Q83 / 200 · NEET 2006 · Chemistry

Copper sulphate dissolves in excess of $\mathrm{KCN}$ to give:

  • A
    $\mathrm{Cu}(\mathrm{CN})_2$
  • B
    $\mathrm{CuCN}$
  • Correct answer
    C
    $[\mathrm{Cu}(\mathrm{CN}) 4]^{3-}$
  • D
    $\left[\mathrm{Cu}(\mathrm{CN})_4\right]^{2-}$

Solution

$\mathrm{CuSO}_4+2 \mathrm{KCN} \rightarrow \mathrm{Cu}(\mathrm{CN})_2+\mathrm{K}_2 \mathrm{SO}_4$ Cupric cyanide $$ \begin{array}{r} 2 \mathrm{Cu}(\mathrm{CN})_2 \rightarrow 2 \mathrm{Cu}(\mathrm{CN})+\mathrm{NC}-\mathrm{CN} \\ \text { Cyanogen } \\ \mathrm{Cu}(\mathrm{CN})+3 \mathrm{KCN} \rightarrow \mathrm{K}_3\left[\mathrm{Cu}(\mathrm{CN})_4\right] \end{array} $$ Soluble complex salt

Hence, the correct answer is option: 'C'.

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