If a aqueous solution of a weak acid is diluted to at a constant temperature, which of the following — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

Dilution increases the degree of ionization ($\alpha \propto 1/\sqrt{C}$). $K_a$ is an equilibrium constant and depends only on temperature, so it remains unchanged. $[H^+] = \sqrt{K_a C}$; when $C$ drops by a factor of 100, $[H^+]$ drops by a factor of $\sqrt{100} = 10$, meaning it does not decrease by 100. A decrease in $[H^+]$ by a factor of 10 translates to an increase in pH by $\log(10) = 1$ unit.