Q: A $$0.50\ \mathrm{mol/L}$$ solution of glucose ($$\mathrm{C_6H_{12}O_6$}) is $$separated from pure water by a semipermeable membrane. What is the osmotic pressure ($$\Pi) at$$ $$25^\circ\mathrm{C}$$? ($$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

$$\Pi = 0.50 \times 0.0821 \times 298 = 12.2\ \mathrm{atm}$$

Q: A $$2.00\ \mathrm{mol}$$ sample of NaCl is dissolved in $$1.00\ \mathrm{kg} of $$water. If the freezing point depression constant for water is $$K_f = 1.86\ ^\circ\mathrm{C\cdot kg\cdot $$mol^{-1}$$}$$, what is the expected freezing point depression ($$\Delta T_f$$)? (Assume complete dissociation.)

$$\Delta T_f = 1.86 \times 2 \times 2 = 7.44^\circ\mathrm{C}$$

Question 1

Which of the following best explains why water has a much higher boiling point than methane ($$\mathrm{CH_4$}$$), even though both are small molecules?

Accepted Answer

Water molecules form hydrogen bonds, which are much stronger than the London dispersion forces present in methane.

Question 2

A sample of ethanol ($$\mathrm{C_2H_5OH}) is $$heated from $$20^\circ\mathrm{C} to$$ $$80^\circ\mathrm{C}$$, then completely vaporized at its boiling point ($$78^\circ\mathrm{C}). $$Which of the following steps requires the most energy?

Accepted Answer

Vaporizing the ethanol at $$78^\circ\mathrm{C}.$$

Question 3

Which of the following substances would you expect to have the highest viscosity at room temperature?

Accepted Answer

Glycerol ($$\mathrm{C_3H_8O_3}$$), due to its extensive hydrogen bonding.

Question 4

A solution is prepared by dissolving $$10.0\ \mathrm{g} of $$NaCl in $$100.0\ \mathrm{g} of $$water. What is the molality ($$m) of $$the solution? ($$\mathrm{M_{NaCl}} = 58.44\ \mathrm{g/mol})$$

Accepted Answer

$$m = \dfrac{10.0\ \mathrm{g} / 58.44\ \mathrm{g/mol}}{0.1000\ \mathrm{kg}} = 1.71\ \mathrm{mol/kg}$$

Question 5

Which of the following best describes a supersaturated solution?

Accepted Answer

A solution that contains more dissolved solute than is normally possible at a given temperature.

Question 6

Which of the following compounds will have the highest boiling point elevation when $$1.0\ \mathrm{mol} is $$dissolved in $$1.0\ \mathrm{kg} of $$water? (Assume complete dissociation.)

Accepted Answer

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

Question 7

A phase diagram for carbon dioxide shows that at $$1\ \mathrm{atm}$$ and $$-78.5^\circ\mathrm{C}$$, solid CO$$_2$$ sublimes directly to gas. What does this indicate about the triple point of CO$$_2$$?

Accepted Answer

The triple point of CO$$_2 is $$below $$1\ \mathrm{atm}.$$

Question 8

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

Accepted Answer

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

Question 9

A $$0.50\ \mathrm{mol/L}$$ solution of glucose ($$\mathrm{C_6H_{12}O_6$}) is $$separated from pure water by a semipermeable membrane. What is the osmotic pressure ($$\Pi) at$$ $$25^\circ\mathrm{C}$$? ($$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

Accepted Answer

$$\Pi = 0.50 	imes 0.0821 	imes 298 = 12.2\ \mathrm{atm}$$

Question 10

Which of the following statements about vapor pressure is correct?

Accepted Answer

Vapor pressure increases as temperature increases because more molecules have enough energy to escape the liquid phase.

Question 11

A $$2.00\ \mathrm{mol}$$ sample of NaCl is dissolved in $$1.00\ \mathrm{kg} of $$water. If the freezing point depression constant for water is $$K_f = 1.86\ ^\circ\mathrm{C\cdot kg\cdot $$mol^{-1}$$}$$, what is the expected freezing point depression ($$\Delta T_f$$)? (Assume complete dissociation.)

Accepted Answer

$$\Delta T_f = 1.86 	imes 2 	imes 2 = 7.44^\circ\mathrm{C}$$

Question 12

Which of the following best describes the process of dissolving NaCl in water?

Accepted Answer

The positive ends of water molecules surround Cl$$^-$$ ions, and the negative ends surround Na$$^+$$ ions, stabilizing them in solution.

Question 13

Which of the following is the correct expression for the mole fraction ($$X_A) of $$component A in a solution?

Accepted Answer

$$X_A = \dfrac{	ext{mol A}}{	ext{total mol in solution}}$$

Question 14

A solution is made by dissolving $$5.00\ \mathrm{g} of $$KNO$$_3 in$$ $$95.0\ \mathrm{g} of $$water. What is the mass percentage of KNO$$_3 in $$the solution?

Accepted Answer

$$\dfrac{5.00}{5.00 + 95.0} 	imes 100 = 5.00\%$$

Question 15

Which of the following statements about surface tension is correct?

Accepted Answer

Surface tension is higher in liquids with strong intermolecular forces.

Question 16

Which of the following best describes the effect of increasing pressure on the solubility of a gas in a liquid?

Accepted Answer

Increasing pressure increases the solubility of a gas in a liquid.

Question 17

A solution is prepared by mixing $$0.20\ \mathrm{mol} of $$benzene and $$0.80\ \mathrm{mol} of $$toluene. If the vapor pressure of pure benzene is $$100\ \mathrm{mmHg} at a $$certain temperature, what is the partial vapor pressure of benzene in the solution? (Use Raoult's Law.)

Accepted Answer

$$P_{	ext{benzene}} = 100 	imes \dfrac{0.20}{1.00} = 20\ \mathrm{mmHg}$$

Question 18

Which of the following is the correct formula for calculating molarity ($$M$$)?

Accepted Answer

$$M = \dfrac{	ext{mol solute}}{	ext{L solution}}$$

Question 19

A patient receives an intravenous solution with a higher concentration of solute than their blood plasma. What will happen to the patient's red blood cells due to osmosis?

Accepted Answer

Water will leave the red blood cells, causing them to shrink (crenate).

Properties of Liquids and Solids, Intermolecular Forces, and Solutions

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