Q: A solution is prepared by mixing 50.0 mL of ethanol (density = 0.789 g/mL) with 100.0 mL of water (density = 1.00 g/mL). What is the mass percent of ethanol in the solution?

$$\text{Mass percent} = \frac{39.45\,g}{139.45\,g} \times 100\% = 28.3\%$$

Question 1

Which of the following best explains why wood frogs can survive freezing temperatures while most other cold-blooded animals cannot?

Accepted Answer

Wood frogs have a high concentration of glucose in their blood, which lowers the freezing point of their bodily fluids.

Question 2

Which vitamin structure shown is most likely to be water soluble, and why?

Accepted Answer

The first structure, because it contains multiple -OH groups capable of hydrogen bonding with water.

Question 3

A solution is prepared by dissolving 10.0 g of NaCl (molar mass = 58.44 g/mol) in enough water to make 500 mL of solution. What is the molarity of the solution?

Accepted Answer

$$M = \frac{10.0\,g}{58.44\,g/mol} \div 0.500\,L = 0.342\,M$$

Question 4

Which of the following statements about the process of solution formation is correct?

Accepted Answer

Overcoming solute-solute and solvent-solvent attractions are both endothermic processes.

Question 5

Which of the following best describes a saturated solution?

Accepted Answer

A solution in which the solute and solvent are in dynamic equilibrium and no more solute will dissolve at that temperature.

Question 6

Which of the following concentration units does NOT change with temperature?

Accepted Answer

Molality ($$m)$$

Question 7

A 0.200 m solution of NaCl is prepared using 0.200 mol NaCl and 1.00 kg of water. What is the mole fraction of NaCl in the solution? (Moles of water = 55.5 mol)

Accepted Answer

$$X_{NaCl} = \frac{0.200}{0.200 + 55.5} = 0.0036$$

Question 8

Which of the following best explains why adding salt to ice lowers the freezing point of water?

Accepted Answer

The dissolved salt particles disrupt the equilibrium between ice and liquid water, requiring a lower temperature for freezing.

Question 9

A solution is made by dissolving 2.00 g of KNO$$_3 ($$molar mass = 101.1 g/mol) in 100.0 g of water. What is the molality of the solution?

Accepted Answer

$$m = \frac{2.00\,g}{101.1\,g/mol} \div 0.100\,kg = 0.198\,m$$

Question 10

Which of the following is a correct application of Henry’s Law?

Accepted Answer

The solubility of a gas in a liquid increases as the partial pressure of the gas above the liquid increases.

Question 11

A solution is prepared by mixing 50.0 mL of ethanol (density = 0.789 g/mL) with 100.0 mL of water (density = 1.00 g/mL). What is the mass percent of ethanol in the solution?

Accepted Answer

$$	ext{Mass percent} = \frac{39.45\,g}{139.45\,g} 	imes 100\% = 28.3\%$$

Question 12

Which of the following best describes the effect of a nonvolatile solute on the vapor pressure of a solvent?

Accepted Answer

The vapor pressure of the solvent decreases because solute particles occupy surface positions, reducing the rate of vaporization.

Question 13

Calculate the freezing point of a solution made by dissolving 0.500 mol of NaCl in 1.00 kg of water. ($$K_f$$ for water = $$1.86\, ^\circ C/m$$; assume complete dissociation of NaCl.)

Accepted Answer

$$\Delta T_f = i \cdot m \cdot K_f = 2 \cdot 0.500 \cdot 1.86 = 1.86\, ^\circ C$$; 
ewline 	ext{Freezing point} = 0.00 - 1.86 = -1.86\, ^\circ C$

Question 14

Which of the following best describes a hyperosmotic (hypertonic) solution with respect to a red blood cell?

Accepted Answer

It has a higher osmotic pressure than the cell, causing water to flow out and the cell to shrivel.

Question 15

A solution is prepared by dissolving 0.10 mol of glucose (a nonelectrolyte) in 1.0 L of water at 25°C. What is the osmotic pressure of the solution? ($$R = 0.08206\, 	ext{L} \cdot 	ext{atm} / 	ext{mol} \cdot K$$, $$T = 298\,K)$$

Accepted Answer

$$\Pi = MRT = 0.10 \cdot 0.08206 \cdot 298 = 2.45\,atm$$

Question 16

Which of the following best explains why carbonated beverages lose their fizz faster when warm than when cold?

Accepted Answer

The solubility of CO$$_2 in $$water decreases as temperature increases, causing more gas to escape.

Question 17

Which of the following is a colligative property?

Accepted Answer

Osmotic pressure

Chapter 13: Solutions and Their Properties – General Chemistry Study Notes

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