Question

Calculate the ratio of `[HXOO^(-)]` and `[F^(-)]` in a mixture of 0.2 M HCOOH `(K_(a)=2xx10^(-4))` and 0.1 M HF `(K_(a)=6.6xx10^(-4)) :`
A. `1 : 6.6`
B. `1: 3.3`
C. `2:3.3`
D. `3.3:2`

Answer 1

Correct Answer - C
`underset(C_(1)-x)(HCOOH_((aq))) + underset(x)(H_(2)O_((l))) hArr HCOO_((aq))^(-)+H_(3)O_((aq))^(+)`
`:. alpha` is very less for boh air acid so
`K_(a)(HF) = (y(x+y))/(C_(2))`
`:. (x)/(y) = (K_(a)(HCOOH))/(K_(a)(HF)C_(2))`
`([HCOO^(-)])/([F^(-)]) = x/y`
`= (2 xx 10^(-4) xx 0.2)/(6.6 xx 10^(-4) xx 0.1) = 2/(3.3)`