Question

Calculate the $pH$ (nearest integer) of $0.010M$ $NaH{CO}_3$ solution. $K_1=4.5\times {10}^{-7}$ and $K_2=4.7\times {10}^{-11}$ for carbonic acid.

Answer 1

In the calculation of pH $K_1$ will be used because the pH is asked for $NaHC{O}_3$
$\underset{\text{carbonic acid}}{H_{2}C{O}_3}\to H^{+}+HC{O}_3^{-};K_1$
$\underset{\text{bicarbonic acid}}{HC{O}_3^{-}}\to H^{+}+C{O}_3^{2-};K_2$

$K_1$ value used in the calculation

Now,

$pH=\frac{pKw+pK{a}_1+logC}{2}=\frac{14+6.35+2}{2}=11.2\approx 11$