VMMC VMMC Medical Solved Paper-2011

  • question_answer
    The values of observed and calculated molecular masses of \[\text{Ca(N}{{\text{O}}_{\text{3}}}{{\text{)}}_{\text{2}}}\]are 164 and 65.4 respectively. Its degree of dissociation will be

    A) 25%                       

    B)        50%                       

    C)  75%                      

    D)         80%

    Correct Answer: C

    Solution :

    \[\begin{align}   & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,Ca{{(N{{O}_{3}})}_{2}}\rightleftharpoons C{{a}^{2+}}+2NO_{3}^{-} \\  & \text{Initially}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{1}\,\text{mol}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{0}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{0} \\  & \text{At }\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(1-x)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,2x \\  & \text{equilibrium} \\ \end{align}\] Total number of particles (moles) at equilibrium    \[\,\,\,=(1-x)\,+x+2x\,\,\,\] \[=(1+2x)\] \[\text{Now,}\frac{\text{calculated}\,\text{molecular}\,\text{mass}}{\text{normal}\,\text{molecular}\,\text{mass}}\] \[\text{=}\frac{\text{number}\,\text{of}\,\text{particles}\,\text{after}\,\text{dissociation}}{\text{number}\,\text{of}\,\text{particles}\,\text{before}\,\text{dissociation}}\]                \[\frac{164}{65.4}=\frac{1+2x}{1}\]                 or            \[\frac{164-65.4}{65.4}=2x\] or            \[x=\frac{98.6}{65.4\times 2}=0.7538\] or degree of dissociation of \[\text{Ca(N}{{\text{O}}_{\text{3}}}{{\text{)}}_{\text{2}}}\] \[=0.7538\times 100=75.38%\]


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