Q: A solution is prepared by dissolving 0.10 mol of $\mathrm{NaF}$ in 1.0 L of water. If the $K_{sp}$ of $\mathrm{CaF_2}$ is $3.9 \times 10^{-11}$, what is the maximum concentration of $\mathrm{Ca^{2+}}$ that can be present before precipitation occurs?

$3.9 \times 10^{-9}\ \mathrm{M}$

Q: A saturated solution of $\mathrm{AgCl}$ is prepared. If $K_{sp} = 1.8 \times 10^{-10}$, what is the molar solubility of $\mathrm{AgCl}$ in pure water?

$1.3 \times 10^{-5}\ \mathrm{M}$

Question 1

A 0.10 M solution of acetic acid ($\mathrm{CH_3COOH}$, $K_a = 1.8 	imes 10^{-5}$) is prepared. What is the pH of this solution?

Accepted Answer

$\mathrm{pH} = 2.87$

Question 2

Which of the following best describes the common ion effect?

Accepted Answer

The suppression of the ionization of a weak acid or base by the addition of a strong electrolyte containing a common ion.

Question 3

A buffer is prepared by mixing 0.20 mol of ammonia ($\mathrm{NH_3}$) and 0.20 mol of ammonium chloride ($\mathrm{NH_4Cl}$) in enough water to make 1.0 L of solution. ($K_b$ for $\mathrm{NH_3} = 1.8 	imes 10^{-5}$). What is the pH of the buffer? ($pK_b = 4.74$)

Accepted Answer

$\mathrm{pH} = 9.25$

Question 4

Which equation is used to calculate the pH of a buffer solution?

Accepted Answer

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

Question 5

During a titration of a weak acid with a strong base, which of the following best describes the pH at the equivalence point?

Accepted Answer

The pH is greater than 7 because the conjugate base of the weak acid hydrolyzes to produce $\mathrm{OH}^-$.

Question 6

Which of the following statements about polyprotic acids is correct?

Accepted Answer

Each successive ionization has a smaller $K_a$ value than the previous one.

Question 7

A solution is prepared by dissolving 0.10 mol of $\mathrm{NaF}$ in 1.0 L of water. If the $K_{sp}$ of $\mathrm{CaF_2}$ is $3.9 	imes 10^{-11}$, what is the maximum concentration of $\mathrm{Ca^{2+}}$ that can be present before precipitation occurs?

Accepted Answer

$3.9 	imes 10^{-9}\ \mathrm{M}$

Question 8

Which of the following best explains why adding $\mathrm{HCl}$ to a solution of sodium acetate ($\mathrm{NaCH_3COO}$) decreases the pH?

Accepted Answer

The added $\mathrm{H^+}$ reacts with $\mathrm{CH_3COO^-}$ to form $\mathrm{CH_3COOH}$, reducing the concentration of base and increasing the concentration of acid.

Question 9

Which of the following is true regarding the buffer capacity of a solution?

Accepted Answer

Buffer capacity is greatest when the concentrations of acid and conjugate base are high and approximately equal.

Question 10

A saturated solution of $\mathrm{AgCl}$ is prepared. If $K_{sp} = 1.8 	imes 10^{-10}$, what is the molar solubility of $\mathrm{AgCl}$ in pure water?

Accepted Answer

$1.3 	imes 10^{-5}\ \mathrm{M}$

Question 11

Which of the following best describes what happens when $Q > K_{sp}$ for a slightly soluble salt?

Accepted Answer

A precipitate will form until $Q = K_{sp}$.

Question 12

During a titration of 25.0 mL of 0.100 M $\mathrm{HCl}$ with 0.100 M $\mathrm{NaOH}$, what is the pH after adding 30.0 mL of $\mathrm{NaOH}$?

Accepted Answer

$\mathrm{pH} = 12.70$

Question 13

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

Accepted Answer

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

Question 14

Which of the following best explains why the pH of a 0.10 M solution of $\mathrm{NaCl}$ is 7.00?

Accepted Answer

Neither $\mathrm{Na^+}$ nor $\mathrm{Cl^-}$ hydrolyze in water, so the solution remains neutral.

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

A buffer solution is made by mixing 0.50 mol of $\mathrm{H_2CO_3}$ and 0.25 mol of $\mathrm{NaHCO_3}$ in 1.0 L of water. If $pK_a = 6.35$, what is the pH of the buffer?

Accepted Answer

$\mathrm{pH} = 6.05$

Question 17

Which of the following best describes the purpose of a buffer in a biological system?

Accepted Answer

To maintain a relatively constant pH despite the addition of acids or bases.

Question 18

Which of the following is true about the effect of pH on the solubility of a salt containing a basic anion (e.g., $\mathrm{Mg(OH)_2}$)?

Accepted Answer

Lowering the pH increases the solubility because $\mathrm{H^+}$ reacts with the basic anion.

Question 19

Which of the following best describes the region of a titration curve where the buffer is most effective?

Accepted Answer

The region where $\mathrm{pH} \approx pK_a$.

Acid-Base Chemistry, Buffers, Titrations, and Solubility Equilibria: Study Notes

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