The ionisation constant of an acid, $K_a$ is the measure of strength of an acid. The $K_a$ values of

Question

The ionisation constant of an acid, $K_a$ is the measure of strength of an acid. The $K_a$ values of acetic acid, hypochlorous acid and formic acid are $1.74 	imes 10^{-5}$, $3.0 	imes 10^{-8}$ and $1.8 	imes 10^{-4}$ respectively. Which of the following orders of pH of $0.1 \mathrm{~mol} \mathrm{dm}^{-3}$ solutions of these acids is correct?

Professor PC Thomas Classes · Answer

(b) : $K_a$ is a measure of the strength of the acid i.e., larger the value of $K_a$, the stronger is the acid. Thus, the correct order of acidic strength is \  Stronger the acid, lesser will be the value of pH . Hence, the correct order of pH is $\mathrm{HClO}>\mathrm{CH}_3 \mathrm{COOH}>\mathrm{HCOOH}$.