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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