Question

The pH of 0.1M solution of cyanic acid (HCNO) is 2.34. Calculate the ionization constant of the acid and its degree of ionization in the solution.

Answer 1

$c=0.1MpH=2.34-log\left[H^{+}\right]=pH-log\left[H^{+}\right]=2.34\left[H^{+}\right]=4.5\times {10}^{-3}$
Also,
$\left[H^{+}\right]=c\alpha 4.5\times {10}^{-3}=0.1\times \alpha \frac{4.5\times {10}^{-3}}{0.1}=\alpha \alpha =45\times {10}^{-3}=.045$
Then,
$K_a=c{\alpha }^2=0.1\times (45\times {10}^{-3}{)}^2=202.5\times {10}^{-6}=2.02\times {10}^{-4}$