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

$P_\text{solution} = P_\text{solvent}^\circ X_\text{solvent}$

Question 1

Which of the following best explains why the vapor pressure of a solution containing a nonvolatile solute is lower than that of the pure solvent, as depicted in the first image?

Accepted Answer

The nonvolatile solute occupies surface sites, reducing the number of solvent molecules at the surface and thus fewer can vaporize.

Question 2

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

Accepted Answer

$P_	ext{solution} = P_	ext{solvent}^\circ X_	ext{solvent}$

Question 3

A solution is made by dissolving 24.5 g of glycerin ($C_3H_8O_3$) in 135 mL of water at 30.0 °C. The vapor pressure of pure water at this temperature is 31.8 torr. What is the vapor pressure of the solution? (Molar mass of glycerin = 92.09 g/mol, density of water = 1.00 g/mL)

Accepted Answer

30.7 torr

Question 4

Which scenario would result in a positive deviation from Raoult’s Law, as shown in the third graph image?

Accepted Answer

Weak solute-solvent interactions

Question 5

What is the effect on the boiling point of a solvent when a nonvolatile solute is added, and what is the equation for the boiling point elevation?

Accepted Answer

The boiling point increases; $\Delta T_b = k_b m$

Question 6

A solution is prepared by dissolving 9.66 g of glucose ($C_6H_{12}O_6$) in 29.90 g of water. What is the freezing point of the solution? ($k_f$ for water = 1.86 °C/m, molar mass of glucose = 180.2 g/mol)

Accepted Answer

$-3.33\ ^\circ\mathrm{C}$

Question 7

Which of the following best describes the process of osmosis as shown in the U-tube diagram?

Accepted Answer

Solvent molecules move through the semipermeable membrane toward the solution with higher solute concentration.

Question 8

What is the equation for osmotic pressure ($\pi$) of a dilute solution?

Accepted Answer

$\pi = MRT$

Question 9

A solution containing 27.55 mg of an unknown protein in 25.0 mL solution has an osmotic pressure of 3.22 torr at 25 °C. What is the molar mass of the protein? ($R = 0.08206\ \mathrm{L\cdot atm/(mol\cdot K)}$, $T = 298.15\ \mathrm{K}$, $1\ \mathrm{atm} = 760\ \mathrm{torr}$)

Accepted Answer

6360 g/mol

Question 10

Which of the following statements about the van’t Hoff factor ($i$) is correct?

Accepted Answer

$i$ is the ratio of the number of moles of particles in solution after dissociation to the number of moles of formula units initially dissolved.

Question 11

What is the expected van’t Hoff factor ($i$) for a solution of $CaCl_2$ assuming complete dissociation?

Accepted Answer

3

Question 12

Which of the following best explains why the experimentally determined van’t Hoff factor ($i$) for an electrolyte is often less than the theoretical value at higher concentrations?

Accepted Answer

Ion pairing reduces the number of free particles in solution.

Question 13

A solution is made by dissolving 29.99 g of $CuCl_2$ in 455.0 g water. Assuming complete dissociation, what is the freezing point of the solution? ($k_f$ for water = 1.86 °C/m, molar mass of $CuCl_2$ = 134.5 g/mol)

Accepted Answer

$-2.73\ ^\circ\mathrm{C}$

Question 14

Which real-world application relies on freezing point depression to function effectively?

Accepted Answer

Adding ethylene glycol (antifreeze) to a car radiator

Question 15

Why is molality ($m$) used instead of molarity ($M$) in calculations of colligative properties?

Accepted Answer

Molality is temperature independent, while molarity changes with temperature.

Question 16

Which of the following intravenous solutions would be safest to administer to a patient, based on osmotic pressure considerations?

Accepted Answer

A solution isotonic with blood plasma

Question 17

A red blood cell is placed in a hypotonic solution. What is the most likely outcome?

Accepted Answer

The cell will swell and possibly burst due to water influx.

Question 18

Which equation correctly relates the freezing point depression to the van’t Hoff factor for an electrolyte solution?

Accepted Answer

$\Delta T_f = i k_f m$

Chapter 14 lecture 3

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