Q: Given the equilibrium $$\mathrm{N_2$(g) + O_2$(g) \rightleftharpoons 2NO(g)}$$ with $$K_c = 5.5 \times 10$$^{-4}$$, and equilibrium concentrations $$[\mathrm{$$N_2$$}] = 0.040\ \mathrm{M}$$ and $$[\mathrm{$$O_2$$}] = 0.0092\ \mathrm{M}$$, what is the equilibrium concentration of $$\mathrm{NO}$$?

$$[NO] = \sqrt{K_c \times [N_2$][O_2$]} = 0.0142\ \mathrm{M}$$

Q: For the weak acid $$\mathrm{HCN}$$, with $$K_a = 4.9 \times 10$$^{-10}$$ and an initial concentration of 0.15$$\ \mathrm{M}$$, what is the equilibrium concentration of $$\mathrm{H^+}$$?

$$[H^+] = \sqrt{K_a \times [HCN]_0} = 8.57 \times 10$$^{-6}$$\ \mathrm{M}$$

Q: The molar solubility of $$\mathrm{Ag_2SO_4} in $$pure water is $$1.2 \times 10$$^{-5}$$\ \mathrm{M}. $$What is the value of $$K_{sp}$$?

$$K_{sp} = 4 \times (1.2 \times 10$$^{-5}$$)^3 = 6.9$$ \times $$10^{-15}$

Q: A buffer solution is prepared by mixing $$0.250\ \mathrm{mol} of $$formic acid ($$K_a = 1.8 \times 10$$^{-4}$$) and 0.700$$\ \mathrm{mol}$$ of sodium formate in 1.00$$\ \mathrm{L}$$ of water. What is the pH of the buffer?

$$\mathrm{pH} = \mathrm{p}K_a + \log\left(\dfrac{[\text{formate}]}{[\text{formic acid}] }\right) = 4.74 + \log\left(\dfrac{0.700}{0.250}\right) = 5.18$$

Question 1

For the reaction $$\mathrm{I_2$(aq) + I^-(aq) ightleftharpoons I_3$^-(aq)}$$, if the initial concentrations of $$\mathrm{I_2$}$$ and $$\mathrm{I^-}$$ are both $$1.5 	imes 10$$^{-3}$$\ \mathrm{M}$$, and at equilibrium the concentration of $$\mathrm{I_2$} is$$ $$7.5 	imes 10$$^{-4}$$\ \mathrm{M}$$, what is the equilibrium constant $$K$$ for the reaction?

Accepted Answer

$$K = \dfrac{[I_3$^-]}{[I_2$][I^-]} = 0.44$$

Question 2

Given the equilibrium $$\mathrm{N_2$(g) + O_2$(g) ightleftharpoons 2NO(g)}$$ with $$K_c = 5.5 	imes 10$$^{-4}$$, and equilibrium concentrations $$[\mathrm{$$N_2$$}] = 0.040\ \mathrm{M}$$ and $$[\mathrm{$$O_2$$}] = 0.0092\ \mathrm{M}$$, what is the equilibrium concentration of $$\mathrm{NO}$$?

Accepted Answer

$$[NO] = \sqrt{K_c 	imes [N_2$][O_2$]} = 0.0142\ \mathrm{M}$$

Question 3

For the weak acid $$\mathrm{HCN}$$, with $$K_a = 4.9 	imes 10$$^{-10}$$ and an initial concentration of 0.15$$\ \mathrm{M}$$, what is the equilibrium concentration of $$\mathrm{H^+}$$?

Accepted Answer

$$[H^+] = \sqrt{K_a 	imes [HCN]_0} = 8.57 	imes 10$$^{-6}$$\ \mathrm{M}$$

Question 4

Which of the following best describes the solubility product constant ($$K_{sp}) $$for $$\mathrm{Mg(NH_4$)PO_4$}$$?

