Calculate `[H^+],[HCOO^(-)] and [OCN^(-)]` in a solution that contains 0.1 M HCOOH `(K_a=2.4xx10^(-4)) and 0.1 M HOCN (K_a=4xx10^(-4))`.

Options

A. `[H^+]=8xx10^(-3)M`
B. `[HCOO^(-)]=3xx10^(-3)M`
C. `[OCN^(-)]=5xx10^(-3)M`
D. All of these

Answer

D

Explanation

`[H^+]=sqrt((0.1xx2.4xx10^(-4))+(0.1xx4xx10^(-4)))=8xx10^(-3)M`
for HCOOH, `Ka=2.4xx10^(-4)=([H^+][HCOO^(-)])/([HCOOH])`
`:. [HCOO^(-)]=3xx10^(-3) M`
for HOCN, `Ka=4xx10^(-4)=([H^+][OCN^(-)])/([HOCN])`
`:. [OCN^(-)]=5xx10^(-3) M`