A saturated solution of H2S ([H2S] = 0.10 M) is buffered at pH = 3.0. Given K_a1K_a2 = 1.0x10^-21, the concentration of S^2- is

JEE Main levelSingle correct optionDifficulty 2 of 3ia178

A saturated solution of $H X_{2} S$ ( $[H X_{2} S] = 0.10 M$ ) is buffered at $pH = 3.0$ . Given $K_{a 1} K_{a 2} = 1.0 \times 1 0^{- 21}$ , the concentration of $S X^{2 -}$ is

From

K_{a 1} K_{a 2} = [H X^{+}] X^{2} [S X^{2 -}] / [H X_{2} S]

[S X^{2 -}] = 1 0^{- 21} \times 0.10/ (1 0^{- 3})^{2} = 1.0 \times 1 0^{- 16} M