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Manipal Medical Manipal Medical Solved Paper-2013

  • question_answer
    In qualitative analysis, when\[{{H}_{2}}S\]is passed through an aqueous solution of salt acidified with dil.\[HCl,\]a black precipitate is obtained. On boiling the precipitate with dil\[HN{{O}_{3}},\]it forms a solution of blue colour. Addition of excess of aqueous solution of ammonia to this solution gives

    A)  deep blue precipitate of\[Cu{{(OH)}_{2}}\]

    B)  deep blue solution of \[{{[Cu{{(N{{H}_{3}})}_{4}}]}^{2+}}\]

    C)  deep blue solution of \[Cu{{(N{{O}_{3}})}_{2}}\]

    D)  deep blue solution of \[Cu{{(OH)}_{2}}.Cu{{(N{{O}_{3}})}_{2}}\]

    Correct Answer: B

    Solution :

     \[\underset{Salt}{\mathop{CuS{{O}_{4}}}}\,+{{H}_{2}}S\xrightarrow[{}]{{}}\underset{black\,ppt}{\mathop{CuS}}\,+{{H}_{2}}S{{O}_{4}};\] \[CuS+2HN{{O}_{3}}\xrightarrow[{}]{{}}\underset{blue\,solution}{\mathop{Cu{{(N{{O}_{3}})}_{2}}}}\,+{{H}_{2}}S;\] \[Cu{{(N{{O}_{3}})}_{2}}+4N{{H}_{3}}\xrightarrow[{}]{{}}\underset{deep\,blue\,solution}{\mathop{{{[Cu{{(N{{H}_{3}})}_{4}}]}^{2+}}}}\,+2NO_{3}^{-}\]


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