Question

It has been found that the `pH` of a `0.01 M` solution of an organic acid is `4.15`. Calculate the concentration of the anion, the ionization constant of the acid and its `pK_(a)`.

Answer 1

`pH =- log [H^(+)] " or " log [H^(+)] =- pH =- 4.15 = bar(5).85`
`[H^(+)] = " Antilog " (bar(5).85) =7.08 xx 10^(-5)M`
`[A^(-)] = [H^(+)] =7.08 xx 10^(-5)M`
`[K_(a)] =[[H^(+)][A^(-)]]/[[HA]] = ((7.08 xx 10^(-5))xx (7.08 xx 10^(-5)))/((0.01)) =5.0 xx 10^(-7)`
`pK_(a) =- log K_(a)=- log (5.0 xx 10^(-7))= (7-log 5) =(7-0.699) =6.301`