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

B

Explanation

`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 correct order of acidic strength is
`{:(,HCOOH,gt,CH_(3)COOH,gt,HClO),(K_(a):,1.8xx10^(-4),,1.74xx10^(-5),,3.0xx10^(-8)):}`
Stronger the acid, lesser will be the value of pH. Hence, the correct order of pH is `HClOgtCH_(3)COOHgtHCOOH`