrogen to oxygen c. The ability to refract light

b. The hydroxide ion concentration d. The freezing temperature

12) Which property of water is the main reason it is such an effective solvent?

a. Its high specific heat b. Polarity c. The ease with which it changes state d. Hydrogen bonding

Solutions and Molarity

Example #1: Calculate the molarity, M, of a solution prepared by dissolving 12.0 grams of potassium permanganate, KMnO4, in enough water to make 750.0 ml of solution.

Example #2: Calculate the moles of NaCl needed to prepare 175 ml of 0.500 M saline (salt) solution.

Example #3: Calculate the number of liters of solvent needed to prepare a 2.5 M sodium hydroxide solution containing 31.52 moles of NaOH.

Molarity Assignments

1. Identify the solute and solvent in the following solutions:

a) 10.0 g of sugar & 40.0 g of water solute: ____________solvent: ___________

b) 50 g of water & 5.0 g of NaCl solute: ____________solvent: ___________

c) 18.0 L of nitrogen & 12.0 L of oxygen solute: ____________solvent: ___________

d) 200 g of alcohol & 200 g of water solute: ____________solvent: ___________

(density alcohol = 0.94 g/mL density water = 1.00 g/mL)

2. Calculate the molarity, M, of a solution prepared by dissolving 20.0 g of sodium chloride in 1.0 L of water. (A: 0.34 M)

3. Calculate the molarity, M, of a solution prepared by dissolving 3.50 g of calcium hydroxide in enough water to make 100.0 mL of solution. (A: 0.472 M)

4. What is the molarity if 0.25 g of lead(II) nitrate is used to make 500.0 mL of solution? (A: 0.0015 M)

5. Calculate the volume of water (in liters) needed to prepare a 12.5 M solution containing 31.52 moles of copper (I) hydroxide. (A: 2.52 L)

6. What would be the volume, in liters, of a 2.00 M solution made with 6.00 moles of lithium fluoride? (A: 3.00L)

7. How many moles of strontium nitrate would be used in the preparation of 2.50 L of a 3.5 M solution? (A: 8.8 moles)

8. How many moles of calcium chloride would be used in making 300.0 mL of a 5.0M solution? (A: 1.5 moles)

Dilutions

M1V1  =  M2V2

M1 = Molarity before dilution; V1 = Volume before dilution

M2 = Molarity after dilution; V2 = TOTAL Volume after dilution (initial volume PLUS the added solvent)

***Volumes do not need to be converted to liters as long as the units are the same on each side.

Example #1: 50 ml of a solution are diluted to a volume of 100 ml. The concentration of the diluted solution is 2 M. What was the concentration of the original solution?

Example #2: You have 53 ml of a 1.5 M solution of NaCl, but 0.80 M solution is needed. How many ml should you add?

Example #3: How much water needs to be added to dilute a 10.0 M stock solution of NaCl to make 200.0 mL of a 0.50 M NaCl solution?

Dilutions Practice Problems

Directions: Acids and bases are usually purchased in concentrated form. Rarely, however, is the acid or base used in its concentrated form – it must be diluted to the exact concentration needed. Use the table below to answer the following questions. As always, show all work to earn full credit.

|Concentrated Stock Solution |Molarity of Concentrate (M) |

|NH4OH |14.5 |

|Formic Acid (HCOOH) |23.6 |

|HCl |12.1 |

|HF |28.9 |

|HNO3 |15.9 |

|HClO4 |9.1 |

|H3PO4 |14.8 |

|KOH |11.7 |

|NaOH |19.4 |

|H2SO4 |18.0 |

1. What volume of concentrated hydrochloric acid is needed to make 3.00 L of a 1.00 M solution? (A: 0.248 L)

2. What volume of concentrated ammonium hydroxide is needed to make 250 mL of a 500.0 mM solution? (A:8.6 mL)

3. To perform an experiment, you need 0.300 L of 6.0 M nitric acid. You go to the acid cabinet and discover that you have 100.0 mL of concentrate. Will you have enough acid to complete the experiment? Explain why. (A: 113 mL, No)

