Q: According to Raoult's Law, what is the formula for the vapor pressure of a solution containing a nonvolatile solute?

$$P_\text{solution} = X_\text{solvent} P^\ast_\text{solvent}$$

Q: Which of the following is the correct expression for the total vapor pressure of a solution containing two volatile liquids A and B?

$$P_\text{total} = X_A P^\ast_A + X_B P^\ast_B$$

Question 1

Which of the following statements best describes a colligative property?

Accepted Answer

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

Question 2

According to Raoult's Law, what is the formula for the vapor pressure of a solution containing a nonvolatile solute?

Accepted Answer

$$P_	ext{solution} = X_	ext{solvent} P^\ast_	ext{solvent}$$

Question 3

A solution is made by dissolving 10.0 g of a nonvolatile solute in 100.0 g of water. What happens to the vapor pressure of the water compared to pure water?

Accepted Answer

The vapor pressure decreases.

Question 4

Which of the following is NOT a colligative property?

Accepted Answer

Density increase

Question 5

A solution is prepared by mixing 0.861 mol of acetone ($$P^\ast = 0.191$$ bar) and 1.56 mol of methanol ($$P^\ast = 0.360$$ bar) at 25°C. What is the expected vapor pressure of the solution according to Raoult's Law?

Accepted Answer

$$0.251$$ bar

Question 6

If the actual vapor pressure of the acetone-methanol solution in the previous question is measured to be $$0.215$$ bar, what does this indicate about the nature of the solvent-solute interactions?

Accepted Answer

The solution shows negative deviation from Raoult's Law, indicating stronger interactions between acetone and methanol.

Question 7

Which of the following will have the highest boiling point, assuming equal concentrations?

Accepted Answer

A solution of $$0.05\, m$$ NaCl

Question 8

Which equation correctly expresses the boiling point elevation for a solution?

Accepted Answer

$$\Delta T_b = m K_b$$

Question 9

A nonvolatile solute is added to a solvent. What happens to the boiling point and vapor pressure of the solution compared to the pure solvent?

Accepted Answer

Boiling point increases, vapor pressure decreases.

Question 10

A solution is made by dissolving 10 g of glucose (C$$_6H$_{12}O$_6) in 1 L of $$water and another by dissolving 10 g of sucrose (C$$_{12}H$_{22}O$_{11}) in 1 L of $$water. Which solution has the higher vapor pressure?

Accepted Answer

The glucose solution

Question 11

Which of the following best explains why adding a nonvolatile solute to a solvent lowers the vapor pressure of the solvent?

Accepted Answer

The solute particles occupy surface sites, reducing the number of solvent molecules able to escape into the vapor phase.

Question 12

Which of the following is the correct expression for the total vapor pressure of a solution containing two volatile liquids A and B?

Accepted Answer

$$P_	ext{total} = X_A P^\ast_A + X_B P^\ast_B$$

Question 13

Which of the following real-world scenarios is an example of boiling point elevation due to a colligative property?

Accepted Answer

Adding salt to water to cook pasta, causing the water to boil at a higher temperature.

Question 14

If a solution of acetone and methanol has a vapor pressure lower than predicted by Raoult's Law, what can be inferred about the interactions between acetone and methanol molecules?

Accepted Answer

They have stronger interactions than in the pure substances.

Question 15

Which of the following would you expect to have the lowest vapor pressure at the same temperature and concentration?

Accepted Answer

A solution of NaCl in water

Question 16

A solution is prepared by dissolving a nonvolatile solute in a solvent. Which of the following best describes the effect on the freezing point of the solution?

Accepted Answer

The freezing point decreases.

Question 17

Which of the following best describes the relationship between the mole fraction of solvent and the vapor pressure of a solution according to Raoult's Law?

Accepted Answer

As the mole fraction of solvent increases, the vapor pressure of the solution increases.

Question 18

Which of the following is a correct statement about the effect of a nonvolatile solute on the boiling point of a solvent?

Accepted Answer

The boiling point of the solvent increases.

Question 19

A solution is made by mixing 50.0 g of acetone (CH$$_3$$COCH$$_3) $$and 50.0 g of methanol (CH$$_3OH). If $$the mole fraction of acetone is 0.356 and the vapor pressure of pure acetone is 0.191 bar, what is the partial vapor pressure of acetone in the solution?

Accepted Answer

$$0.068$$ bar

Colligative Properties of Solutions: Vapor Pressure Lowering and Boiling Point Elevation

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