Q: A sample of gas occupies 20.5 L at 737 torr and constant temperature. If the pressure is increased to 1.80 atm, what will be the new volume of the gas? (1 atm = 760 torr)

$$V_2$$ = $$V_1$$ \times \frac{$$P_1$$}{$$P_2$$} = 20.5\,\mathrm{L} \times \frac{737\,\mathrm{torr}}{1.80 \times 760\,\mathrm{torr}} = 11.0\,\mathrm{L}$$

Q: A 50.0 g sample of ice at 0$$^\circC is $$heated to liquid water at 22$$^\circC. $$Given $$\Delta H_{fus} = 6.0\,\mathrm{kJ/mol}$$ and $$C_s = 4.184\,\mathrm{J/g\cdot ^\circ C}$$, how much heat (in kJ) is required? (Molar mass of H$$_2O = 18.0 g/$$mol)

$$Q = n\Delta H_{fus} + mC_s\Delta T = 2.78\,\mathrm{mol} \times 6.0\,\mathrm{kJ/mol} + 50.0\,\mathrm{g} \times 4.184\,\mathrm{J/g\cdot ^\circ C} \times 22^\circ\mathrm{C} = 16.7\,\mathrm{kJ} + 4.6\,\mathrm{kJ} = 21.3\,\mathrm{kJ}$$

Q: A solution is prepared by dissolving 11.3 g of Ca(NO$$_3$$)$$_2 ($$molar mass = 164 g/mol) in 115 g of water. What is the freezing point of the solution? ($$K_f = 1.86^\circ\mathrm{C}/m$$, $$i = 3$$ for Ca(NO$$_3$$)$$_2)$$

$$\Delta T_f = i K_f m = 3 \times 1.86 \times \frac{11.3/164}{0.115} = 3 \times 1.86 \times 0.595 = 3.32^\circ\mathrm{C}$$; Freezing point = $$0 - 3.32 = -3.32^\circ\mathrm{C}$$

Q: A 4.71 L sample of water (density = 1.00 g/mL) is mixed with 0.290 L of ethylene glycol (C$$_2H$_6O$_2$$, density = 1.12 g/mL). What is the freezing point of the mixture? ($$K_f = 1.86^\circ\mathrm{C}/m$$; molar mass of C$$_2H$_6O$_2 = 62.1 g/$$mol)

Freezing point = $$0 - (1.86 \times \frac{324.8/62.1}{4710}) = -2.06^\circ\mathrm{C}$$

Q: The Henry's law constant for CO$$_2 is$$ $$3.1 \times 10$$^{-2}$$ mol/L·atm at 25$$^\circ$$C. What pressure is required to achieve a 0.25 M solution?

$$P = \frac{C}{k_H} = \frac{0.25}{3.1 \times 10$$^{-2}$$} = 8.1\,\mathrm{atm}$$

Q: A balloon originally has a volume of 4.39 L at 44$$^\circC $$and 729 torr. To what temperature (in $$^\circC) $$must the balloon be cooled to reduce its volume to 3.78 L at constant pressure?

$$T_2$$ = $$T_1$$ \times \frac{$$V_2$$}{$$V_1$$} = (44 + 273) \times \frac{3.78}{4.39} = 317 \times 0.861 = 273\,\mathrm{K} = 0^\circ\mathrm{C}$$

Question 1

A sample of gas occupies 20.5 L at 737 torr and constant temperature. If the pressure is increased to 1.80 atm, what will be the new volume of the gas? (1 atm = 760 torr)

Accepted Answer

$$V_2$$ = $$V_1$$ 	imes \frac{$$P_1$$}{$$P_2$$} = 20.5\,\mathrm{L} 	imes \frac{737\,\mathrm{torr}}{1.80 	imes 760\,\mathrm{torr}} = 11.0\,\mathrm{L}$$

Question 2

Which of the following molecules can form hydrogen bonds between like molecules?

Accepted Answer

(CH$$_3$$)$$_2NH$$

Question 3

A 50.0 g sample of ice at 0$$^\circC is $$heated to liquid water at 22$$^\circC. $$Given $$\Delta H_{fus} = 6.0\,\mathrm{kJ/mol}$$ and $$C_s = 4.184\,\mathrm{J/g\cdot ^\circ C}$$, how much heat (in kJ) is required? (Molar mass of H$$_2O = 18.0 g/$$mol)

Accepted Answer

$$Q = n\Delta H_{fus} + mC_s\Delta T = 2.78\,\mathrm{mol} 	imes 6.0\,\mathrm{kJ/mol} + 50.0\,\mathrm{g} 	imes 4.184\,\mathrm{J/g\cdot ^\circ C} 	imes 22^\circ\mathrm{C} = 16.7\,\mathrm{kJ} + 4.6\,\mathrm{kJ} = 21.3\,\mathrm{kJ}$$

Question 4

Which intermolecular force is primarily responsible for the high surface tension of water, allowing some insects to walk on its surface?

