Q: If a solute is only 80% dissociated in water, how would you calculate the van’t Hoff factor ($$i) $$for a solute that would otherwise produce 3 ions per formula unit?

$$i = 1 + 0.8 \times (3 - 1) = 2.6$$

Question 1

Which of the following statements best describes a colligative property?

Accepted Answer

It depends only on the number of solute particles in a solution, not their identity.

Question 2

A solution is prepared by dissolving 31 g of NaCl (molar mass = 58.44 g/mol) in 559 g of water. Assuming complete ionization, what is the boiling point of the solution? ($$K_b$$ for water = $$0.52\ ^\circ\mathrm{C}/m)$$

Accepted Answer

$$100.97\ ^\circ\mathrm{C}$$

Question 3

Which equation correctly expresses the freezing point depression for a solution?

Accepted Answer

$$\Delta T_f = i K_f m$$

Question 4

A nonionizing solute is dissolved in water, lowering the freezing point to $$-7.44\ ^\circ\mathrm{C}. $$What is the molality of the solution? ($$K_f$$ for water = $$1.86\ ^\circ\mathrm{C}/m)$$

Accepted Answer

$$4.00\ m$$

Question 5

Which of the following would produce the greatest freezing point depression when dissolved in 1.0 kg of water, assuming complete dissociation?

Accepted Answer

1.0 mol of $$\mathrm{$$CaCl_2$$}$$

Question 6

A solution is made by dissolving 388 g of ethylene glycol ($$\mathrm{C_2H_6O_2}$$, molar mass = 62.07 g/mol) in 409 g of water. What is the freezing point of the solution? ($$K_f$$ for water = $$1.86\ ^\circ\mathrm{C}/m)$$

Accepted Answer

$$-17.6\ ^\circ\mathrm{C}$$

Question 7

If 4.18 g of a nonionic solute is dissolved in 36.30 g of benzene ($$K_f = 5.12\ ^\circ\mathrm{C}/m$$), and the freezing point is $$2.70\ ^\circ\mathrm{C} ($$benzene's normal freezing point is $$5.53\ ^\circ\mathrm{C}$$), what is the molar mass of the solute?

Accepted Answer

$$60.0\ \mathrm{g/mol}$$

Question 8

Which of the following best explains why the boiling point of a solution is higher than that of the pure solvent?

Accepted Answer

The presence of solute particles lowers the vapor pressure, requiring a higher temperature to reach atmospheric pressure.

Question 9

A solution is prepared by dissolving 29.7 g of $$\mathrm{Na_2SO_4} ($$molar mass = 142.04 g/mol) in 84.4 g of water. Assuming complete ionization, what is the boiling point of the solution? ($$K_b$$ for water = $$0.52\ ^\circ\mathrm{C}/m)$$

Accepted Answer

$$101.10\ ^\circ\mathrm{C}$$

Question 10

If a solute is only 80% dissociated in water, how would you calculate the van’t Hoff factor ($$i) $$for a solute that would otherwise produce 3 ions per formula unit?

Accepted Answer

$$i = 1 + 0.8 	imes (3 - 1) = 2.6$$

Question 11

A solution is made by dissolving 144 g of glucose ($$\mathrm{C_6H_{12}O_6$}$$, molar mass = 180.16 g/mol) in 1.0 kg of water. What is the freezing point of the solution? ($$K_f$$ for water = $$1.86\ ^\circ\mathrm{C}/m)$$

Accepted Answer

$$-1.49\ ^\circ\mathrm{C}$$

Question 12

Which of the following is NOT a colligative property?

Accepted Answer

Density

Question 13

A solution is prepared by dissolving 48 g of methanol ($$\mathrm{CH_3OH}$$, molar mass = 32.04 g/mol) in 200 g of water. What is the boiling point of the solution? ($$K_b$$ for water = $$0.52\ ^\circ\mathrm{C}/m)$$

Accepted Answer

$$100.78\ ^\circ\mathrm{C}$$

Question 14

If the freezing point of a water solution is $$-9.3\ ^\circ\mathrm{C}$$, what is the molality of the solution? ($$K_f$$ for water = $$1.86\ ^\circ\mathrm{C}/m)$$

Accepted Answer

$$5.0\ m$$

Question 15

A solution is made by dissolving 22.5 g of an unknown substance in 250 g of water, resulting in a freezing point of $$-0.930\ ^\circ\mathrm{C}. $$What is the molar mass of the unknown substance? ($$K_f$$ for water = $$1.86\ ^\circ\mathrm{C}/m)$$

Accepted Answer

$$180\ \mathrm{g/mol}$$

Question 16

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

Accepted Answer

The boiling point increases and the freezing point decreases.

Question 17

A solution is prepared by dissolving 100 g of ethylene glycol ($$\mathrm{C_2H_6O_2}$$, molar mass = 62.07 g/mol) in 200 g of water. What is the molality of the solution?

Accepted Answer

$$8.06\ m$$

Question 18

If the boiling point of a water solution is $$103.12\ ^\circ\mathrm{C}$$, what is the molality of the solution? ($$K_b$$ for water = $$0.52\ ^\circ\mathrm{C}/m)$$

Accepted Answer

$$6.0\ m$$

Question 19

Which of the following would have the highest boiling point, assuming equal molal concentrations in water?

Accepted Answer

$$\mathrm{$$CaCl_2$$}$$

Colligative Properties: Freezing Point Depression & Boiling Point Elevation – Step-by-Step Guidance

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