A) CuCN
B) \[{{[Cu{{(CN)}_{4}}]}^{3-}}\]
C) \[{{[Cu{{(CN)}_{4}}]}^{2-}}\]
D) \[Cu\,{{(CN)}_{2}}\]
Correct Answer: B
Solution :
Copper sulphate on reaction with KCN to give cupric cyanide precipitates firstly which reduce into \[C{{u}_{2}}C{{N}_{2}}\] and dissolve in excess of KCN to give soluble \[{{K}_{3}}[Cu{{(CN)}_{4}}]\] complex salt \[[CuS{{O}_{4}}+2KCN\to \underset{\begin{smallmatrix} Cupric \\ cyanide \end{smallmatrix}}{\mathop{Cu{{(CN)}_{2}}}}\,+{{K}_{2}}S{{O}_{4}}]\times 2\] \[2Cu{{(CN)}_{2}}\to C{{u}_{2}}{{(CN)}_{2}}\to \underset{Cyanogen}{\mathop{NC-CN}}\,\] \[C{{u}_{2}}{{(CN)}_{2}}+6KCN\to \underset{so\operatorname{lub}le\,complex\,salt}{\mathop{2{{K}_{3}}[Cu{{(CN)}_{4}}]}}\,\] _______________________________________ \[2CuS{{O}_{4}}+10KCN\to 2{{K}_{3}}[Cu{{(CN)}_{4}}+2{{K}_{2}}S{{O}_{4}}+{{(CN)}_{2}}]\]
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