WB JEE Medical WB JEE Medical Solved Paper-2012

  • question_answer
    20 mL 0.1 (N) acetic acid is mixed with 10 mL (N) solution of NaOH. The pH of the resulting solution is (\[p{{K}_{a}}\] of acetic acid is 4.74)

    A)  3.74   

    B)  4.74 

    C)  5.74  

    D)  6.74

    Correct Answer: B

    Solution :

     \[\underset{\begin{smallmatrix}  Initial\,20\,\times \,0.1\,=\text{2}\,\text{mmol} \\  \text{At}\,\text{time}\,\text{t}\,\text{(2-1)}\,\text{=}\,\text{mmol} \end{smallmatrix}}{\mathop{C{{H}_{3}}COOH}}\,+\,\,\,\,\underset{\begin{smallmatrix}  10\,\times \,0.1=1\,\text{mmol} \\  (1-1)\,=\,0\,\text{mmol} \end{smallmatrix}}{\mathop{NaOH}}\,\] \[\xrightarrow{{}}\underset{\text{1}\,\text{mmol}}{\mathop{C{{H}_{3}}COONa}}\,\,+{{H}_{2}}O\] From Hendersons equation, \[pH=p{{K}_{a}}+\log \frac{[C{{H}_{3}}COONa]}{[C{{H}_{3}}COOH]}\] \[=4.74+\log \frac{1}{1}\]   \[=4.74\]


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