Question 1

Which of the following best describes a conjugate acid-base pair according to the Brønsted-Lowry definition?

Accepted Answer

Two species that differ by a single proton.

Question 2

What is the effect called when the addition of a common ion suppresses the ionization of a weak electrolyte in solution?

Accepted Answer

Common-ion effect

Question 3

A buffer solution is prepared by mixing 0.20 M CH$_3$COOH and 0.10 M CH$_3$COO$^-$ in water. Which equation would you use to calculate the pH of this buffer?

Accepted Answer

$\mathrm{pH} = \mathrm{p}K_a + \log \left( \dfrac{[\mathrm{CH}_3\mathrm{COO}^-]}{[\mathrm{CH}_3\mathrm{COOH}]} \right)$

Question 4

Which of the following statements about buffer solutions is TRUE?

Accepted Answer

A buffer solution resists changes in pH when small amounts of acid or base are added.

Question 5

If you add NaCH$_3$COO to a solution of CH$_3$COOH, what happens to the ionization of acetic acid?

Accepted Answer

Ionization of acetic acid is suppressed due to the common-ion effect.

Question 6

A buffer is made by mixing 0.15 M hydrocyanic acid (HCN) and 0.36 M sodium cyanide (NaCN). The $K_a$ for HCN is $4.9 	imes 10^{-10}$. What is the pH of the buffer? (Use $\mathrm{pH} = \mathrm{p}K_a + \log \left( \dfrac{[\mathrm{CN}^-]}{[\mathrm{HCN}]} ight)$)

Accepted Answer

pH = 9.38

Question 7

Which of the following is the correct expression for the solubility product constant ($K_{sp}$) of calcium hydroxide, Ca(OH)$_2$?

Accepted Answer

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

Question 8

A solution is prepared by adding 25.00 mL of 0.1500 M HNO$_3$ to 30.00 mL of 0.1000 M NaOH. After the reaction, what is the pH of the solution? (Assume complete neutralization and dilution.)

Accepted Answer

pH = 1.87

Question 9

Which of the following compounds is LEAST likely to form a buffer solution when mixed with its salt?

Accepted Answer

HCl and NaCl

Question 10

What is the molar solubility of PbCl$_2$ in pure water if $K_{sp} = 1.17 	imes 10^{-5}$? (Let $s$ be the molar solubility.)

Accepted Answer

$s = \sqrt{K_{sp}/(4)}$ where $K_{sp} = 4s^3$, so $s = \sqrt[3]{K_{sp}/4}$

Question 11

Which of the following best explains why buffer solutions are important in biological systems?

Accepted Answer

They maintain a relatively constant pH, which is crucial for enzyme activity.

Question 12

Which of the following is the correct $K_{sp}$ expression for silver chloride, AgCl?

Accepted Answer

$K_{sp} = [\mathrm{Ag}^+] [\mathrm{Cl}^-]$

Question 13

A buffer solution is made by mixing 500 mL of 0.15 M CH$_3$COOH and 200 mL of 0.25 M NaCH$_3$COO. What is the first step in calculating the pH of the buffer?

Accepted Answer

Calculate the diluted concentrations of CH$_3$COOH and NaCH$_3$COO.

Question 14

Which of the following is TRUE about the pH of acidic and basic buffer solutions compared to their original acid or base alone?

Accepted Answer

Acidic buffers have a higher pH than the original acid alone; basic buffers have a lower pH than the original base alone.

Question 15

Which of the following is NOT a characteristic of buffer solutions?

Accepted Answer

Buffers are made from strong acids and strong bases.

Question 16

Which equation would you use to calculate the hydroxide ion concentration in a basic buffer solution?

Accepted Answer

$[\mathrm{OH}^-] = K_b 	imes \dfrac{[	ext{base}]}{[	ext{conjugate acid}]}$

Question 17

Which of the following is the correct dissociation reaction for Zn$_3$(PO$_4$)$_2$ in water?

Accepted Answer

Zn$_3$(PO$_4$)$_2$ (s) $\rightarrow$ 3 Zn$^{2+}$ (aq) + 2 PO$_4^{3-}$ (aq)

Question 18

Which of the following would increase the solubility of BaSO$_4$ in water?

Accepted Answer

Removing Ba$^{2+}$ ions from the solution.

Aqueous Ionic Equilibrium: Conjugate Acids/Bases, Buffers, and Solubility

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