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. `1.8xx10^(-5)`
B. `9.0xx10^(-6)`
C. `3.5xx10^(-4)`
D. `1.1xx10^(-5)`

Answer

B

Explanation

`{:(CH_3COOHhArr , CH_3COO^(-)+, H^+),(1-x,x,x),(CH_3COONa to , CH_3COO^(-)+ , Na^+),(0.2,0.2M,0.2M):}`
`K_a=([CH_3COO^-][H^+])/([CH_3COOH])`
`[CH_3COOH]` =1-x `approx` 0.1 M (`because` x is very small)
`[CH_3COO^-]`=0.2 + x `approx` 0.2 M
`therefore [H^+]=K_a ([CH_3COOH])/([CH_3COO^-])=(1.8xx10^(-5)xx0.1)/0.2`
`[H^+]=9.0xx10^(-6)`