Q: A gas $$\mathrm{C_2F_4}$$ dissolves in water at 298 K to the extent of $$1.01 \times 10$$^{-3}$$\ \mathrm{M}$$ with a partial pressure of $$0.63\ \mathrm{atm}. $$What is the Henry’s Law constant $$k_H$$ for this gas at 298 K?

$$k_H = \dfrac{1.01 \times 10$$^{-3}$$\ \mathrm{M}}{0.63\ \mathrm{atm}} = 1.60 \times 10$$^{-3}$$\ \mathrm{mol\ L$$^{-1}$$\ $$atm^{-1}$$}$$

Q: Dissolving $$0.0250\ \mathrm{g} of$$ $$\beta-$$carotene (a non-electrolyte) in $$1.50\ \mathrm{g} of $$camphor causes a freezing point depression of $$1.17^\circ\mathrm{C}. If$$ $$K_f$$ for camphor is $$37.7^\circ\mathrm{C}/\mathrm{m}$$, what is the molar mass of $$\beta-$$carotene?

$$\dfrac{0.0250\ \mathrm{g}}{\left(\dfrac{1.17}{37.7} \times 0.00150\ \mathrm{kg}\right)} = 805\ \mathrm{g/mol}$$

Q: A person is considered to have lead poisoning if their blood contains more than $$10.0\ \mu\mathrm{g} of $$lead per dL. If $$\mathrm{$$PbCO_3$$}$$ has $$K_{sp} = 7.40 \times 10$$^{-14}$$, what is the maximum concentration of $$\mathrm{$$Pb^{2+}$$}$$ in water at equilibrium?

$$[\mathrm{Pb$$^{2+}$$}] = \sqrt{K_{sp}} = 8.60 \times 10$$^{-8}$$\ \mathrm{M}$$

Q: A $$25.0\ \mathrm{mL}$$ sample of $$0.752\ \mathrm{M}$$ monoprotic acid ($$\mathrm{HA}$$, $$K_a = 4.7 \times 10$$^{-8}$$) is titrated with 0.380$$\ \mathrm{M}$$ NaOH. What is the equivalence volume of NaOH required?

$$V_{\text{eq}} = \dfrac{0.0250\ \mathrm{L} \times 0.752\ \mathrm{M}}{0.380\ \mathrm{M}} = 0.0495\ \mathrm{L}$$

Q: A solution is made by dissolving $$7.42\ \mathrm{g} of $$niacin ($$\mathrm{C_6H_6NO_2}$$, non-electrolyte) in $$125.3\ \mathrm{g} of $$chloroform ($$\mathrm{$$CHCl_3$$}). If $$the vapor pressure of pure chloroform is $$94.4\ \mathrm{torr}$$, what is the vapor pressure of the solution?

$$P = 94.4\ \mathrm{torr} \times \dfrac{125.3/119.38}{(125.3/119.38)+(7.42/123.11)} = 89.7\ \mathrm{torr}$$

Q: The $$K_{sp} of$$ $$\mathrm{Ag_2SO_4} is$$ $$1.2 \times 10$$^{-5}$$. What is the solubility of $$\mathrm{Ag_2SO_4}$$ (in g/L, MW = 311.87$$\ \mathrm{g/mol}$$) in 0.0723$$\ \mathrm{M}$$ $$\mathrm{$$AgNO_3$$}$$?

$$s = \dfrac{K_{sp}}{(2 \times 0.0723)^2$} = 1.15 \times 10$$^{-3}$$\ \mathrm{mol/L} \times 311.87 = 0.36\ \mathrm{g/L}$$

Q: For the titration in the previous question, what is the equivalence volume of $$\mathrm{NaOH}$$ required?

$$V_{\text{eq}} = \dfrac{0.04500\ \mathrm{L} \times 0.700\ \mathrm{M}}{0.850\ \mathrm{M}} = 0.0371\ \mathrm{L}$$

Question 1

Which of the following substances would be most soluble in pentane ($$\mathrm{C_5H_{12}}$$)?

Accepted Answer

$$\mathrm{C$$_{10}$$H_{22}}$$

Question 2

Formation of solutions where $$\Delta H_{	ext{solution}} \u003e 0$$ can be spontaneous provided that:

Accepted Answer

They are accompanied by an increase in entropy

Question 3

How will the addition of $$\mathrm{HCl}$$ affect the solubility of the slightly soluble salt $$\mathrm{MgS}$$?

Accepted Answer

Increase

Question 4

A gas $$\mathrm{C_2F_4}$$ dissolves in water at 298 K to the extent of $$1.01 	imes 10$$^{-3}$$\ \mathrm{M}$$ with a partial pressure of $$0.63\ \mathrm{atm}. $$What is the Henry’s Law constant $$k_H$$ for this gas at 298 K?

Accepted Answer

$$k_H = \dfrac{1.01 	imes 10$$^{-3}$$\ \mathrm{M}}{0.63\ \mathrm{atm}} = 1.60 	imes 10$$^{-3}$$\ \mathrm{mol\ L$$^{-1}$$\ $$atm^{-1}$$}$$

Question 5

Dissolving $$0.0250\ \mathrm{g} of$$ $$\beta-$$carotene (a non-electrolyte) in $$1.50\ \mathrm{g} of $$camphor causes a freezing point depression of $$1.17^\circ\mathrm{C}. If$$ $$K_f$$ for camphor is $$37.7^\circ\mathrm{C}/\mathrm{m}$$, what is the molar mass of $$\beta-$$carotene?

