Textbook Problem

Consider a salt of a weak base and a weak acid such as ammonium cyanide. Both the NH₄⁺ and CN⁻ ions interact with water in aqueous solution, but the net reaction can be considered as a proton transfer from NH₄⁺ to CN⁻.

NH₄⁺(aq) + CN⁻(aq) ⇌ NH₃(aq) + HCN(aq)

1. (a) Show that the equilibrium constant for this reaction, K_act, is
2. 1. $K_{\text{net}}=\frac{K_{\text{a}}{K}_{\text{b}}}{K_{\text{w}}}$

   where K_a is the ionization constant for the weak acid NH₄⁺ and K_b, is the constant for the weak base CN⁻.

3. (b) Calculate K_net values fur each of the following, NH₄CN, NH₄CH₃CO₂, and NH₄K Which salt has the largest value of K_act, and why?
4. (c) Predict whether a solution of each of the compounds in (b) is acidic or basic. Explain how you made this prediction (Yon do not need a calculation to make this prediction.)