NEET Sample Paper NEET Sample Test Paper-87

  • question_answer
    When concentrated HCl is added to an aqueous solution of \[CoC{{l}_{2}},\] its colour changes from reddish pink to deep blue. Which complex ion gives blue colour in this reaction?

    A) \[{{[CoC{{l}_{4}}]}^{2-}}\]

    B)        \[{{[CoC{{l}_{6}}]}^{3-}}\]

    C) \[{{[CoC{{l}_{6}}]}^{4-}}\]    

    D)        \[{{[Co{{({{H}_{2}}O)}_{6}}]}^{2+}}\]

    Correct Answer: A

    Solution :

    [a] Aqueous solution of \[CoC{{l}_{2}}\] contains \[{{[Co{{({{H}_{2}}O)}_{6}}]}^{2+}}\] which is pinkish in colour so option [d] is incorrect. Reduction potential of \[C{{o}^{3+}}\xrightarrow{{}}C{{o}^{2+}}\] is high so option [b] is incorrect. \[C{{o}^{2+}}\] does not oxidises easily to \[C{{o}^{3+}}.\] It is general case that symmetrical substituted octahedral complexes are less deeper in colour than tetrahedral complexes. So \[{{[CoC{{l}_{4}}]}^{2-}}\] is deep blue in colour.    


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