4. 30.0 L of an unknown, concentrated acid with water to produce 222 L of solution. The molarity of the resulting solution is determined to be 2.0 M by titration (we’ll learn how to titrate soon!). What type of acid is it? (A: phosphoric acid)

5. Make 100.0 mL of a solution that is 5 mM MgCl2, 75 mM CaCl2 and 125 mM KCl from 1 M stocks of each of these chemicals. How much of each stock solution is needed, and how much water would be added? (A: 0.5 mL MgCl2, 7.5 mL CaCl2, 12.5 mL KCl, 79.5 mL H2O)

SOLUBILITY

Solubility Practice

1. Based on the solubility chart to the right, decide whether

each of the samples below is U: unsaturated, S: saturated,

SS: supersaturated, or N: not enough information is given.

a) 50 g KCl in 100 g of water at 90°C. ____

b) 50 g KCl in 100 g of water at 60°C. ____

c) 50 g KNO3 in 100 g of water at 60°C. ____

d) 50 g KNO3 in 50 g of water at 60°C. ____

e) 65 g KNO3 in 50 g of water at 70°C. ____

f) 25 g KNO3 in 100 g of water. ____

g) 25 g NaCl in 100 g of water. ____

h) 40 g of KCl in 100 g of water at 20°C. ____

i) 50 g of KCl in 100 g of water at 80°C. ____

j) 50 g KNO3 in 25 g of water at 60°C. ____

k) 15 g KNO3 in 50 g of water at 70°C. ____

2. Based on brief solubility rules to the right, which of the following

salts would have the greatest solubility in water at 25°C?

 A. CaCO3 B. FeS C. HgCl2 D. KClO4

3. A 0.2 g crystal of gypsum dissolves very slowly in 100 mL of water while

the water is stirred. How could the gypsum be made to dissolve faster?

4. A student is trying to dissolve a powder in water but it will not dissolve.

Suggest a different solvent that might dissolve the powder.

5. Explain why you cannot wash oil and grease off of your hands with water alone.

6. Over time an open soft drink will lose carbonation (dissolved CO2). Which of these

allows the CO2 to remain in solution the longest? 

A. Reduced air pressure C. Increased air currents

B. Exposure to direct sunlight D. Cooler temperatures

7. As a scuba diver goes deeper underwater, the diver must be aware that the increased pressure affects the human body by increasing the

A. body’s temperature

B. amount of dissolved gases in the body

C. amount of suspended solids in the body

D. concentration

Properties of Solutions Practice Problems

1. How many particles with the following substances become in solution?

|Substance |# of particles |Substance |# of particles |

|Barium chloride, BaCl2 | |Iron (III) nitrate, Fe(NO3)3 | |

|Sodium bromide, NaBr | |Sucrose, C12H22O11 | |

|Aluminum sulfate, Al2(SO4)3 | |Dinitrogen pentoxide, N2O5 | |

|Calcium hydroxide, Ca(OH)2 | |Carbon dioxide, CO2 | |

2. Rank the following solutions in order from lowest boiling point (BP) to highest BP:

(Hint: the higher the # of particles, the higher the BP)

___ 3.0 M Ca(NO3)2 ___4.0 M Ca(NO3)2 ___ 1.0 M KNO3 ___ 2.0 M KNO3

3. Which of these correctly shows how MgCl2 dissociates when dissolved in water?

a. MgCl2 (aq) → Mg+ (aq) + 2Cl- (aq)

b. MgCl2 (aq) → Mg+ (aq) + Cl- (aq)

c. MgCl2 (aq) → Mg+2 (aq) + 2Cl- (aq)

4. How strong of electrolytes are ionic compounds? _____________

How strong of electrolytes are covalent compounds? ___________

How strong of electrolytes are organic compounds? ____________

5. Circle the correct type for the following solutions:

a) NaCl (aq): electrolyte or nonelectrolyte

b) CCl4 (l): electrolyte or nonelectrolyte

c) KNO3 (aq): electrolyte or nonelectrolyte

d) O2 (g): electrolyte or nonelectrolyte

6. As the number of nonvolatile solute particles increases,

a. the solubility of the solute decreases. b. the boiling point of a solution increases.

c. the osmotic pressure of a solution decreases. d. the freezing point of a solution increases.

