MCQ
$NH_4CN$ is a salt of weak acid $HCN (K_a = 6.2 \times 10^{-10})$ and a weak base $NH_4OH (K_b = 1.8 \times 10^{-5})$. A one molar solution of $NH_4CN$ will be:
  • A
    neutral
  • B
    strongly acidic
  • C
    strongly basic
  • weakly basic

Answer

Correct option: D.
weakly basic
d
${\text{pH}} = 7 + \frac{{{\text{p}}{{\text{K}}_{\text{a}}}}}{2} - \frac{{{\text{p}}{{\text{K}}_{\text{b}}}}}{2}$

$ = 7 - \frac{{4.74}}{2} + \frac{{9.20}}{2}$

$ = 7 - 2.37 + 4.6$

$ = 9.23{\text{ weakly basic}}$

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