Question

For the weak hypochlorous acid (HClO), which statement is true at the point halfway to the equivalence point?

Answer 1

The total amount of ClO- is equal to the Ka of the acid.


The total amount of HClO is equal to the pKa.


The total amount of H3O+ is equal to the amount of OH- .


The total amount of HClO is equal to ClO-.

Answer 2

\(\color{#0cbb34}{\text{Originally Posted by}}\) @Michael
Hypochlorous acid is a weak acid and dissociates:

\[HClO\rightleftharpoons H^++ OCl^-\]
\[K_a = \frac{[H^+][OCl^-]}{[HOCl]}\]

At half way to the equivalence point you can say that the number of moles of \[HOCl\] must be equal to the number of moles of \[OCl^-.\]This means the 4th response is the correct one. You can also see from the expression for Ka that these will cancel out so we can say Ka = [H+] and so pKa = pH. This is a good way to measure the pKa of a weak acid by constructing a pH curve during a titration and reading off the pH when the acid has been half neutralised.
\(\color{#0cbb34}{\text{End of Quote}}\)