Question

$CuSO_4$ decolourises on addition of $KCN$, the product is

• A. $[Cu (CN)_4]^{2-}$
• B. $Cu^{2+}$ gets reduced to form $[Cu(CN)_4]^{3-}$
• C. $Cu (CN)_2$
• D. $CuCN$

Answer 1

Answer: (B)

$ [CuSO_4 + 2KCN \rightarrow Cu(CN)_2 + K_2SO_4] \times 2$
$2Cu (CN)_2 \rightarrow Cu_2(CN)_2 + (CN)_2$
$Cu_2(CN)_2 + 6KCN \rightarrow 2K_3Cu (CN)_4$
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$2CuSO_4 + 10KCN \rightarrow 2K_3Cu(CN)_4 + 2K_2SO_4 + (CN)_2$