Hydrolysis of salts Knowledge-Based Practice

Questions

1. 1.

   An aqueous solution of ammonium fluoride ($\text{NH}_4\text{F}$) at 25 °C is slightly acidic. Which of the following statements correctly explains why this solution is acidic rather than basic or neutral?

   • A) The fluoride ion hydrolyzes to a greater extent than the ammonium ion because $K_b(\text{F}^-) > K_a(\text{NH}_4^+)$.
   • B) Only the ammonium ion undergoes hydrolysis because fluoride is the conjugate base of a strong acid.
   • C) Hydrofluoric acid is a strong acid, preventing the fluoride ion from reacting with water molecules.
   • D) The acid dissociation constant of the ammonium ion is greater than the base dissociation constant of the fluoride ion ($K_a(\text{NH}_4^+) > K_b(\text{F}^-)$).
2. 2.

   When sodium hypochlorite ($\text{NaClO}$) dissolves in water, the hypochlorite ion undergoes hydrolysis according to the equation $\text{ClO}^-(aq) + \text{H}_2\text{O}(l) \rightleftharpoons \text{HClO}(aq) + \text{OH}^-(aq)$. Which expression correctly relates the equilibrium constant of this hydrolysis reaction ($K_\text{h}$) to the acid dissociation constant of hypochlorous acid ($K_\text{a}$) and the ion-product constant of water ($K_\text{w}$)?

   • A) $K_\text{h} = K_\text{a} \cdot K_\text{w}$
   • B) $K_\text{h} = \frac{K_\text{a}}{K_\text{w}}$
   • C) $K_\text{h} = \frac{1}{K_\text{a} \cdot K_\text{w}}$
   • D) $K_\text{h} = \frac{K_\text{w}}{K_\text{a}}$
3. 3.

   Which of the following salts undergoes hydrolysis of both its cation and its anion when dissolved in water?

   • A) $\text{NH}_4\text{NO}_2$
   • B) $\text{NaNO}_2$
   • C) $\text{NH}_4\text{NO}_3$
   • D) $\text{KNO}_3$
4. 4.

   Which of the following net ionic equations correctly represents the hydrolysis reaction that occurs when potassium cyanide ($\text{KCN}$) is dissolved in water?

   • A) $\text{K}^+(aq) + \text{H}_2\text{O}(l) \rightleftharpoons \text{KOH}(aq) + \text{H}^+(aq)$
   • B) $\text{CN}^-(aq) + \text{H}_3\text{O}^+(aq) \rightleftharpoons \text{HCN}(aq) + \text{H}_2\text{O}(l)$
   • C) $\text{KCN}(s) + \text{H}_2\text{O}(l) \rightleftharpoons \text{K}^+(aq) + \text{CN}^-(aq)$
   • D) $\text{CN}^-(aq) + \text{H}_2\text{O}(l) \rightleftharpoons \text{HCN}(aq) + \text{OH}^-(aq)$
5. 5.

   Which of the following salts produces an acidic solution with a pH less than 7 at 25 °C due to cation hydrolysis?

   • A) $NH_4Cl$
   • B) $KCN$
   • C) $NaCl$
   • D) $CH_3COOK$

Answers and step-by-step solutions appear after you finish the test.