A 0.10 M solution of $NaHA$ is prepared, where $H X_{2} A$ has $p K_{a 1} = 3.0$ and $p K_{a 2} = 7.0$ (298 K). Use the standard amphiprotic approximation, $[H X^{+}] = K_{a 1} K_{a 2}$ . Select the correct statements.

Answer: A, B, C

[H X^{+}] = 1 0^{- 3} \times 1 0^{- 7} = 1 e - 05

M, so pH

= 5.0

and the solution is acidic. From

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

and

[H X^{+}]^{2} = K_{a 1} K_{a 2}

we get

[A X^{2 -}] = [H X_{2} A]

. D is wrong; amphiprotic does not mean neutral. Answer A, B, C.