Which of the following mixtures (mixing equal volumes) will yield a final solution with a pH that is — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

An arithmetic average of pH requires specific logarithmic properties to align perfectly, which usually fails for direct mixture of $H^+$. However, mixing $HCl (pH=2, [H^+]=10^{-2})$ and $NaOH (pH=12, [OH^-]=10^{-2})$ in equal volumes results in exact neutralization, giving $pH=7$, which happens to be the average of 2 and 12. For WA/WB mixture where $K_a=K_b$, the resulting WA-WB salt hydrolyzes to $pH = 7 + \frac{1}{2}(pK_a - pK_b) = 7$, which is the average of 5 and 9. Strong acid/base mixtures do not average linearly.