The pH of 0.01 M solution of acetic acid is 5.0. What are the values of `[H^(+)] and K_(a)` respectively?

Options

A. `1 xx 10^(-5) M, 1 xx 10^(-8)`
B. `1 xx 10^(-5) M, 1 xx 10^(-9)`
C. `1 xx 10^(-4) M, 1 xx 10^(-8)`
D. `1 xx 10^(-3) M, 1 xx 10^(-8)`

Answer

A

Explanation

pH of 0.01 M solution of acetic acid = 5
`pH = -"log"[H^(+)]`
`implies -"log"10^(-5) = -"log"[H^(+)]( :' -"log" 10^(-5) = 5)`
`implies [H^(+)] = 10^(-5)M`
In weak acids, `[H^(+)] = sqrt(K_(a).C)`
`K_(a) = [H^(+)]^(2)/C = (10^(-5))^(2)/0.01 = 1 xx 10^(-10)/10^(-2) = 1 xx 10^(-8)`