Ionisation constant for acids HA and `BH^(+)` are `10^(-7)` and `10^(-3)` respectively. Find the `pK_(eq.)` for the reaction, `HA+BhArrBH^(+)+A^(-)`.

Answer

4

Explanation

`K_(a_(HA))=([H^(+)][A^(-)])/([HA])=10^(-7) …..(1)`
`K_(a_(BH^(+)))=([B][H^(+)])/([BH^(+)])=10^(-3) …..`(2)
`:. K_((eq.))=(K_(a_(HA)))/(K_(a_(BH^(+))))=([A^(-)][BH^(+)])/([HA][B])`
`=(10^(-7))/(10^(-3))=10^(-4)`
or `-log K_((eq.))=pK_((eq.))=4`