Q: A solution is made by dissolving 0.75 moles of nonvolatile safrole in 950 g of ethanol at 25°C. What is the vapor pressure of the solution? (Vapor pressure of pure ethanol at 25°C is 50.0 torr; molar mass of ethanol is 46.07 g/mole) Use: $$P_{solution} = X_{solvent} \times P^0$_{solvent}$$

$$P_{solution} = 46.7\,\text{torr}$$

Question 1

A solution is prepared by dissolving a nonvolatile solute in water at 35°C. If the vapor pressure of pure water at this temperature is 42.2 mmHg, and the solution's vapor pressure is 37.1 mmHg, what is the mole fraction of water in the solution?

Use the formula: 
$$P_{solution} = X_{solvent} 	imes P^0$_{solvent}$$

Accepted Answer

$$X_{water} = 0.879$$

Question 2

Which of the following solutions will have the lowest freezing point? Assume complete dissociation for strong electrolytes and that all solutions are made with the same amount of solvent.

a) $$0.4\,m$$ NaCl
b) $$0.3\,m Na_2SO_4
c$$) $$0.5\,m$$ sucrose (nonelectrolyte)

Accepted Answer

b) $$0.3\,m Na$_2SO$_4$$

Question 3

A solution is made by dissolving 0.75 moles of nonvolatile safrole in 950 g of ethanol at 25°C. What is the vapor pressure of the solution? (Vapor pressure of pure ethanol at 25°C is 50.0 torr; molar mass of ethanol is 46.07 g/mole)

Use: $$P_{solution} = X_{solvent} 	imes P^0$_{solvent}$$

Accepted Answer

$$P_{solution} = 46.7\,	ext{torr}$$

Question 4

When 0.0250 g of $$\beta-$$carotene is dissolved in 1.50 g of liquid camphor, the freezing point of the mixture is 178.6°C. The freezing point constant for camphor is $$40.0\,^{\circ}\mathrm{C}/m$$, and the melting point of pure camphor is 179.8°C. What is the molar mass of $$\beta-$$carotene?

Use: $$\Delta T_f = K_f 	imes m$$

Accepted Answer

$$M = 6600\,	ext{g/mole}$$

Question 5

Which of the following solutions will have the highest boiling point? Assume all salts are strong electrolytes unless otherwise indicated.

a) $$0.2\,m$$ HCl
b) $$0.2\,m$$ acetic acid (weak electrolyte)
c) $$0.3\,m$$ KOH

Accepted Answer

c) $$0.3\,m$$ KOH

Question 6

How many grams of sucrose ($$\mathrm{C}_{12}\mathrm{H}_{22}\mathrm{O}_{11}) $$must be added to 552 g of water to lower the vapor pressure by 2.00 mmHg at 20°C? (Vapor pressure of water at 20°C is 17.5 mmHg; molar mass of sucrose is 342.3 g/mole; water is 18.02 g/mole)

Use: $$\Delta P = X_{solute} 	imes P^0$_{solvent}$$

Accepted Answer

108 g

Question 7

A solution is prepared by dissolving 678 g of glucose (molar mass = 180.2 g/mole) in 2.0 kg of water. What is the boiling point of the solution? ($$K_b$$ for water = $$0.52\,^{\circ}\mathrm{C}/m$$; water boils at $$100.0^{\circ}$$\mathrm{C}$$)

Use: $$\Delta T_b = K_b 	imes m$$

Accepted Answer

$$101.0^{\circ}$$\mathrm{C}$$

Question 8

What mass of naphthalene (molar mass = 128.2 g/mole) must be dissolved in 200. g of benzene to lower the freezing point by $$2.50^{\circ}$$\mathrm{C}$$? (K_f$ for benzene = 5.12$$^{\circ}$$\mathrm{C}/m)

$$Use: $$\Delta T_f = K_f 	imes m$$

Accepted Answer

12.5 g

Question 9

A 50.0 mL solution of insulin has an osmotic pressure of 16.8 mmHg at 25°C. What mass of insulin (molar mass = 5734 g/mole) is present? ($$R = 0.08206\,\mathrm{L\,atm/(mol\,K)}$$, $$T = 298\,\mathrm{K}$$, $$1\,\mathrm{atm} = 760\,\mathrm{mmHg})

$$Use: $$\Pi = MRT$$

Accepted Answer

0.026 g

Question 10

Which of the following solutions will have the lowest boiling point? Assume all are nonelectrolytes.

a) $$0.5\,m$$ ethylene glycol
b) $$0.4\,m$$ glucose
c) $$0.3\,m$$ BaCl$$_2$$

Accepted Answer

b) $$0.4\,m$$ glucose

Question 11

A solution is made by dissolving a nonvolatile solute in water, causing the vapor pressure to decrease. Which of the following best explains why the vapor pressure decreases?

Accepted Answer

The solute particles occupy surface sites, reducing the number of water molecules able to escape into the vapor phase.

Question 12

A solution is prepared by dissolving 678 g of glucose in 2.0 kg of water. What is the freezing point of the solution? ($$K_f$$ for water = $$1.86\,^{\circ}\mathrm{C}/m$$; water freezes at $$0.0^{\circ}$$\mathrm{C}$$)

Use: $$\Delta T_f = K_f 	imes m$$

Accepted Answer

$$-3.5^{\circ}$$\mathrm{C}$$

Question 13

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 14

A solution is made by dissolving a strong electrolyte in water. Compared to a solution with the same molality of a nonelectrolyte, which property will be greater for the electrolyte solution?

Accepted Answer

Boiling point elevation

Question 15

Which of the following best describes why adding salt to icy roads helps melt the ice?

Accepted Answer

Salt lowers the freezing point of water, causing ice to melt at lower temperatures.

Question 16

Which of the following would produce the greatest osmotic pressure at the same concentration and temperature?

Accepted Answer

A solution of Na$$_2SO$_4 ($$strong electrolyte)

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