AIIMS AIIMS Solved Paper-2014

  • question_answer
    A solution containing 0.319 g of\[\text{CrC}{{\text{l}}_{3}}\text{.6}{{\text{H}}_{2}}O\]was passed through a cation exchange resin and acid coming out of the cation exchange resin required 28.5 mL of 0.125 M\[NaOH\]. Determine correct formula of the complex [mol. wt. of the complex =266.5]

    A) \[[Cr({{H}_{2}}{{O}_{6}})]C{{l}_{3}}\] 

    B) \[[Cr({{H}_{2}}{{O}_{5}})Cl]{{H}_{2}}O.C{{l}_{2}}\]

    C) \[[Cr{{({{H}_{2}}O)}_{4}}C{{l}_{2}}]Cl.2{{H}_{2}}O\]

    D) \[[Cr{{({{H}_{2}}O)}_{3}}C{{l}_{3}}]3{{H}_{2}}O\]

    Correct Answer: A

    Solution :

    When the solution of the complex is passed through cation exchanger, \[nC{{l}^{-}}\] ions will combine with H4' (of cation exchanger) to form HCI \[nC{{l}^{-}}+n{{H}^{+}}\to nHCl\] \[\because \]1 mol of the complex will form n moles of \[HCl\]. \[\therefore \]1 mole of complex n mol \[HCl\] = n moles of\[\text{NaOH}\] Mole of the complex \[=\frac{0.319}{266.5}\]                                 \[=0.0012\]mol mole of \[\text{NaOH}\]used \[=\frac{28.5\times 0.125}{1000}\] \[=\text{ }0.00\text{36 mol}\] 0.0012 mol of complex = 0.0036 mol \[\text{NaOH}\] \[=0.00\text{36 mol HC}l\] mol complex \[=\frac{0.0036}{0.0012}=\] 3 mol HCI Thus, all the \[C{{l}^{-}}\]ions are outside of the coordination sphere. Hence, complex is \[[Cr{{({{H}_{2}}O)}_{6}}C{{l}_{3}}]\].                


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