Accepted Answer

Hydrogen bonding

Question 5

Which of the following pairs is more likely to be soluble in hexane ($$\mathrm{C_6H_{14}}$$)?

Accepted Answer

CCl$$_4$$

Question 6

A solution is prepared by dissolving 11.3 g of Ca(NO$$_3$$)$$_2 ($$molar mass = 164 g/mol) in 115 g of water. What is the freezing point of the solution? ($$K_f = 1.86^\circ\mathrm{C}/m$$, $$i = 3$$ for Ca(NO$$_3$$)$$_2)$$

Accepted Answer

$$\Delta T_f = i K_f m = 3 	imes 1.86 	imes \frac{11.3/164}{0.115} = 3 	imes 1.86 	imes 0.595 = 3.32^\circ\mathrm{C}$$; Freezing point = $$0 - 3.32 = -3.32^\circ\mathrm{C}$$

Question 7

Which gas will effuse faster through a pinhole: CO$$_2 or O$_2$$? By what factor?

Accepted Answer

O$$_2$$ will effuse faster; $$\sqrt{\frac{M_{CO_2$}}{M_{O_2$}}} = \sqrt{\frac{44}{32}} = 1.17$$ times faster

Question 8

What is the osmotic pressure (in atm) of a solution formed by dissolving 89.5 mg of aspirin (C$$_9H$_8O$_4$$, molar mass = 180 g/mol) in 0.500 L of water at 25$$^\circC$$? ($$R = 0.0821 L$$·atm/mol·K)

Accepted Answer

$$\Pi = MRT = \frac{0.0895\,\mathrm{g}}{180\,\mathrm{g/mol} 	imes 0.5\,\mathrm{L}} 	imes 0.0821 	imes 298 = 0.0297\,\mathrm{atm}$$

Question 9

Which of the following best explains why the boiling point of CH$$_3$$OCH$$_3 is $$higher than that of C$$_3H$_8$$?

Accepted Answer

CH$$_3$$OCH$$_3$$ has dipole-dipole forces in addition to London dispersion forces, while C$$_3H$_8$$ only has London dispersion forces.

Question 10

A 4.71 L sample of water (density = 1.00 g/mL) is mixed with 0.290 L of ethylene glycol (C$$_2H$_6O$_2$$, density = 1.12 g/mL). What is the freezing point of the mixture? ($$K_f = 1.86^\circ\mathrm{C}/m$$; molar mass of C$$_2H$_6O$_2 = 62.1 g/$$mol)

Accepted Answer

Freezing point = $$0 - (1.86 	imes \frac{324.8/62.1}{4710}) = -2.06^\circ\mathrm{C}$$

Question 11

The Henry's law constant for CO$$_2 is$$ $$3.1 	imes 10$$^{-2}$$ mol/L·atm at 25$$^\circ$$C. What pressure is required to achieve a 0.25 M solution?

Accepted Answer

$$P = \frac{C}{k_H} = \frac{0.25}{3.1 	imes 10$$^{-2}$$} = 8.1\,\mathrm{atm}$$

Question 12

What is the limiting value of the van’t Hoff factor ($$i) $$for Na$$_2CO$_3$$?

Accepted Answer

$$i = 3$$

Question 13

A balloon originally has a volume of 4.39 L at 44$$^\circC $$and 729 torr. To what temperature (in $$^\circC) $$must the balloon be cooled to reduce its volume to 3.78 L at constant pressure?

Accepted Answer

$$T_2$$ = $$T_1$$ 	imes \frac{$$V_2$$}{$$V_1$$} = (44 + 273) 	imes \frac{3.78}{4.39} = 317 	imes 0.861 = 273\,\mathrm{K} = 0^\circ\mathrm{C}$$

Question 14

Which of the following best describes a supersaturated solution?

Accepted Answer

A solution that contains more solute than is present in a saturated solution at a given temperature.

Question 15

Which of the following statements about phase diagrams is correct?

Accepted Answer

The critical point is the temperature and pressure above which the liquid and gas phases are indistinguishable.

Question 16

Which of the following best explains why CaCl$$_2 is $$much more soluble in water than in hexane?

Accepted Answer

Water forms strong ion-dipole interactions with Ca$$^{2+}$$ and Cl$$^-$$ ions.

Question 17

Which of the following is NOT a colligative property?

Accepted Answer

Viscosity

Question 18

A gas at constant pressure has a temperature of 22$$^\circC $$and a volume of 55.60 L. What will the volume be if the temperature is increased to 38$$^\circC$$?

Accepted Answer

$$V_2$$ = $$V_1$$ 	imes \frac{$$T_2$$}{$$T_1$$} = 55.60 	imes \frac{311}{295} = 58.6\,\mathrm{L}$$

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