Chapter 13 Test

Question 1

When 3.00 g KNO3 are dissolved in 50 g glycerol, the freezing point changes from 17.8°C to 13.6°C. What is the freezing point depression constant (Kf ) for glycerol?

Answer 1

3.5 K/m

Question 2

A certain type of sugar dissolves in water, but the solution created does not conduct electricity. Therefore, the sugar does not form ions when dissolved in solution. When 10.0 g of this sugar are dissolved in 25.0 g of water, the freezing point of the solution is −5.0°C. If the freezing point depression constant for water (Kf) is 1.86°C/m, what is the molar mass of the sugar?

Answer 2

150 g/mol

Question 3

Suppose you add 4.25 g of naphthalene, C10H8, to 67.9 g of benzene, C6H6, and they form an ideal solution. The vapor pressure of pure benzene is 0.1252 atm at the temperature of the experiment. What is the vapor pressure of the benzene above the solution?
The molar mass of naphthalene is 128.17 g / mole and the molar mass of benzene is 78.0 g / mol.

Answer 3

0.121 atm

Question 4

Potassium chloride is used in the kitchen as a salt substitute (in place of sodium chloride). Suppose you were planning to make ice cream but discovered too late that you were out of table salt for making the ice bath. If the recipe called for one pound of NaCl, how would it work to use one pound of KCl instead?

Answer 4

Using KCl would give a solution with a slightly higher freezing point.

Question 5

What is the boiling point of a solution that contains 5.0 g of NaCl dissolved in 25 g of water (Kb for water is 0.51)?

Answer 5

103.5°C

Question 6

Sodium chloride has solubility in water at 100.0°C of 39.1 g sodium chloride per 100 g of water. Calculate the boiling point of a saturated solution of sodium chloride in water. At this concentration, ν is 1.85; Kb for water is 0.513°C / m.

Answer 6

106.3°C

Question 7

To determine the molar mass of an unknown protein, 1.00 mg was dissolved in 1.00 mL of water. At 25.0°C the osmotic pressure of this solution was found to be 1.47 × 10^−3 atm. What is the molar mass of this protein?

Answer 7

1.66 × 10^4 g / mole.

Question 8

What is the osmotic pressure of human blood at 37°C if human blood is isotonic to 0.16 M NaCl solution? Remember that NaCl almost completely ionizes in water, so each formula unit of NaCl contributes two particles to the solution.

Answer 8

8.1 atm

Question 9

What should happen when a solution becomes supersaturated with solute?

Answer 9

some of the solute should precipitate

Question 10

For which of the following pairs is the solute (the first species) not very soluble in the solvent (the second species)?

Answer 10

hexane in water

Question 11

For experiments involving freezing point depression or boiling point elevation, concentrations must be expressed in molality (m) units rather than molarity units (M). The reason for this is

Answer 11

molality is temperature independent, while molarity is temperature dependent.

Question 12

When a solvent dissolves a particular solute, the solution gets colder. Which of the following statements is true?

Answer 12

The enthalpy change is positive, so the entropy change must be positive.

Question 13

Which of the following best describes how water molecules interact with cations and anions of ionic compound?

Answer 13

The positive end of the water dipole moment aligns toward the anion and the negative end of the water dipole moment aligns toward the cation

Question 14

2.0 moles of a nonelectrolyte solute are added to 1.0 kg of an unknown solvent. The freezing point is depressed by 7.9 K. Calculate the molal freezing point constant (Kf ) for this solvent.

Answer 14

3.95 K kg / mol

Question 15

Which of the following has the highest osmotic pressure?

Answer 15

0.10 M solution of CaCl2 in water

Question 16

A solution is made by dissolving 33.7 g of MgCl2 and in 0.35 L of H2O. What are the mass of the solvent and the number of moles of the solute, respectively, in the solution? The density of water is 1.00 g / mL.

Answer 16

0.35 kg H2O; 0.354 mol MgCl2

Question 17

The density of a 1.83 M aqueous solution of methanol is 0.976 g / mL. The molar mass of the solute is 32.04 g / mol. What is the molality of the solution?

Answer 17

2.00 mol / kg

Question 18

What mass of potassium nitrate (KNO3 ) should be added to 5.00 × 102 g of H2O in order to make a 0.300 m KNO3 solution? The molar mass of KNO3 is 101.1 g / mol

Answer 18

15.2 g

Question 19

Suppose a bottle of champagne has a partial pressure of 5.0 atm of CO2 above the liquid. Henry’s law constant (KH ) for CO2 in water at 25°C is 3.1 × 10−2 mol / L-atm. If we assume that champagne is essentially water, how much CO2 is dissolved in the liquid?

Answer 19

0.16 M

Question 20

Consider the form of Henry’s Law.

Pgas = kHXgas

The value of the Henry’s Law constant is found to be temperature-dependent and generally increases with increasing temperature. This indicates that

Answer 20

gases become less soluble with increasing temperature

Question 21

Suppose you have a closed container that is partially full of water and above the water is oxygen gas. Which of the following steps would result in increasing the amount of oxygen dissolved in the water?

Answer 21

addition of more oxygen gas

Question 22

When a solute is dissolved in a solvent, the boiling point is raised and the freezing point is lowered. What is the practical significance of this information?

Answer 22

• It can be used to protect car engines from freezing in cold weather.
• It can be used to make ice cream in the summer.
• It can be used to determine the molecular mass of an unknown substance.

Question 23

Which of the following does not affect the boiling point elevation of solution?

Answer 23

molar mass of the solvent

Question 24

Look at the diagram of an extraction.

Which statement best explains why iodine transfers from the water to the hexane?

Answer 24

Both iodine and hexane are relatively nonpolar.

Question 25

Suppose that you have oxygen in solution (of water) at 25°C. If the Henry’s law constant = 4.3 × 103 atm and the partial pressure of oxygen is 0.22 atm, what is the mole fraction of oxygen in the solution?

Answer 25

5.11 × 10^−5