Solutions: Mixtures, Solubility and Concentration Classwork

PSI AP Chemistry: Solutions

Practice Problems

Name _______________________________

Solutions: Mixtures, Solubility and Concentration Classwork

1. A student determined that there were 0.032 grams of oxygen gas dissolved in a

200.0 mL sample of lake water (D = 1.02 g/mL) at a temperature of 15C.

A. How many oxygen atoms would exist in a 500.0 mL sample of this lake water?

B. If hot water were dumped into the lake from a factory, what would be the affect

on the mole fraction of oxygen in the sample? Justify your answer.

C. What would be the molality and molarity of the 500.0 mL lake water solution?

Ignore the presence of solute other than the oxygen gas.

D. Describe what happened to the magnitude of the molality and molarity of the

lake water after the hot water from the factory was added. Ignore the presence

of solute other than the oxygen gas.

2. An organic compound with formula C2H6O was mixed with CCl4 in one beaker and

water in another beaker. Two layers were absorbed when the compound was mixed

with water and one layer when mixed with CCl4.

A. Is the molecule more polar or more non-polar? Justify your answer.

B. Draw a lewis structure for the compound consistent with the observations of the

experiment.

C. Draw the lewis structure of an isomer of this compound that would have been

miscible in water.

D. Propose how this compound could be separated from the CCl4. Be specific as to

the technique AND the expected observations.

3. Agree or disagree with the following statements and then justify your answer:

A. As the temperature of a solution increases, the mole fraction of solute decreases.

B. An addition of 50 mL of distilled water would be required to dilute a 200 mL

0.12 M solution of HCl to a concentration of 0.08 M.

4. An aqueous mixture of ethylene glycol (C2H6O2) and water is 50% water by volume.

Assuming the total volume of the solution is known, what data would be required to

determine the mole fraction of ethylene glycol in the mixture?

5. How many mL of 0.34 M Pb(NO3)2 would need to be added to a 100 mL solution of

0.50 M NaCl to¡­

A. Precipitate out all of the Cl- ions?

B. Create exactly 1 gram of precipitate?



PSI AP Chemistry

Solutions

Solutions: Formations and Properties Classwork

6. A student prepares 100 mL solutions of 0.1 M HCl, 0.1 M HC2H3O2, and 0.1 M CaCl2:

a. Rank the three solutions from highest to lowest electrical conductivity:

b. Rank the three solutions from highest to lowest vapor pressure:

c. Rank the three solutions from highest to lowest freezing point:

7. The vapor pressure of pure benzene at 100 C is 1500 mm Hg. The vapor pressure of

pure hexane at 100 C is 1600 mm Hg.

a. Which pure substance would have the weaker intermolecular forces? Justify

your answer.

b. What would be the vapor pressure of a solution prepared by adding 60

grams of liquid benzene (C6H6) to 20 grams of liquid hexane (C6H14)?

c. What would be the mole fraction of benzene in the vapor phase above the

solution created in letter ¡°b¡±?

8. To 100 grams of water, a student added equi-molar amounts of compounds X, Y, and

Z and observed the freezing points of each. The results are below:

Compound X

Freezing Point: -5.58 C

Compound Y

Freezing Point: - 3.72 C

Compound Z

Freezing Point: -1.86 C

Assuming the freezing point constant for water is 1.86 C/m¡­..

a. Identify each of the following compounds as either KI, C6H12O6, or MgCl2

b. How many grams of compound Y were in the solution?

9. Explain the following observations in terms of particle interactions and chemical

properties:

a. Pure water makes a poor antifreeze and coolant in an automobile engine but

the addition of ethylene glycol to the water in a roughly 50/50 ratio

dramatically elevates the boiling point and lowers the freezing point.

b. Adding large quantities of salt to water will reduce the cooking time of pasta

(cooked in boiling water).

10. A 3.56 gram sample of a non-volatile, non-ionic solute is added to 100.0 mL of water

and the boiling point is measured to be 100.45 C at 1 atm pressure. Assuming the Kb

for water is 0.51 C/m, what is the molar mass of the solute?



