Q: A solution is prepared by dissolving 0.5 mol of NaCl in 1.0 kg of water. What is the molality of the solution?

$$m = \frac{0.5}{1.0} = 0.5~\text{mol/kg}$$

Q: A solution is made by mixing 0.2 mol of KCl with 0.8 mol of water. What is the mole fraction of KCl in the solution?

$$X_{\text{KCl}} = \frac{0.2}{0.2 + 0.8} = 0.2$$

Q: Calculate the freezing point depression for a solution made by dissolving 1.0 mol of NaCl in 1.0 kg of water. ($$K_f$$ for water = $$1.86~^\circ\text{C}/m$$, assume $$i = 1.9)$$

$$\Delta T_f = i \cdot m \cdot K_f = 1.9 \times 1.0 \times 1.86 = 3.53~^\circ\text{C}$$

Q: Which equation correctly expresses Raoult’s Law for the vapor pressure of a solvent in a solution?

$$P_{\text{solvent}} = \chi_{\text{solvent}} \cdot P^\circ_{\text{solvent}}$$

Q: If the vapor pressure of pure water at 55$$^\circC is 118.1 $$torr, what is the vapor pressure of water above a solution containing 0.102 mol Ca(NO$$_3$$)$$_2$$ and 0.927 mol H$$_2O$$? (Assume complete dissociation and use $$i = 3)$$

$$P = 0.75 \times 118.1 = 88.6~\text{torr}$$

Question 1

Which of the following best explains why oil does not dissolve in water?

Accepted Answer

Oil is nonpolar and water is polar, so their intermolecular forces are not compatible.

Question 2

A solution is prepared by dissolving 0.5 mol of NaCl in 1.0 kg of water. What is the molality of the solution?

Accepted Answer

$$m = \frac{0.5}{1.0} = 0.5~	ext{mol/kg}$$

Question 3

Which intermolecular force is primarily responsible for the high boiling point of water?

Accepted Answer

Hydrogen bonding

Question 4

A solution is made by mixing 0.2 mol of KCl with 0.8 mol of water. What is the mole fraction of KCl in the solution?

Accepted Answer

$$X_{	ext{KCl}} = \frac{0.2}{0.2 + 0.8} = 0.2$$

Question 5

Which of the following statements about colligative properties is correct?

Accepted Answer

They depend only on the number of solute particles, not their identity.

Question 6

Calculate the freezing point depression for a solution made by dissolving 1.0 mol of NaCl in 1.0 kg of water. ($$K_f$$ for water = $$1.86~^\circ	ext{C}/m$$, assume $$i = 1.9)$$

Accepted Answer

$$\Delta T_f = i \cdot m \cdot K_f = 1.9 	imes 1.0 	imes 1.86 = 3.53~^\circ	ext{C}$$

Question 7

Which of the following best describes the process of osmosis?

Accepted Answer

The movement of solvent molecules through a semipermeable membrane from low to high solute concentration.

Question 8

A solution is prepared by dissolving 0.1 mol of MgCl$$_2 in 1.0 kg of $$water. What is the expected van’t Hoff factor ($$i) $$for this solution?

Accepted Answer

$$i = 3$$

Question 9

Which equation correctly expresses Raoult’s Law for the vapor pressure of a solvent in a solution?

Accepted Answer

$$P_{	ext{solvent}} = \chi_{	ext{solvent}} \cdot P^\circ_{	ext{solvent}}$$

Question 10

A 0.5 M solution of glucose (a nonelectrolyte) and a 0.5 M solution of NaCl are prepared. Which solution will have the higher osmotic pressure at the same temperature?

Accepted Answer

The NaCl solution, because it produces more particles in solution.

Question 11

If the vapor pressure of pure water at 55$$^\circC is 118.1 $$torr, what is the vapor pressure of water above a solution containing 0.102 mol Ca(NO$$_3$$)$$_2$$ and 0.927 mol H$$_2O$$? (Assume complete dissociation and use $$i = 3)$$

Accepted Answer

$$P = 0.75 	imes 118.1 = 88.6~	ext{torr}$$

Question 12

Which of the following will increase the solubility of a gas in water?

Accepted Answer

Increasing the partial pressure of the gas above the solution.

Question 13

A solution is described as supersaturated. Which of the following best describes this solution?

Accepted Answer

It contains more solute than can normally dissolve at that temperature.

Question 14

Which of the following best explains why the measured van’t Hoff factor for NaCl is less than the expected value?

Accepted Answer

Ion pairing reduces the number of free ions in solution.

Question 15

Which of the following is the correct formula for calculating osmotic pressure ($$\Pi) of a $$solution?

Accepted Answer

$$\Pi = MRT$$

Question 16

A solution is made by dissolving 2.0 mol of FeCl$$_3 in 1.0 kg of $$water. Using the measured van’t Hoff factor ($$i = 3.4$$), what is the total number of moles of particles in solution?

Accepted Answer

$$2.0 	imes 3.4 = 6.8~	ext{mol particles}$$

Question 17

Which of the following pairs of substances will form a solution due to similar intermolecular forces?

Accepted Answer

Ethanol (C$$_2H$_5OH) $$and water (H$$_2O)$$

Question 18

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

Accepted Answer

It lowers the vapor pressure of the solvent.

Question 19

A solution is prepared by dissolving 1.0 mol of glucose (a nonelectrolyte) in 1.0 kg of ethanol. If $$K_f$$ for ethanol is $$1.99~^\circ	ext{C}/m$$, what is the freezing point depression?

Accepted Answer

$$\Delta T_f = 1.0 	imes 1.99 = 1.99~^\circ	ext{C}$$

Question 20

According to Henry’s Law, what is the solubility of O$$_2 in $$water at 25$$^\circC if $$the partial pressure of O$$_2 is 2.0 $$atm? ($$k_H = 1.3 	imes 10$$^{-3}$$~	ext{M/atm})$$

Accepted Answer

$$S_{	ext{O}_2$$} = k_H \cdot $$P_{	ext{O}_2$$} = 1.3 	imes $$10^{-3}$$ 	imes 2.0 = 2.6 	imes $$10^{-3}$$~	ext{M}$$

Solutions and Colligative Properties: Structure, Concentration, and Effects

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