Accepted Answer

$$\dfrac{0.0250\ \mathrm{g}}{\left(\dfrac{1.17}{37.7} 	imes 0.00150\ \mathrm{kg}ight)} = 805\ \mathrm{g/mol}$$

Question 6

Elemental analysis of $$\beta-$$carotene shows it contains $$10.51\% H $$and $$89.49\% C. $$What is the empirical formula of $$\beta-$$carotene?

Accepted Answer

$$\mathrm{C$$_{40}$$H_{56}}$$

Question 7

A person is considered to have lead poisoning if their blood contains more than $$10.0\ \mu\mathrm{g} of $$lead per dL. If $$\mathrm{$$PbCO_3$$}$$ has $$K_{sp} = 7.40 	imes 10$$^{-14}$$, what is the maximum concentration of $$\mathrm{$$Pb^{2+}$$}$$ in water at equilibrium?

Accepted Answer

$$[\mathrm{Pb$$^{2+}$$}] = \sqrt{K_{sp}} = 8.60 	imes 10$$^{-8}$$\ \mathrm{M}$$

Question 8

A $$25.0\ \mathrm{mL}$$ sample of $$0.752\ \mathrm{M}$$ monoprotic acid ($$\mathrm{HA}$$, $$K_a = 4.7 	imes 10$$^{-8}$$) is titrated with 0.380$$\ \mathrm{M}$$ NaOH. What is the equivalence volume of NaOH required?

Accepted Answer

$$V_{	ext{eq}} = \dfrac{0.0250\ \mathrm{L} 	imes 0.752\ \mathrm{M}}{0.380\ \mathrm{M}} = 0.0495\ \mathrm{L}$$

Question 9

At the equivalence point of the titration in the previous question, what is the pH of the solution?

Accepted Answer

$$\mathrm{pH} = 8.72$$

Question 10

A solution is made by dissolving $$7.42\ \mathrm{g} of $$niacin ($$\mathrm{C_6H_6NO_2}$$, non-electrolyte) in $$125.3\ \mathrm{g} of $$chloroform ($$\mathrm{$$CHCl_3$$}). If $$the vapor pressure of pure chloroform is $$94.4\ \mathrm{torr}$$, what is the vapor pressure of the solution?

Accepted Answer

$$P = 94.4\ \mathrm{torr} 	imes \dfrac{125.3/119.38}{(125.3/119.38)+(7.42/123.11)} = 89.7\ \mathrm{torr}$$

Question 11

The $$K_{sp} of$$ $$\mathrm{Ag_2SO_4} is$$ $$1.2 	imes 10$$^{-5}$$. What is the solubility of $$\mathrm{Ag_2SO_4}$$ (in g/L, MW = 311.87$$\ \mathrm{g/mol}$$) in 0.0723$$\ \mathrm{M}$$ $$\mathrm{$$AgNO_3$$}$$?

Accepted Answer

$$s = \dfrac{K_{sp}}{(2 	imes 0.0723)^2$} = 1.15 	imes 10$$^{-3}$$\ \mathrm{mol/L} 	imes 311.87 = 0.36\ \mathrm{g/L}$$

Question 12

A $$45.00\ \mathrm{mL}$$ sample of $$0.700\ \mathrm{M}$$ $$\mathrm{$$HNO_3$$} is $$titrated with $$0.850\ \mathrm{M}$$ $$\mathrm{NaOH}. $$What is the pH before any base is added?

Accepted Answer

$$\mathrm{pH} = -\log(0.700) = 0.155$$

Question 13

For the titration in the previous question, what is the equivalence volume of $$\mathrm{NaOH}$$ required?

Accepted Answer

$$V_{	ext{eq}} = \dfrac{0.04500\ \mathrm{L} 	imes 0.700\ \mathrm{M}}{0.850\ \mathrm{M}} = 0.0371\ \mathrm{L}$$

Question 14

After adding $$32.87\ \mathrm{mL} of$$ $$0.850\ \mathrm{M}$$ $$\mathrm{NaOH} to$$ $$45.00\ \mathrm{mL} of$$ $$0.700\ \mathrm{M}$$ $$\mathrm{$$HNO_3$$}$$, what is the pH of the solution?

Accepted Answer

The solution is still acidic; $$\mathrm{pH} = -\log\left(\dfrac{(0.700 	imes 0.04500) - (0.850 	imes 0.03287)}{0.04500 + 0.03287}ight) = 0.38$$

Question 15

After adding $$40.21\ \mathrm{mL} of$$ $$0.850\ \mathrm{M}$$ $$\mathrm{NaOH} to$$ $$45.00\ \mathrm{mL} of$$ $$0.700\ \mathrm{M}$$ $$\mathrm{$$HNO_3$$}$$, what is the pH of the solution?

Accepted Answer

The solution is basic; $$\mathrm{pOH} = -\log\left(\dfrac{(0.850 	imes 0.04021) - (0.700 	imes 0.04500)}{0.04500 + 0.04021}ight) = 1.36$$, $$\mathrm{pH} = 12.64$$

Question 16

Which of the following will NOT affect the solubility of $$\mathrm{MgS}$$?

Accepted Answer

$$\mathrm{$$NaNO_3$$}$$

Question 17

Which of the following best explains why adding $$\mathrm{HCl}$$ increases the solubility of $$\mathrm{MgS}$$?

Accepted Answer

The $$\mathrm{H^+}$$ from $$\mathrm{HCl}$$ reacts with $$\mathrm{S$$^{2-}$$} to $$form $$\mathrm{H_2S}$$, shifting the equilibrium to dissolve more $$\mathrm{MgS}.$$

Chem 112 Exam 3 – Step-by-Step Study Guidance

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