Accepted Answer

$$K_{sp} = [Mg$$^{2+}$$][NH_4$^+][PO_4$^{3-}]$$

Question 5

Write the dissolution equation and $$K_{sp}$$ expression for $$\mathrm{Ag_2CrO_4}.$$

Accepted Answer

Dissolution: $$\mathrm{Ag_2CrO_4(s) \rightleftharpoons 2Ag^+(aq) + $$CrO_4$$^{2-}(aq)}$$; $$K_{sp} = [Ag^+]^2[$$CrO_4$$^{2-}]$$

Question 6

The molar solubility of $$\mathrm{Ag_2SO_4} in $$pure water is $$1.2 	imes 10$$^{-5}$$\ \mathrm{M}. $$What is the value of $$K_{sp}$$?

Accepted Answer

$$K_{sp} = 4 	imes (1.2 	imes 10$$^{-5}$$)^3 = 6.9$$ 	imes $$10^{-15}$

Question 7

Which of the following statements about the effect of a common ion on solubility is correct?

Accepted Answer

The presence of a common ion decreases the solubility of an ionic compound.

Question 8

A buffer solution is prepared by mixing $$0.250\ \mathrm{mol} of $$formic acid ($$K_a = 1.8 	imes 10$$^{-4}$$) and 0.700$$\ \mathrm{mol}$$ of sodium formate in 1.00$$\ \mathrm{L}$$ of water. What is the pH of the buffer?

Accepted Answer

$$\mathrm{pH} = \mathrm{p}K_a + \log\left(\dfrac{[	ext{formate}]}{[	ext{formic acid}] }ight) = 4.74 + \log\left(\dfrac{0.700}{0.250}ight) = 5.18$$

Question 9

Which of the following is true about buffer capacity?

Accepted Answer

Buffer capacity increases as the concentrations of the buffer components increase.

Question 10

Which of the following is the correct $$K_{sp}$$ expression for $$\mathrm{Ca_3$(PO_4$)_2}$$?

Accepted Answer

$$K_{sp} = [Ca$$^{2+}$$]^3[PO_4$^{3-}]^2$$

Question 11

If $$K_{sp}$$ for $$\mathrm{$$PbCl_2$$} is$$ $$1.7 	imes 10$$^{-5}$$, what is the molar solubility of $$\mathrm{$$PbCl_2$$}$$ in pure water?

Accepted Answer

$$s = \sqrt{K_{sp}/4} = 2.06 	imes 10$$^{-2}$$\ \mathrm{M}$$

Question 12

Which of the following best describes the effect of temperature on the equilibrium constant $$K$$ for an endothermic reaction?

Accepted Answer

Increasing temperature increases $$K$$ for an endothermic reaction.

Question 13

Which of the following is the correct equilibrium expression for the reaction $$\mathrm{N_2O_4(g) \rightleftharpoons 2NO_2(g)}$$?

Accepted Answer

$$K_c = \dfrac{[NO_2$]^2}{[N_2O_4]}$$

Question 14

A solution is prepared by dissolving $$0.10\ \mathrm{mol} of$$ $$\mathrm{NH_4Cl} in$$ $$1.0\ \mathrm{L} of $$water. Which of the following best describes the resulting solution?

Accepted Answer

The solution will be acidic due to hydrolysis of $$\mathrm{NH_4$^+}.$$

Question 15

Which of the following is the correct relationship between $$K_a$$, $$K_b$$, and $$K_w$$ for a conjugate acid-base pair?

Accepted Answer

$$K_a 	imes K_b = K_w$$

Question 16

Which of the following is true about the pH of a buffer solution made from a weak acid and its conjugate base?

Accepted Answer

The pH is close to the $$pK_a of $$the acid when the concentrations of acid and base are equal.

Question 17

Which of the following is the correct dissolution equation for $$\mathrm{Ca(OH)_2}$$ and its $$K_{sp}$$ expression?

Accepted Answer

$$\mathrm{Ca(OH)_2(s) \rightleftharpoons Ca$$^{2+}$$(aq) + 2OH^-(aq)}$$; $$K_{sp} = [Ca$$^{2+}$$][OH^-]^2$$

Chemical Equilibrium and Solubility Product Constants: Study Notes

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