Q: A solution contains $0.010$ M $\mathrm{Ca^{2+}}$ ions. What is the molar solubility of $\mathrm{CaF_2}$ in this solution? ($K_{sp} = 3.9 \times 10^{-11}$)

$3.9 \times 10^{-11} = (0.010)(2s)^2 \Rightarrow s = 3.1 \times 10^{-5}$ M

Question 1

Which statement best describes the common-ion effect in a solution containing acetic acid and sodium acetate?

Accepted Answer

The presence of acetate ion from sodium acetate suppresses the ionization of acetic acid, shifting equilibrium to the left.

Question 2

A buffer solution is prepared by mixing 0.20 mol of a weak acid (HA) and 0.20 mol of its conjugate base (A-) in 1.0 L of water. If the $K_a$ of HA is $2.0 	imes 10^{-5}$, what is the pH of the buffer?

Accepted Answer

$\mathrm{pH} = \mathrm{p}K_a + \log\left(\frac{[A^-]}{[HA]}\right) = 4.70 + \log(1) = 4.70$

Question 3

Which of the following will increase the solubility of calcium fluoride ($\mathrm{CaF}_2$) in water?

Accepted Answer

Lowering the pH by adding a strong acid.

Question 4

During the titration of a weak acid with a strong base, what is true at the halfway point to the equivalence point?

Accepted Answer

The pH equals the $\mathrm{p}K_a$ of the acid.

Question 5

A buffer is made by adding 0.300 mol $\mathrm{CH_3COOH}$ and 0.300 mol $\mathrm{CH_3COO^-}$ to 1.00 L of water. If 0.020 mol NaOH is added, what is the new pH? ($K_a = 1.8 	imes 10^{-5}$)

Accepted Answer

$\mathrm{pH} = 4.74 + \log\left(\frac{0.320}{0.280}\right) = 4.80$

Question 6

Which of the following best explains why buffers resist drastic changes in pH upon addition of small amounts of acid or base?

Accepted Answer

Buffers contain a weak acid and its conjugate base, which react with added acid or base to minimize pH change.

Question 7

Which equation is the Henderson-Hasselbalch equation for a buffer made from a weak acid and its conjugate base?

Accepted Answer

$\mathrm{pH} = \mathrm{p}K_a + \log\left(\frac{[A^-]}{[HA]}\right)$

Question 8

Which of the following statements about the solubility-product constant ($K_{sp}$) is correct?

Accepted Answer

$K_{sp}$ is used to calculate the equilibrium concentrations of ions in a saturated solution.

Question 9

A solution contains $0.010$ M $\mathrm{Ca^{2+}}$ ions. What is the molar solubility of $\mathrm{CaF_2}$ in this solution? ($K_{sp} = 3.9 	imes 10^{-11}$)

Accepted Answer

$3.9 	imes 10^{-11} = (0.010)(2s)^2 \Rightarrow s = 3.1 	imes 10^{-5}$ M

Question 10

Which of the following is true about the pH at the equivalence point during the titration of a weak acid with a strong base?

Accepted Answer

The pH is greater than 7.00.

Question 11

Which of the following will NOT form a buffer solution?

Accepted Answer

A mixture of $\mathrm{HCl}$ and $\mathrm{NaCl}$

Question 12

Which of the following best describes the effect of adding a common ion to a saturated solution of a sparingly soluble salt?

Accepted Answer

The solubility of the salt decreases.

Question 13

Which of the following is a correct application of Le Chatelier's principle to the common-ion effect?

Accepted Answer

Adding a common ion shifts the equilibrium toward the reactants, reducing ionization.

Question 14

Which of the following is true about the buffer capacity?

Accepted Answer

Buffer capacity increases as the concentrations of acid and base increase.

Question 15

Which of the following is a correct statement about the use of acid-base indicators in titrations?

Accepted Answer

Indicators can be used to determine the equivalence point if their color change occurs near the rapid pH change region.

Question 16

Which of the following is true about the solubility of salts containing anions that are conjugate bases of weak acids?

Accepted Answer

Their solubility increases in acidic solution.

Question 17

Which of the following best describes the effect of complex ion formation on the solubility of a salt?

Accepted Answer

Complex ion formation increases the solubility of the salt.

Question 18

If $Q > K_{sp}$ for a solution containing a sparingly soluble salt, what will happen?

Accepted Answer

A precipitate will form until equilibrium is reached.

Question 19

Which of the following metals forms amphoteric hydroxides that are soluble in both strong acids and bases?

Accepted Answer

Zn

Chapter 17: Aqueous Equilibria: Buffers, Titrations, and Solubility

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