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JEE Main & Advanced Sample Paper JEE Main - Mock Test - 14

  • question_answer
    Arrange the following in order of decreasing molar conductivity in aqueous solution:
    I. \[Li[Co{{(N{{H}_{3}})}_{2}}{{(N{{O}_{2}})}_{4}}]\]    
    II. \[Na[Co{{(N{{H}_{3}})}_{2}}{{(N{{O}_{2}})}_{4}}]\]  
    III. \[K[Co{{(N{{H}_{3}})}_{2}}{{(N{{O}_{2}})}_{4}}]\]   
    IV. \[Cs[Co{{(N{{H}_{3}})}_{2}}{{(N{{O}_{2}})}_{4}}]\]

    A) \[I>II>III>IV\]           

    B) \[II>IIl>IV>I\]   

    C)     \[IV>III>II>I\]  

    D)               \[III>II>I>IV\]

    Correct Answer: C

    Solution :

    [c] The above mentioned complexes ionises as follows:
    (I)  \[Li[Co{{(N{{H}_{3}})}_{2}}{{(N{{O}_{2}})}_{4}}]\xrightarrow{{}}\]\[L{{i}^{\oplus }}_{(aq)}+{{[Co{{(N{{H}_{3}})}_{2}}{{(N{{O}_{2}})}_{4}}]}^{\bigcirc -}}_{(aq)}\]
    (II) \[Na[Co{{(N{{H}_{3}})}_{2}}{{(N{{O}_{2}})}_{4}}]\xrightarrow{{}}\]\[N{{a}^{\oplus }}_{(aq)}+{{[Co{{(N{{H}_{3}})}_{2}}{{(N{{O}_{2}})}_{4}}]}^{\bigcirc -}}_{(aq)}\]
    (III) \[K[Co{{(N{{H}_{3}})}_{2}}{{(N{{O}_{2}})}_{4}}]\xrightarrow{{}}\]\[{{K}^{\oplus }}_{(aq)}+{{[Co{{(N{{H}_{3}})}_{2}}{{(N{{O}_{2}})}_{4}}]}^{\bigcirc -}}_{(aq)}\]
    (IV) \[Cs[Co{{(N{{H}_{3}})}_{2}}{{(N{{O}_{2}})}_{4}}]\xrightarrow{{}}\]\[C{{s}^{\oplus }}_{(aq)}+{{[Co{{(N{{H}_{3}})}_{2}}{{(N{{O}_{2}})}_{4}}]}^{\bigcirc -}}_{(aq)}\]
    In all the cases, the number of ionic species produced are same (two in each case), the number of charges produced are same (\[+1\] or\[-1\]). Molar conductivity depends directly on the mobility or movement of species produced on ionisation. Mobility of ions \[\propto \] charge density. Since the charge density (ionic charge/ionic radius) decreases and hence the mobilities of ions should be in the order as: \[L{{i}^{\oplus }}>N{{a}^{\oplus }}>{{K}^{\oplus }}>C{{s}^{\oplus }}\] But in aqueous solution, the above order of mobilities is reversed, because hydration \[\propto \] charge density \[\propto \]mobilities. So \[L{{i}^{\oplus }}\] ion is extensively hydrated than \[C{{s}^{\oplus }}\]ion and hence the mobilities and conductance of the above compounds is in the order\[IV>III>II>I\].


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