7. What is one reason that dehydrated patients are given intravenous (IV) solutions of pure water with a small amount of dissolved salt, rather than just pure water?

a. To help prevent cells from shriveling because of the pressure caused by osmosis

b. So that the pressure caused by osmosis will cause a net movement of salt into cells

c. So that dissolved substances will be transported across cell membranes and out of cells

d. To help keep the concentrations of dissolved substances inside and outside the cells equa

8. Which would most likely cause the liquid in Tube A to rise?

a. Starch concentrations being equal on each side of the membrane

b. Water passing from a region of lower starch concentration

to one of higher starch concentration

c. Water and starch volumes being the same

d. Solute in the tubes changing from a higher temperature

to a lower temperature

Acids and Bases – Just the Basics!

*define acids and bases and distinguish between Arrhenius and Bronsted-Lowry definitions and predict products in acid base reactions that form water;

*define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution;

*distinguish between degrees of dissociation for strong and weak acids and bases.

Strong vs. Weak AND Concentrated vs. Dilute

In this activity, you will depict concentrated and dilute solutions of two imaginary acids – one strong (HSt) and the other weak (HWe).

In referring to an acidic solution, as you recall, strong indicates that all (or nearly all) acid molecules have reacted with the water to produce hydronium ions (_________) and anions. By contrast, concentrated indicates that there are a very large number of particles – molecules or ions – dissolved in a particular volume of solution.

Let’s determine the models we’ll use to represent each of the following:

|Unionized Strong Acid |Ionized Strong Acid |

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|Unionized Weak Acid |Ionized Weak Acid |

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Four boxes are drawn on the back of your worksheet. Each box represents 1.0 L of solution. Use H+ to represent hydrogen ions. Each H+ symbol will represent 0.1 mol of dissolved hydrogen ions. Do not draw the solution’s water molecules.

Inside each box, draw between 2 and 20 acid molecules, or the appropriate number of hydrogen ions and anions, to illustrate the following conditions:

• In the first box, depict a concentrated strong acid (HSt) solution.

• In the second box, depict a dilute strong acid (HSt) solution.

• In the third box, depict a concentrated weak acid (HWe) solution.

• In the fourth box, depict a dilute weak acid (HWe) solution.

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| | |

Use your depictions to answer the following questions:

1. Explain the difference between each pair of words used to describe the solutions of an acid or base:

a. weak, dilute

b. strong, concentrated

2. How would the pH values for the four solutions that you depicted compare to one another?

3. Why is it easier to use a single symbol to represent 0.1 mol of particles, rather than trying to draw every particle in 0.1 mol of ions?

4. How might your model drawings mislead a viewer about what is actually present in each solution?

Equations:

pH = -log[H+], pOH = -log[OH_]

pH + pOH = 14

Calculations Practice

|0.150 M LiOH |[H+] |Acidic or Basic? (circle) |

|6x106 M HI |[OH-] |Acidic or Basic? (circle) |

|0.003 M Be(OH)2 |pH |Acidic or Basic? (circle) |

|(assume 2% dissociation) | | |

|8.0 M H2SO3 |[H+] |Acidic or Basic? (circle) |

|(assume 8% dissociation) | | |

|1.0 M HF |pH, pOH |Acidic or Basic? (circle) |

|(assume 4% dissociation) | | |

Plot the above solutions on the pH scale below.

Circle the strong acids and bases. Do strength and pH always go together?

0 7 14

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**List strong acids and bases here:

Why won’t some things dissolve in water?

“Like dissolves like”

The solute and the solvent have to be similar to each other

_________________ molecules have unevenly shared electrons in their bonds. They have _____ and _____ areas that are attracted to each other. __________________ is an example of a polar molecule.

______________________ molecules have evenly shared electrons and there are no partial charges on the molecule. They are not attracted to each other or to polar molecules. _________ is an example of a nonpolar molecule.

Polar solvents, such as water, will dissolve polar and ionic solutes like salt and sugar. Nonpolar solvents, such as oils, will dissolve other nonpolar solutes, like wax.

_____________________is the process when solute molecules become surrounded by solvent molecules.

___________________________ is a measure of how much solute can dissolve in a certain solvent.

Substances that dissolve easily in a certain solvent are called ___________________________.

