Q: According to Raoult’s Law, what is the formula for the vapor pressure of a volatile solvent above a solution?

$$P_{\text{solution}} = P$$^{\circ}$$_{\text{solvent}} \cdot \chi_{\text{solvent}}$$

Q: Which equation correctly expresses vapor pressure lowering?

$$\Delta P = P$$^{\circ}$$_{\text{solvent}} - P_{\text{solution}} = P$$^{\circ}$$_{\text{solvent}} \cdot \chi_{\text{solute}}$$

Q: A solution is made by dissolving 2 mol of a nonvolatile solute in 8 mol of solvent. What is the mole fraction of the solute?

$$\chi_{\text{solute}} = \frac{2}{2+8} = 0.2$$

Question 1

Which of the following best describes a colligative property?

Accepted Answer

A property that depends only on the number of solute particles, not their identity.

Question 2

According to Raoult’s Law, what is the formula for the vapor pressure of a volatile solvent above a solution?

Accepted Answer

$$P_{	ext{solution}} = P$$^{\circ}$$_{	ext{solvent}} \cdot \chi_{	ext{solvent}}$$

Question 3

A solution is made by dissolving a nonvolatile, nonelectrolyte solute in water. Which statement is true about the vapor pressure of the solution compared to pure water?

Accepted Answer

The vapor pressure of the solution is lower than that of pure water.

Question 4

If the mole fraction of the solute in a solution is 0.200 and the vapor pressure of the pure solvent is 100.0 torr, what is the vapor pressure of the solution?

Accepted Answer

80.0 torr

Question 5

What is the term for the difference between the vapor pressure of the pure solvent and the vapor pressure of the solvent in solution?

Accepted Answer

Vapor pressure lowering

Question 6

Which equation correctly expresses vapor pressure lowering?

Accepted Answer

$$\Delta P = P$$^{\circ}$$_{	ext{solvent}} - P_{	ext{solution}} = P$$^{\circ}$$_{	ext{solvent}} \cdot \chi_{	ext{solute}}$$

Question 7

Why does the addition of a nonvolatile solute to a solvent lower the solvent’s vapor pressure?

Accepted Answer

Solute particles replace some solvent molecules at the surface, reducing the rate of vaporization.

Question 8

Which of the following statements about freezing point depression is correct?

Accepted Answer

The freezing point of a solution is lower than the freezing point of the pure solvent.

Question 9

What is the formula for freezing point depression?

Accepted Answer

$$\Delta T_f = K_f \cdot m$$

Question 10

A 1.0 m solution of a nonionic solute is prepared using water as the solvent. Another 1.0 m solution is prepared using ethanol as the solvent. Which solution will have the greater increase in boiling point?

Accepted Answer

The solution with water as the solvent

Question 11

Which equation represents boiling point elevation?

Accepted Answer

$$\Delta T_b = K_b \cdot m$$

Question 12

If a nonvolatile solute is added to a solvent, what happens to the boiling point and freezing point of the solution?

Accepted Answer

Boiling point increases, freezing point decreases

Question 13

Which property is NOT a colligative property?

Accepted Answer

Color of the solution

Question 14

A solution is made by dissolving 2 mol of a nonvolatile solute in 8 mol of solvent. What is the mole fraction of the solute?

Accepted Answer

$$\chi_{	ext{solute}} = \frac{2}{2+8} = 0.2$$

Question 15

Which of the following best explains why salt is used to melt ice on roads in winter?

Accepted Answer

Salt lowers the freezing point of water, causing ice to melt at lower temperatures.

Question 16

Which factor determines the magnitude of freezing point depression for a given solvent?

Accepted Answer

The molal concentration of solute particles and the freezing point depression constant ($$K_f)$$

Question 17

A chemist prepares a solution by dissolving a nonvolatile solute in benzene. If the molality of the solution is 2.0 m and $$K_f$$ for benzene is 5.12 $$\degreeC/m$$, what is the expected freezing point depression?

Accepted Answer

$$\Delta T_f = 5.12 	imes 2.0 = 10.24\degreeC$$

Question 18

Which scenario would result in the greatest boiling point elevation for a solution?

Accepted Answer

A solution with the highest molal concentration of solute and a solvent with the largest $$K_b$$ value.

Question 19

In a medical scenario, intravenous solutions are carefully prepared to avoid causing cell damage. Which colligative property is most relevant to preventing hemolysis (bursting of red blood cells)?

Accepted Answer

Osmotic pressure

Question 20

A student prepares a solution by dissolving a nonvolatile solute in diethyl ether. If the normal boiling point of diethyl ether is 34.6$$\degreeC $$and $$K_b is 2.02$\degreeC/m$$, what will be the boiling point of a 3.0 m solution?

Accepted Answer

Boiling point = $$34.6 + (2.02 	imes 3.0) = 40.66\degreeC$$

Colligative Properties and Phase Changes in Solutions

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