What is `[H^(+)]` in `mol//L` of a solution that is `0.20 M` in `CH_(3)COONa` and `0.1 M` in `CH_(3)COOH`? `K_(a)` for `CH_(3)COOH` is `1.8xx10^(-5)`?

Options

A. `3.5 xx 10^(-7)`
B. `1.1 xx 10^(-5)`
C. `4.0 xx 10^(-6)`
D. `9.0 xx 10^(-6)`

Answer

D

Explanation

`underset((c-x))(CH_(3)COOH) hArr underset(X)(CH_(3)COO^(-)) +underset(X)(H^(+))`
`underset(0.2 M)(CH_(3)COONa) to underset(0.2 M)(CH_(3)COO^(-)) +underset(0.2M)(Na^(+))`
`(CH_(3)COO^(-)) =0.2 + x ~~ 0.2 M`
`[CH_(3)COO^(-)] =0.2 + x ~~ 0.2 M`
`K_(a) = [[CH_(3)COO^(-)][H^(+)]]/[[CH_(3)COOH]]`
`H^(+) = (ka[CH_(3)COOH^(-)]]/[[CH_(3)COO^(-)]]`
`H^(+) =((1.8xx 10^(-5))xx(0.1M))/((0.2 M))=9.0 xx 10^(-6)`