Only litre buffer solution was prepared by adding 0.10 mol each of $\mathrm{NH}_3$ and $\mathrm{NH}_4 \mathrm{Cl}$ in deionised water. The change in pH on addition of 0.05 mol of HCl to the above solution is ________ $ imes 10^{-2}$, (Nearest integer) (Given : $\mathrm{pK}_{\mathrm{b}}$ of…

Question

Only litre buffer solution was prepared by adding 0.10 mol each of $\mathrm{NH}_3$ and $\mathrm{NH}_4 \mathrm{Cl}$ in deionised water. The change in pH on addition of 0.05 mol of HCl to the above solution is ________ $	imes 10^{-2}$, (Nearest integer) (Given : $\mathrm{pK}_{\mathrm{b}}$ of $\mathrm{NH}_3=4.745$ and $\log _{10} 3=0.477$)

Aicharya · Accepted Answer

$\begin{aligned}
& \mathrm{pOH}=\mathrm{pK}_{\mathrm{b}}+\log \frac{\left[\mathrm{NH}_4^{+}\right]}{\left[\mathrm{NH}_3\right]} \\
& \mathbf{p O H}=4.745
\end{aligned}$
on adding 0.05 mole HCl
$\begin{aligned}
& \begin{array}{llll}
\mathrm{NH}_3+ & \mathrm{H}^{\oplus} & \rightarrow & \mathrm{NH}_4^{\oplus} \\
0.1 & 0.05 & & 0.1 \\
0.05 & 0 & & 0.15
\end{array} \\
& \mathrm{pOH}^{\prime}=4.745+\log 3 \\
& \mathrm{pOH}^{\prime}-\mathrm{pOH}=0.477 \\
& 14-\mathrm{pH}^{\prime}-14+\mathrm{pH}=0.477 \\
& \Delta \mathrm{pH}=0.477 \\
& =47.7 \times 10^{-2} \approx 48 \times 10^{-2}
\end{aligned}$

Only litre buffer solution was prepared by adding 0.10 mol each of $\mathrm{NH}_3$ and $\mathrm{NH}_4…

Solution