J & K CET Medical J & K - CET Medical Solved Paper-2015

  • question_answer
    HA is a weak acid. At\[25{}^\circ C,\]the molar conductivity of 0.02 M HA is\[150\,{{\Omega }^{-1}}c{{m}^{2}}mo{{l}^{-1}}.\]If its\[\Lambda _{m}^{o}\]is\[300\,{{\Omega }^{-1}}c{{m}^{2}}mo{{l}^{-1}},\]then equilibrium constant of HA dissociation is

    A)  0.001  

    B)  0.005  

    C)  0.01   

    D)  0.02

    Correct Answer: C

    Solution :

     Given, molar conductivity \[({{\Lambda }_{m}})=300\,{{\Omega }^{-1}}c{{m}^{2}}mo{{l}^{-1}}\] Limiting molar conductivity \[(\Lambda _{m}^{o})=150\,{{\Omega }^{-1}}c{{m}^{2}}mo{{l}^{-1}}\] Concentration  = 0.02 M \[\therefore \]Degree of dissociation\[(\alpha )=\frac{{{\Lambda }_{m}}}{\Lambda _{m}^{o}}\] \[\alpha =\frac{150}{300}=0.5\] Now, by using following reaction, we can determine the value of its dissociation constant \[{{K}_{a}}=\frac{C{{\alpha }^{2}}}{(1-\alpha )}\] \[{{K}_{a}}=\frac{0.02\times {{(0.5)}^{2}}}{(1-0.5)}\] \[=\frac{0.02\times 0.5\times 0.5}{0.5}=0.01\]


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