Question 1

Which of the following statements best explains why the temperature of a substance does not change during its melting point, even though heat is being added?

Accepted Answer

The added heat is used to break intermolecular forces, not to increase temperature.

Question 2

A solution is prepared by dissolving NaCl in water. Which of the following best describes the process at the molecular level?

Accepted Answer

NaCl dissociates into Na$$^+$$ and Cl$$^-$$ ions, which are solvated by water molecules.

Question 3

Which of the following substances would you expect to have the highest boiling point, assuming similar molar masses?

Accepted Answer

A substance with hydrogen bonding.

Question 4

Which equation correctly represents the heat required to raise the temperature of a substance within a single phase?

Accepted Answer

$$q = m e C_q \Delta T$$

Question 5

A 1.0 mol sample of water is heated from -25 $$^\circC to 125$$ $$^\circC. $$Which of the following steps requires the most energy?

Accepted Answer

Vaporizing the water at 100 $$^\circC.$$

Question 6

Which of the following best describes the effect of adding a nonvolatile solute to a solvent?

Accepted Answer

It decreases the vapor pressure and increases the boiling point.

Question 7

Which of the following equations represents Raoult’s Law for the vapor pressure of a solution?

Accepted Answer

$$P_{solution} = X_{solvent} P^\circ_{solvent}$$

Question 8

A solution is prepared by dissolving 0.1 mol of CaCl$$_2 in 1.0 kg of $$water. What is the van’t Hoff factor, $$i$$, for this solution, assuming complete dissociation?

Accepted Answer

$$i = 3$$

Question 9

Which of the following best explains why the solubility of gases in water decreases as temperature increases?

Accepted Answer

Gas molecules have higher kinetic energy and escape more easily from the solution.

Question 10

Which of the following is true about colligative properties?

Accepted Answer

They depend only on the concentration of solute particles.

Question 11

A solution is prepared by mixing 0.5 mol of ethanol (a volatile liquid) and 0.5 mol of water. If the vapor pressures of pure ethanol and pure water at a given temperature are 44 mmHg and 24 mmHg, respectively, what is the total vapor pressure of the solution, assuming ideal behavior?

Accepted Answer

$$P_{total} = (0.5)(44) + (0.5)(24) = 34$$ mmHg

Question 12

Which of the following best describes a supercritical fluid?

Accepted Answer

A high-pressure, high-temperature fluid that fills its container like a gas but has density like a liquid.

Question 13

Which of the following best explains why oil and water do not mix?

Accepted Answer

The intermolecular forces between oil and water are much weaker than those between water molecules.

Question 14

Which of the following equations correctly expresses the freezing point depression for a solution?

Accepted Answer

$$\Delta T_f = -i K_f m$$

Question 15

A red blood cell is placed in a hypotonic solution. What will happen to the cell?

Accepted Answer

Water will move into the cell, causing it to swell and possibly burst.

Question 16

Which of the following best describes the process of osmosis?

Accepted Answer

Solvent moves from low solute concentration to high solute concentration through a semipermeable membrane.

Question 17

Which of the following is the correct expression for the osmotic pressure of a solution?

Accepted Answer

$$\Pi = i M R T$$

Question 18

A solution is prepared by dissolving 0.2 mol of sucrose (a non-electrolyte) in 1.0 kg of water. If the freezing point depression constant for water is $$K_f = 1.86 \ ^\circ \mathrm{C} \cdot \mathrm{kg} / \mathrm{mol}$$, what is the expected freezing point depression?

Accepted Answer

$$\Delta T_f = -0.372 ^\circ \mathrm{C}$$

Question 19

According to Henry’s Law, which of the following will increase the solubility of a gas in a liquid?

Accepted Answer

Increasing the partial pressure of the gas above the liquid.

Properties of Liquids, Intermolecular Forces, and Phase Changes

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