BCECE Medical BCECE Medical Solved Papers-2013

  • question_answer
    Calculate pH change when 0.01 mol\[C{{H}_{3}}KCOO\] Na solution is added to 1 L of\[0.01\,\,M\,C{{H}_{3}}COOH\] solution. \[Ka\,\,(C{{H}_{3}}COOH)=1.8\times {{10}^{-5}},\,pKa=4.74\]

    A)  3.37                

    B)  1.37

    C)  4.74                 

    D)  8.01

    Correct Answer: B

    Solution :

    \[pH\] of \[0.01\,M\,C{{H}_{3}}COOH\]                 \[pH=\frac{1}{2}\,[p{{K}_{a}}-\log \,C]\]                 \[=\frac{1}{2}\,(4.74-\log \,\,0.10)\]                 \[=\frac{1}{2}\,(4.74+2)=33.7\] When 0.01 mol \[C{{H}_{3}}COONa\] is added to it, it is now a buffer and \[[[C{{H}_{3}}COONa]=0.1]\,\,M\]. Now from                 \[pH=p{{K}_{a}}+\log \,\frac{[C{{H}_{3}}COO]}{[C{{H}_{3}}COOH]}\]                 \[=4.74+\log \frac{0.01}{0.01}=4.74\] \[\therefore \] Change in \[pH=4.74-3.37=1.37\]


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