A buffer solution is prepared by mixing $0.1 \mathrm{M} \mathrm{HCN}$ and $0.2 \mathrm{M} \mathrm{NaCN}$…

A buffer solution is prepared by mixing $0.1 \mathrm{M} \mathrm{HCN}$ and $0.2 \mathrm{M} \mathrm{NaCN}$ What is the $\mathrm{pH}$ of buffer solution if $\mathrm{pKa}$ of $\mathrm{HCN}$ is 9.3? $(\log 2=0.3010)$
  1. 4.2
  2. 2.0
  3. 9.60
  4. 6.15

Solution

$\begin{aligned} & \mathrm{pH}=\mathrm{pKa}+\log \frac{[\text { Salt }]}{[\text { Acid }]} \\ & =9.3+\log \frac{(0.2)}{(0.1)} \\ & =9.3+0.3010 \\ & =9.60\end{aligned}$

Asked in: MHT CET 2022 (08 Aug Shift 2)

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