KVPY Sample Paper KVPY Stream-SX Model Paper-4

  • question_answer
    A metal complex having composition \[Cr{{(N{{H}_{3}})}_{4}}C{{l}_{2}}Br\] has been isolated in two forms A and B. A reacts with\[AgN{{O}_{3}}\]producing a white precipitate which was soluble in dilute ammonia solution. B reacts with \[AgN{{O}_{3}}\] producing a pale yellow precipitate soluble in concentrated ammonia solution. The formulae of A and B are respectively

    A) \[[Cr\,{{(N{{H}_{3}})}_{4}}Br]\,C{{l}_{2}};[Cr\,(N{{H}_{3}})C{{l}_{2}}]\,Br\]

    B) \[[Cr\,{{(N{{H}_{3}})}_{4}}BrCl]\,Cl;[Cr\,(N{{H}_{3}})C{{l}_{2}}Br]\,N{{H}_{3}}\]

    C) \[[Cr\,{{(N{{H}_{3}})}_{4}}C{{l}_{2}}]Br;[Cr\,(N{{H}_{3}})\,BrCl]\,Cl\]

    D) \[[Cr\,{{(N{{H}_{3}})}_{4}}BrCl]\,Cl;[Cr\,{{(N{{H}_{3}})}_{4}}C{{l}_{2}}]\,Br\]

    Correct Answer: D

    Solution :

    [d]
    Since, the compound A gives white precipitate with \[AgN{{O}_{3}},\] which is soluble in dilute ammonia solution, it contains at least one \[Cl\] atom outside the coordination sphere. Thus, its formula [a] is \[[Cr\,{{(N{{H}_{3}})}_{4}}BrCl]\,Cl.\]
    \[[Cr\,{{(N{{H}_{3}})}_{4}}BrCl]\,Cl\xrightarrow{{}}{{[Cr\,{{(N{{H}_{3}})}_{4}}BrCl]}^{+}}C{{l}^{-}}\]
    \[AgN{{O}_{3}}+C{{l}^{-}}\xrightarrow{{}}\underset{\text{White}\,\text{ppt}.}{\mathop{AgCl}}\,+NO_{3}^{-}\]
    Further, the compound B on reaction with\[AgN{{O}_{3}}\]produces a pale yellow precipitate soluble in cone. \[N{{H}_{3}}\]solution.
    Thus, \['B'\]is \[[Cr\,{{(N{{H}_{3}})}_{4}}C{{l}_{2}}]Br\]\[[Cr\,{{(N{{H}_{3}})}_{4}}C{{l}_{2}}]Br\xrightarrow{{}}{{[Cr{{(N{{H}_{3}})}_{4}}C{{l}_{2}}]}^{+}}+B{{r}^{-}}\]
    \[AgN{{O}_{3}}+B{{r}^{-}}\xrightarrow{{}}\underset{\text{Pale}\,\text{yellolw}\,\text{ppt}\text{.}}{\mathop{AgBr}}\,+NO_{3}^{-}\]


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