Question

$K_{a_1}$, $K_{a_2}$ and $K_{a_3}$ are the respective ionisation constants for the following reactions.
$H_2S \rightleftharpoons H^+ + HS^-$
$HS^- \rightleftharpoons H^+ + S^{2-}$
$H_2S \rightleftharpoons 2H^+ + S^{2-}$
The correct relationship between $K_{a_1}$, $K_{a_2}$ and $K_{a_3}$ is
(a) $K_{a_3}$ = $K_{a_1}$ x $K_{a_2}$
(b) $K_{a_3}$ = $K_{a_1}$ + $K_{a_2}$
(c) $K_{a_3}$ = $K_{a_1}$ - $K_{a_2}$
(d) $K_{a_3}$ = $K_{a_1}$ / $K_{a_2}$

Answer 1

(b) $K_{a_3}$ = $K_{a_1}$ + $K_{a_2}$

Answer 2

K

a

3

= K_{a_1}K

a

1

+ K_{a_2}K

a

2