PSI AP Chemistry

Solutions

Solutions: Formations and Properties Homework

11. A student needs to prepare 40.0 mL of a 0.25 M NaOH solution.

a. Explain how such a solution could be prepared using solid NaOH, a

balance, a beaker, distilled water, and a volumetric flask.

b. When the NaOH dissolves, the temperature of the solution increases from

18.2 C to 24.5 C. Assuming the specific heat and density of the solution is

approximately that of water, what is the heat of solution of NaOH in

kJ/mol?

c. Draw a pictoral representation of the solution after the NaOH has

dissolved in the water. Make sure to show each kind of species present

and their orientation to each other.

d. How would the pictoral representation be different for the dissolution of

methanol (CH3OH) in water compared to the picture in ¡°c¡±?

e. Based on your answer to ¡°b¡±, which must have had the greater bond

enthalpies ¨C the solvent-solvent interactions or the solute-solvent

interactions? Justify your answer.

f. If the container in which the NaOH and water were mixed was not well

insulated, would this have made the calculated heat of solution higher or

lower than the theoretical value? Justify your answer.

12. A student prepares 0.1 M aqueous solutions of AlCl3, MgCl2, NaCl, and C6H12O6.

a. Which solution would be the strongest electrolyte? Justify your answer.

b. How would the vapor pressures of these solutions compare to the vapor

pressure of pure water? Explain.

c. Assuming the vapor pressure of pure water is 15.0 mm Hg at 16.0 C, what

would be the vapor pressure of a 100 mL solution of 0.1 M C6H12O6?

Assume a density of the solution equal to 0.997 g/mL.

13. Agree or disagree with the following statements and justify your answer.

a. Antifreeze (a mixture of ethylene glycol ¨C C2H6O2 and water) has a higher

vapor pressure and lower boiling point than pure ethylene glycol.

b. A 0.2 M solution of glucose would be expected to have a higher boiling

point than a 0.05 M AlCl3 solution.

c. More energy is required to boil salt water than distilled water

d. When methanol (CH3OH) dissolves in water, covalent bonds within the

water molecules are broken to allow the solvent to form attractions with

the solute.



PSI AP Chemistry

Solutions

14. A non-volatile and non-ionic compound weighing 2.34 grams was added to 100.0

grams of benzene. The sample was cooled and found to freeze at 4.34 C. Given that

the normal freezing point of benzene is 5.5 C and that benzene has a Kf value of 5.12 C/m, what is the molar mass of the compound.



PSI AP Chemistry

Solutions

Answers

1. A student determined that there were 0.032 grams of oxygen gas dissolved in a

200.0 mL sample of lake water (D = 1.02 g/mL) at a temperature of 15C.

A. How many oxygen atoms would exist in a 500.0 mL sample of this lake water?

3.02 x 1021 atoms O

B. If hot water were dumped into the lake from a factory, what would be the affect

on the mole fraction of oxygen in the sample? Justify your answer.

The mole fraction of oxygen would decrease as the gas is less soluble at high

temperatures so the moles of oxygen gas would decrease while the solvent

amount would stay unchanged.

C. What would be the molality and molarity of the 500.0 mL lake water solution?

Ignore the presence of solute other than the oxygen gas.

M = .00500 mol/L

molality = 0.00490 mol/kg solvent

D. Describe what happened to the magnitude of the molality and molarity of the

lake water after the hot water from the factory was added. Ignore the presence

of solute other than the oxygen gas.

The molarity will decrease as the higher temperature increases the volume.

The molality will remain unchanged as neither moles or kg are affected by

temperature.

2. An organic compound with formula C2H6O was mixed with CCl4 in one beaker and

water in another beaker. Two layers were absorbed when the compound was mixed

with water and one layer when mixed with CCl4.

A. Is the molecule more polar or more non-polar? Justify your answer.

The molecule is non-polar as it was miscible in CCl4 (a non-polar compound)

B. Draw a lewis structure for the compound consistent with the observations of the

experiment.

C. Draw the lewis structure of an isomer of this compound that would have been

miscible in water.



PSI AP Chemistry

Solutions

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