`H_2A ` is a weak diptotic acid . IF the pH of 0.1 M ` H_2A ` solution is 3 and concentration of `A^(2) is 10 ^(-12) " at " 25 ^(@) C ` Select correct statement (s)

Options

A. `[H^(+) ]_("total") ~~[H^(+) ]` from first step ionization of acid `H_2A `
B. Concentration of `OH^(-) ` in solution is `10 ^(-3) ` M
C. The value of `K_(a_1) ` is nearly `10 ^(5)`
D. ` p^(ka_2) - p^(ka_1) =9`

Answer

A, C

Explanation

` [H^(+) ]=sqrt(K_(a_1) xx C ) rArr 10^(-3) =sqrt( K_(a_1)xx 10^(-1)) `
` K_(a_1) =10 ^(-5) rArr [A^(-2) ]=K_(a_2) rArr P^(K_(a2 )) = 12 `
` P^(K_(a2)) -P^(K_(a3)) = 7 `