NEET AIPMT SOLVED PAPER 2002

  • question_answer
                    \[CuS{{O}_{4}}\] when reacts with KCN forms CuCN. Which is insoluble in water. It is soluble in excess of KCN, due to formation of the following complex:                                                                                                        

    A)                 \[{{K}_{2}}[Cu{{(CN)}_{4}}]\]

    B)                 \[[{{K}_{3}}{{(CuCN)}_{4}}]\]

    C)                 \[CuC{{N}_{2}}\]

    D)                 \[Cu[K\,Cu{{(CN)}_{4}}]\]

    Correct Answer: B

    Solution :

                    \[CuS{{O}_{4}}\] reacts with KCN gives a white precipitate of cuprous cyanide and cyanogen gas. The cuprous cyanide dissolves in excess of KCN forming \[K\,[Ag{{(CN)}_{4}}]\].                 \[CuS{{O}_{4}}+2KCN\xrightarrow{{}}{{K}_{2}}S{{O}_{4}}+Cu{{(CN)}_{2}}\] \[2Cu{{(CN)}_{2}}\xrightarrow{{}}\underset{\text{insoluble}}{\mathop{2CuCN}}\,+\underset{\text{cyanogen}}{\mathop{CN-CN}}\,\]                 \[CuCN+3KCN\xrightarrow{{}}\underset{\text{soluble}}{\mathop{{{K}_{3}}[Cu{{(CN)}_{4}}]}}\,\]


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