When CuSO_4 reacts with KCN it forms CuCN , which is insoluble in water. It is soluble in excess of KCN due to the formation of the following complex:

Correct answer: B. K_3[Cu(CN)_4] CuSO_4 reacts with KCN to give a white precipitate of cuprous cyanide and cyanogen gas. The cuprous cyanide dissolves in excess of KCN forming K_3 [Cu(CN)_4] gathered CuSO_4+2 KCN arrow K_2 SO_4+ Cu(CN)_2 2 Cu(CN)_2 arrow 2 CuCN+CN-CN CuCN+3 KCN arrow K_3[Cu(CN)_4] gathered

NEET 2002

Exam: NEET
Year: 2002
Subject: Chemistry
Chapter: d and f Block Elements

NEET 2002 · Chemistry · d and f Block Elements

When CuSO_4 reacts with KCN it forms CuCN , which is insoluble in...

When

\mathrm{CuSO}_4

reacts with

\mathrm{KCN}

it forms

\mathrm{CuCN}

, which is insoluble in water. It is soluble in excess of

\mathrm{KCN}

due to the formation of the following complex:

Options

A $\mathrm{K}_2\left[\mathrm{Cu}(\mathrm{CN})_4\right]$
B $\mathrm{K}_3\left[\mathrm{Cu}(\mathrm{CN})_4\right]$
C $\mathrm{CuCN}_2$
D $\mathrm{Cu}\left[\mathrm{KCu}(\mathrm{CN})_4\right]$

Correct answer

B. $\mathrm{K}_3\left[\mathrm{Cu}(\mathrm{CN})_4\right]$

Step-by-step solution

\mathrm{CuSO}_4

reacts with

\mathrm{KCN}

to give a white precipitate of cuprous cyanide and cyanogen gas. The cuprous cyanide dissolves in excess of

\mathrm{KCN}

forming

\mathrm{K}_3

\left[\mathrm{Cu}(\mathrm{CN})_4\right]

\begin{gathered} \mathrm{CuSO}_4+2 \mathrm{KCN} \rightarrow \mathrm{K}_2 \mathrm{SO}_4+ \mathrm{Cu}(\mathrm{CN})_2 \\ 2 \mathrm{Cu}(\mathrm{CN})_2 \rightarrow 2 \mathrm{CuCN}+\mathrm{CN}-\mathrm{CN} \\ \mathrm{CuCN}+3 \mathrm{KCN} \rightarrow \mathrm{K}_3\left[\mathrm{Cu}(\mathrm{CN})_4\right] \end{gathered}

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