The acid ionization constant of Zn is . What is the pH of 0.001 M solution of ZnCl? () — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

Zn$^{2+}$ undergoes cationic hydrolysis acting as a weak acid: $\text{Zn}^{2+} + \text{H}_2\text{O} \rightleftharpoons \text{Zn(OH)}^+ + \text{H}^+$. With $K_a = 2.0 \times 10^{-10}$ and $C = 10^{-3}\text{ M}$, the hydrogen ion concentration is $[\text{H}^+] = \sqrt{K_a C} = \sqrt{2.0 \times 10^{-10} \times 10^{-3}} = \sqrt{2 \times 10^{-13}} = \sqrt{0.2 \times 10^{-12}} \approx 4.47 \times 10^{-7}\text{ M}$. The $\text{pH} = -\log(4.47 \times 10^{-7}) = 7 - \log(4.47) \approx 7 - 0.65 = 6.35$.