Boiling Point Elevation and Freezing Point Depression (13.3.2)

Question 1

• As solute is added to a solvent, the vapor pressure of the solvent decreases, increasing the boiling point of the solution.

Answer 1

• As solute is added to a solvent, the vapor pressure of the solvent decreases, increasing the boiling point of the solution.

Question 2

• As more solute is added and the vapor pressure drops, the triple point of the solution decreases causing a depression in the freezing point.

Answer 2

• As more solute is added and the vapor pressure drops, the triple point of the solution decreases causing a depression in the freezing point.

Question 3

• Mathematical relationships relating the concentration of solute to the change in freezing or boiling point are ∆Tf = – Kfm and ∆Tb = Kbm.

Answer 3

• Mathematical relationships relating the concentration of solute to the change in freezing or boiling point are ∆Tf = – Kfm and ∆Tb = Kbm.

Question 4

Adding a solute makes a solution more stable by increasing what?

Answer 4

Entropy (A)

Adding a solute makes a solution more stable by increasing entropy, or disorder. Since the solution has a higher degree of disorder than the solvent, it is more stable. Boiling point is raised and freezing point is lowered.

Question 5

How does depressing the vapor pressure affect the boiling point and the freezing point of a solution?

Answer 5

The vapor pressure raises the boiling point and lowers the freezing point. (B)

Question 6

Which of the following is an ideal solution?

Answer 6

all of these (D)

Question 7

A colligative property depends on the…

Answer 7

amount of solute (C)

Question 8

If the vapor pressure of a solution is directly proportional to the mole fraction of solvent present, the solution is said to be what?

Answer 8

ideal (C)

By definition, a solution which has a vapor pressure that is directly proportional to the mole fraction of the solvent present is said to be ideal.

Question 9

A student adds 0.10 mol of sodium chloride to a beaker containing 500 mL of water. The water is brought to a boil and the boiling point measured. The boiling point is elevated about twice as much as the student expected. What happened?

Answer 9

The student forgot that each unit of sodium chloride contributes two particles. (C)

Question 10

How is the phase diagram of a solvent changed when a solute is added?

Answer 10

The vapor-liquid boundary moves down (C)

Question 11

Which of the following can be determined if the boiling-point elevation, the mass of solute and the molality of a given solution are known.

Answer 11

The molecular weight of the solute (D)

Question 12

Raoult’s law states that vapor pressure of a solvent ____ when a non-volatile solute is added.

Answer 12

decreases (B)

Question 13

Colligative properties are properties of a solution that depend on the ________ but not the _________ of the solute particles.

Answer 13

number, identity (C)

Colligative properties are properties of a solution that depend on the number but not the identity of the solute particles.