A solution containing \(\ce{HCl}\) and the weak acid \(\ce{HClO2}\) has a pH of 2.4. Enough \(\ce{KOH(aq)}\) is added to the solution to increase the pH to 10.5. The amount of which of the following species increases as the \(\ce{KOH(aq)}\) is added?

Summary Submit Skip Question

The strong base and acid will react and neutralize first:

$$ \ce{KOH(aq) + HCl(aq) -> H2O(l) + K+(aq) + Cl-(aq)} $$

Since the solution becomes alkaline, we can infer that more strong base is added. The base would react with \(\ce{HClO2}\):

$$ \ce{KOH(aq) + HClO2(aq) -> H2O(l) + K+(aq) + ClO2-(aq) } $$

Note that there are two reasonable options that increase in solution: \(\ce{Cl-(aq)}\) and \(\ce{ClO2-(aq)}\). However, since we know that \(\ce{HCl}\) is a stronger acid than \(\ce{HClO2}\), the \(\ce{Cl-}\) ions were already present in solution throughout the process. On the other hand, most of the \(\ce{ClO2-(aq)}\) ions did not dissociate from the weak acid at the start of the reactions. It is only after the strong base liberates the proton do \(\ce{ClO2-(aq)}\) ions noticeably increase.