Q: A solution is prepared by dissolving 4.6 g of NaCl in 500 g of water. What is the mass percent of NaCl in the solution? (Round to two decimal places)

$\frac{4.6}{504.6} \times 100\% = 0.91\%$

Q: A 0.400 m aqueous solution of NaCl (assume complete dissociation) is prepared. What is the expected freezing point of the solution? ($K_f$ for water = $1.86\ ^\circ$C m$^{-1}$)

$\Delta T_f = i K_f m = 2 \times 1.86 \times 0.400 = 1.488\ ^\circ$C;\newline T_f = 0.00 - 1.49 = -1.49\ ^\circ$C

Question 1

Which of the following statements best explains why NaCl dissolves readily in water but not in benzene?

Accepted Answer

NaCl is ionic and water is polar, so strong ion-dipole interactions stabilize the ions in solution.

Question 2

A solution is prepared by dissolving 4.6 g of NaCl in 500 g of water. What is the mass percent of NaCl in the solution? (Round to two decimal places)

Accepted Answer

$\frac{4.6}{504.6} 	imes 100\% = 0.91\%$

Question 3

Which of the following best describes the process of solvation?

Accepted Answer

The process by which solvent molecules surround and stabilize solute particles.

Question 4

A 0.100 m aqueous solution of MgCl$_2$ is prepared. Assuming complete dissociation, what is the van't Hoff factor $i$ for this solution?

Accepted Answer

$i = 3$

Question 5

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

Accepted Answer

Decreasing the temperature and increasing the pressure.

Question 6

A solution is made by dissolving 17.2 g of ethylene glycol (C$_2$H$_6$O$_2$, molar mass = 62.07 g/mol) in 0.500 kg of water. What is the molality of the solution?

Accepted Answer

$\frac{17.2}{62.07} = 0.277$ mol; $m = \frac{0.277}{0.500} = 0.554$ m

Question 7

Which of the following best describes a colloid?

Accepted Answer

A mixture with intermediate-sized particles that do not settle upon standing and scatter light.

Question 8

A 0.400 m aqueous solution of NaCl (assume complete dissociation) is prepared. What is the expected freezing point of the solution? ($K_f$ for water = $1.86\ ^\circ$C m$^{-1}$)

Accepted Answer

$\Delta T_f = i K_f m = 2 	imes 1.86 	imes 0.400 = 1.488\ ^\circ$C;
ewline T_f = 0.00 - 1.49 = -1.49\ ^\circ$C

Question 9

Which of the following concentration units is temperature independent?

Accepted Answer

Molality ($m$)

Question 10

A solution is prepared by mixing 22 g of toluene (C$_7$H$_8$) and 78 g of benzene (C$_6$H$_6$). The vapor pressures of pure toluene and benzene at 25$^\circ$C are 28.4 mmHg and 95.1 mmHg, respectively. What is the total vapor pressure above the solution? (Molar masses: C$_7$H$_8$ = 92.13 g/mol, C$_6$H$_6$ = 78.11 g/mol)

Accepted Answer

$P_{total} = X_{benzene} P^\circ_{benzene} + X_{toluene} P^\circ_{toluene} = 0.6389 	imes 95.1 + 0.3611 	imes 28.4 = 71.02$ mmHg

Question 11

Which of the following best explains why adding a non-volatile solute to a solvent lowers the vapor pressure of the solvent?

Accepted Answer

The solute blocks some of the surface area, reducing the number of solvent molecules that can escape into the vapor phase.

Question 12

A solution is prepared by dissolving 38.9 mg of caffeine (molar mass = 194.2 g/mol) in 355 mL of Pepsi (density = 1.01 g/mL). What is the concentration of caffeine in ppm (parts per million by mass)?

Question 13

Which of the following is a colligative property?

Accepted Answer

Boiling point elevation

Question 14

A solution is prepared by dissolving 0.350 g of a nonelectrolyte in 15.0 g of water, and the freezing point is lowered by 0.12$^\circ$C. What is the molar mass of the compound? ($K_f$ for water = $1.86\ ^\circ$C m$^{-1}$)

Accepted Answer

$m = \frac{\Delta T_f}{K_f} = \frac{0.12}{1.86} = 0.0645$ m;
ewline $mol = 0.0645 	imes 0.015 = 0.0009675$ mol;
ewline $MM = \frac{0.350}{0.0009675} = 362$ g/mol

Question 15

Which of the following best describes the Tyndall effect?

Accepted Answer

The scattering of light by particles in a colloid.

Question 16

A solution is isotonic with seawater if it has the same osmotic pressure. If the osmotic pressure of seawater is 30.0 atm at 25$^\circ$C, what is the molarity of an aqueous sucrose (C$_{12}$H$_{22}$O$_{11}$) solution that is isotonic with seawater? ($R = 0.08206$ L atm mol$^{-1}$ K$^{-1}$)

Accepted Answer

$\Pi = MRT ightarrow M = \frac{\Pi}{RT} = \frac{30.0}{0.08206 	imes 298} = 1.22$ M

Question 17

Which of the following best explains why ethylene glycol is used as antifreeze in car radiators?

Accepted Answer

It lowers the freezing point and raises the boiling point of water due to colligative properties.

Question 18

A solution is prepared by dissolving 0.100 mol of urea (a nonvolatile solute) in 1.00 kg of water. The vapor pressure of pure water at 25$^\circ$C is 23.8 mmHg. What is the vapor pressure of the solution? (Assume ideal behavior, molar mass of water = 18.02 g/mol)

Accepted Answer

$n_{H_2O} = \frac{1000}{18.02} = 55.5$ mol; $X_{H_2O} = \frac{55.5}{55.5+0.1} = 0.9982$; $P = 0.9982 	imes 23.8 = 23.76$ mmHg

Chapter 11: Solutions and Colloids – General Chemistry Study Notes

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