Question

A litre of buffer solution contains $0.1$ mole of each of $N{H}_3$ and $N{H}_{4}CL$ On the addition of $0.02$ mole of $HCl$ by dissolving gaseous $HCl$, the $pH$ of the solution is found to be ____ $\times 10^{-3}$ (Nearest integer)
[Given : $p{K}_5\left(N{H}_3\right)=4.745$
$\log 2=0.301$
$\log 3=0.477$
$T=298K]$

Answer 1

Answer: 9079

In resultant solution
$n_{N{H}_3}=0.1-0.02=0.08$
$n_{N{H}_{4}Cl}=n_{N{H}_4^{+}}=0.1+0.02=0.12$
$pOH=p{K}_b+\log \frac{\left[N{H}_4^{+}\right]}{\left[N{H}_3\right]}$
$=4.745+\log \frac{0.12}{0.08}$
$=4.745+\log \frac{3}{2}$
$=4.745+0.477-0.301$
$pOH=4.921$
$pH=14-pH$
$=9.079$