The pH of acetic acid solution in water, considering the simultaneous dimerization of acid is — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

As calculated previously, the concentration of the monomer in water remains approximately $0.1\text{ M}$ (since dimerization is negligible). The acid dissociates with $K_a = 2.0 \times 10^{-5}$. Thus, $[\text{H}^+] = \sqrt{K_a \cdot C} = \sqrt{2.0 \times 10^{-5} \times 0.1} = \sqrt{2.0 \times 10^{-6}} = 1.414 \times 10^{-3}\text{ M}$. The pH is $-\log(1.414 \times 10^{-3}) = 3 - \log(1.414) \approx 3 - 0.15 = 2.85$. Therefore, correct answer is B.