A certain mixture of `HCl` and `CH_(3)-COOH` is `0.1 M` in each of the acids. `20 ml` of this solution is titrated against `0.1 M NaOH`. By how many units does the `pH` change from the start to the stage when the `HCl` is almost completely neutralized and acidic acid remains unreacted? `K_(a)` for acetic acid `=2xx10^(-5)`.

Answer

2.03

Explanation

Initial `[H^(+)]=0.1` [from weak acid `H^(+)` can be neglected]
After neutralization of HCl , Volume would double.
Hence `[CH_(3)COOH]=(0.1xx20)/40 =0.05`
`[H^(+)]=sqrt(K_(a).C)`
`[H^(+)]=9.48xx10^(-4)`
`pH=3.03`
`DeltapH=(3.03-1)=2.03`