MCQ
The $pK_b$ of $C{N^\Theta }$ is $4.7.$ The $pH$ of solution prepared by mixing $2.5\,mol$ of $KCN$ and $2.5\,mol$ of $HCN$ in water and making the total volume upto $500\,mL$ is.
  • A
    $10.3$
  • $9.3$
  • C
    $8.3$
  • D
    $4.7$

Answer

Correct option: B.
$9.3$
b
It forms basic buffer

$\mathrm{pOH}=\mathrm{pK}_{\mathrm{b}}+\log \left(\frac{2.5 / 500}{2.5 / 500}\right)=4.7$

$\mathrm{pH}=14-4.7=9.3$

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