The ionisation cosntabnt of an acid, `K_(a)` is the meaure of strength of an acid. The `K_(a)` values of acetic acid, hypochlorous acid and formic acid are `1.74xx10^(-5)`, `3.0xx10^(-8)` and `1.8xx10^(-4)` respectively. Which of the following orders of ph of `0.1` mol `dm^(-3)` solutions of these acids is correct ?

Options

A. acetic acid gt hypochlorous acid gt formic acid
B. hypochlorous acid gt acetic acid gt formic acid
C. formic acid gt hypochlorous acid gt acetic acid
D. formic acid gt acetic acid gt hypochlorous acid

Answer

D

Explanation

`[H_3O^+]=sqrt(K_a.C)` For the same concentration,
`[H_3O^+] prop sqrtK_a` . But pH =-log `[H_3O^+]`
Larger the value of `K_a` , larger will be `[H_3O^+]` and lower will be pH .