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. `9.0 xx 10^(-6)`
B. `3.5 xx 10^(-4)`
C. `1.1 xx 10^(-5)`
D. `1.8 xx 10^(-15)`

Answer

A

Explanation

The given solution is an acidi buffer. Hence
`pH =pK_(a)+log.(["Salt"])/(["Acid"])`
`=-log (1.8 xx 10^(-5))+log. (0.20)/(0.10)`
or ` -log [H^(+)]=log .(2)/(1.8 xx 10^(-5))`
or `log|(1)/(H^(+))|=log. (2)/(1.8 xx 10^(-5))`
or `|H^(+)|=(1.8 xx 10^(-5))/(2)=0.9 xx 10^(-5)M`