KVPY Sample Paper KVPY Stream-SX Model Paper-15

  • question_answer
    On treatment of 100 mL of 0.1 M solution of \[CoC{{l}_{3}}.6{{H}_{2}}O\] with excess of \[AgN{{O}_{3}};1.2\times {{10}^{22}}\] ions are precipitated. The complex is

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

    B) \[[Co\,{{({{H}_{2}}O)}_{3}}C{{l}_{3}}]\cdot 3{{H}_{2}}O\]

    C) \[[Co\,{{({{H}_{2}}O)}_{6}}]C{{l}_{3}}\]

    D) \[[Co\,{{({{H}_{2}}O)}_{5}}Cl]\,C{{l}_{2}}\cdot {{H}_{2}}O\]

    Correct Answer: D

    Solution :

    Molarity (M) \[\text{=}\frac{\text{Number}\,\text{of}\,\text{moles}\,\text{of}\,\text{solute}}{\text{Volume}\,\text{of}\,\text{slution}\,\text{(in}\,\text{L)}}\]
    \[\therefore \]Number of moles of complex
    \[=\frac{\text{Molarity}\times \text{volume}\,(\text{in}\,\text{mL})}{1000}\]\[=\frac{0.1\times 100}{1000}=0.01\,mol\]
    Number of moles of ions precipitate \[=\frac{1.2\times {{10}^{22}}}{6.02\times {{10}^{23}}}\]\[=0.02\,mol\]
    Number of \[C{{l}^{-}}\]present in ionization sphere
    \[\text{=}\frac{\text{Number}\,\text{of}\,\text{moles}\,\text{of}\,\text{ions}\,\text{precipitated}}{\text{Number}\,\text{of}\,\text{moles}\,\text{of}\,\text{complex}}\]\[=\frac{0.02}{0.01}=2\]
    \[\therefore \]\[2\,C{{l}^{-}}\]are present outside the square brackets, i.e. in iomsation sphere. Thus, the formula of complex is
    \[[Co{{({{H}_{2}}O)}_{5}}Cl]C{{l}_{2}}\cdot {{H}_{2}}O\]


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