Example:

Substances that do not dissolve in a certain solvent are called ___________________________.

Example:

Two liquids that dissolve in each other are called __________________________________.

Example:

Two liquids that will not dissolve in each other are called __________________________________.

Example:

Factors that increase the rate of dissolving a solid in a liquid

1. ___________________________ - Increase of surface area increases rate of dissolving. Increase surface area by breaking/grinding solid.

2. ______________________ – Shaking/stirring a solution will increase the rate of dissolving.

3. ___________________- Increases the temperature and usually increases the rate of dissolving.

Factors that increase the rate of dissolving for a gas in a liquid

1. _____________________- INCREASE IN TEMPERATURE USUALLY DECREASES THE RATE OF DISSOLVING

2. _____________________- Increase in pressure increases the rate of dissolving.

***Pressure has little/no effect on the dissolving rate of a solid in a liquid***

________________________ – the solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid.

Example: _______________________.

Brief Solubility Rules

1. All sodium, potassium, and ammonium salts are soluble.

2. Silver, lead, and mercury salts are insoluble.

3. Carbonates, sulfides, and hydroxides are insoluble.

4. Sulfates are soluble except calcium sulfate or barium sulfate.

Osmotic Pressure- When the concentrations of solutes are different on either side of a _____________________ membrane, water is pressured to flow across the membrane to ____________________ the concentrations.

|If these two beakers were connected by a tube |[pic] |

|that contained a semi-permeable membrane, the | |

|water molecules would flow from the side where| |

|[_________] is higher to the side where | |

|[_________] is lower. | |

|This flow of water, from higher [H2O] to lower|[pic] |

|[H2O], results in a change in ______________ | |

|of the two sides. The side that also has the | |

|solute has a larger volume. | |

Freezing Point Depression (_______) - When a solute is present, the orderly pattern that the pure solvent normally takes when freezing is disrupted. _________ kinetic energy must be lost from the solution for it to solidify (freeze). This __________ the freezing point of the solution.

Boiling Point Elevation (_____)– the boiling point of a solution is _______________________ than the boiling point of the pure solvent. Solvent molecules are _____________________ to the solute particles, and that attraction requires energy to break.

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How do you tell how many particles there are?

• _________________ (_____________) do NOT ionize so they stay as one particle. Example C6H12O6

• ____________ compounds will break into their ions:

NaCl ( Na+ + Cl- ___ particles

Na2SO4 ( 2Na+ + SO4-2 ___ particles

(NH4)3PO4 ( 3NH4+1 + PO4-3 ___ particles

Notice the polyatomic ions in solutes

did not dissociate further.

Colligative properties of solutions are properties that depend upon the __________________ of solute molecules or ions, but NOT upon the ________________________________ of the solute.

Colligative properties include freezing point ____________________, boiling point _________________, _____________________ pressure, and _____________________ pressure.

Colligative Properties of Solutions

Some solutions conduct electricity, some don’t

Electrolytes – compounds that conduct an electric current in an aqueous solution OR in the molten state. An electrolyte solution contains charged particles (___________), which can move. Any _________ (ionic compound) dissolved in water is an electrolyte: NaCl, KI, etc.

Types of Electrolytes

_________________________ — a large portion of the solute exists as ions

_________________________ — only a small portion of the solute exists as ions

_________________________ — compounds that do NOT conduct electricity

➢ distilled water

➢ gases

➢ molecular compounds (2 nonmetals)

➢ organic compounds – alcohols, sugars, etc.

➢ Carbon based compounds

How To Make a Solution

1. Measure the mass of solute needed

2. Place in a volumetric flask and fill partially with water

3. When the solute has dissolved, fill to the line on the volumetric flask

“We are drowning in information, while starving for wisdom. The world henceforth will be run by synthesizers, people able to put together the right information at the right time, think critically about it, and make important choices wisely.”

-E.O. Wilson

Vapor Pressure - The pressure of a gas over a solution.

When discussing aqueous solutions with nonvolatile solutes, the gas is water vapor.

As the concentration of the solute ____________, the vapor pressure of the solvent _______________. This is because:

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