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CMC Medical CMC-Medical VELLORE Solved Paper-2009

  • question_answer
    Which compound is insoluble in dilute \[HN{{O}_{3}}\] and dissolved in aqua regia?

    A)  \[HgS\]                               

    B)  \[CuS\]

    C)  \[B{{i}_{2}}{{S}_{3}}\]                   

    D)  \[PbS\]

    Correct Answer: A

    Solution :

                    Except \[HgS,\]all other sulphides of second (IIA) group of qualitative analysis are soluble in dilute \[HN{{O}_{3}}\] but \[HgS\] is soluble only in aqua regia (a mixture of 3 part\[HCl\]and 1 part\[HN{{O}_{3}}\]). \[3HgS+\underbrace{2HN{{O}_{3}}+6HCl}_{aqua\,\,regia}\xrightarrow{{}}3HgC{{l}_{2}}+3S\]  \[+2NO+4{{H}_{2}}O\]


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