Q: According to Henry's Law, the solubility of a gas in a liquid is given by $S_g = k P_g$. If the solubility of $N_2$ in water at 25 $^\circ$C and 0.78 atm is $5.3 \times 10^{-4}$ M, what is the value of the Henry's Law constant $k$ for $N_2$ at this temperature?

$k = 6.8 \times 10^{-4} \, \frac{\text{mol}}{\text{L} \cdot \text{atm}}$

Q: A solution is prepared by dissolving 25.0 g of heptane (molar mass = 100 g/mol) and 35.0 g of octane (molar mass = 114 g/mol). If the vapor pressures of pure heptane and octane at the given temperature are 791 torr and 352 torr, respectively, what is the vapor pressure of the solution? (Assume ideal behavior.)

$P_{\text{solution}} = 553$ torr

Q: Which of the following is the correct formula for calculating the percent by mass of a component in a solution?

$\text{Percent by mass} = \frac{\text{mass of component}}{\text{total mass of solution}} \times 100\%$

Question 1

A non-volatile solute is dissolved in water at room temperature, forming a saturated solution. The solution is then heated until all the solid dissolves, and then cooled back to room temperature, where solid reappears. Which of the following best explains why solid reappears after cooling?

Accepted Answer

The solubility of most solids in water decreases as temperature decreases, so excess solute precipitates out.

Question 2

According to Henry's Law, the solubility of a gas in a liquid is given by $S_g = k P_g$. If the solubility of $N_2$ in water at 25 $^\circ$C and 0.78 atm is $5.3 	imes 10^{-4}$ M, what is the value of the Henry's Law constant $k$ for $N_2$ at this temperature?

Accepted Answer

$k = 6.8 	imes 10^{-4} \, \frac{	ext{mol}}{	ext{L} \cdot 	ext{atm}}$

Question 3

A can of soda is more 'bubbly' when opened straight from the refrigerator than when left out at room temperature. Which statement best explains this observation?

Accepted Answer

The solubility of $CO_2$ in water is higher at lower temperatures, so more gas is dissolved in cold soda.

Question 4

If the Henry's Law constant for $O_2$ at 25 $^\circ$C is $1.3 	imes 10^{-2}$ mol/(L·atm), and for $N_2$ it is $6.8 	imes 10^{-4}$ mol/(L·atm), which gas is more soluble in water at 1.0 atm and why?

Accepted Answer

$O_2$ is more soluble because it has a higher Henry's Law constant.

Question 5

At 25 $^\circ$C, the solubility of $CO_2$ in water is $1.45 	imes 10^{-3}$ M at a partial pressure of 1.00 atm. What would the solubility be at 3.2 atm, assuming Henry's Law applies?

Accepted Answer

$4.64 	imes 10^{-3}$ M

Question 6

Which of the following statements about the effect of pressure on solubility is correct?

Accepted Answer

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

Question 7

A solution is prepared by dissolving 25.0 g of heptane (molar mass = 100 g/mol) and 35.0 g of octane (molar mass = 114 g/mol). If the vapor pressures of pure heptane and octane at the given temperature are 791 torr and 352 torr, respectively, what is the vapor pressure of the solution? (Assume ideal behavior.)

Accepted Answer

$P_{	ext{solution}} = 553$ torr

Question 8

Which of the following best describes what happens to the vapor pressure of a solvent when a non-volatile solute is added?

Accepted Answer

The vapor pressure decreases because the mole fraction of the solvent is reduced.

Question 9

A 100. ppm solution of lead (Pb, MW = 207.2 g/mol) is prepared. What is the molarity of this solution?

Accepted Answer

$4.83 	imes 10^{-4}$ M

Question 10

Which of the following concentration units is independent of temperature?

Accepted Answer

Molality ($m$)

Question 11

A solution is prepared by dissolving 50.0 g of ethylene glycol (EG, MW = 62.07 g/mol) in 100.0 g of water. What is the molality of the solution?

Accepted Answer

$0.806$ m

Question 12

Which of the following best explains why the vapor pressure of a solution is always lower than that of the pure solvent when a non-volatile solute is added?

Accepted Answer

The presence of solute particles reduces the number of solvent molecules at the surface, decreasing the rate of evaporation.

Question 13

If the mole fraction of glucose in an aqueous solution is 0.10, what is the mole fraction of water?

Accepted Answer

0.90

Question 14

Which of the following statements about the effect of temperature on the solubility of gases in water is correct?

Accepted Answer

The solubility of gases in water decreases as temperature increases.

Question 15

A solution contains 1.0 mol of solute and 9.0 mol of solvent. What is the mole fraction of the solute?

Accepted Answer

0.10

Question 16

Which of the following is the correct formula for calculating the percent by mass of a component in a solution?

Accepted Answer

$	ext{Percent by mass} = \frac{	ext{mass of component}}{	ext{total mass of solution}} 	imes 100\%$

Question 17

Which of the following best describes the relationship between vapor pressure and boiling point for a liquid?

Accepted Answer

A liquid with a lower boiling point has a higher vapor pressure at a given temperature.

Question 18

Which of the following is the correct expression for Raoult's Law for a solution containing a non-volatile solute?

Accepted Answer

$P_{	ext{solution}} = X_{	ext{solvent}} P_{	ext{solvent}}^\circ$

Question 19

A solution is prepared by dissolving 10.0 g of NaCl (molar mass = 58.44 g/mol) in 500.0 g of water. What is the molality of the solution?

Accepted Answer

$0.342$ m

Solubility and Vapor Pressure in Solutions: Effects of Pressure and Temperature

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