$100 mL$ of $0.10 M$ $NaHCO X_{3}$ is mixed with $100 mL$ of $0.10 M$ $NaOH$ . For carbonic acid $p K_{a 1} = 6.35$ and $p K_{a 2} = 10.33$ . Neglect the second hydrolysis step of the carbonate formed. The pH of the resulting solution is

Answer: C

HCO X_{3} X^{-} + OH X^{-} CO X_{3} X^{2 -} + H X_{2} O

is complete and gives

0.010 mol

CO X_{3} X^{2 -}

200 mL

, i.e.

0.050 M

. Carbonate hydrolyses with

K_{h} = K_{w} / K_{a 2}

, so

pH = 7 + \frac{1}{2} (p K_{a 2} + lo g C) = 7 + \frac{1}{2} (10.33 - 1.301) = 11.51