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AMU Medical AMU Solved Paper-2005

  • question_answer
    How much sodium acetate should be added to M solution of \[C{{H}_{3}}COOH\] to give a solution of pH 5.5. (\[p{{K}_{a}}\] of \[C{{H}_{3}}COOH=4.5\]) ?

    A)  0.1 M                                   

    B)  0.2 M

    C)  1.0 M                                   

    D)  10.0 M

    Correct Answer: C

    Solution :

                     Key Idea \[pH=p{{K}_{a}}+\log \,\frac{[salt]}{[acid]}\] Here,     pH = 5.5,              \[p{{K}_{a}}=4.5\] Concentration of \[C{{H}_{3}}COOH=0.1\,\,M\]                 \[pH=p{{K}_{a}}+\log \,\frac{[C{{H}_{3}}COONa]}{[C{{H}_{3}}COOH]}\]                 \[5.5=4.5+\log \frac{[C{{H}_{3}}COONa]}{0.1}\]                 \[1.0=\log \frac{[C{{H}_{3}}COONa]}{0.1}\]                 \[10=\frac{[C{{H}_{3}}COONa]}{0.1}\] \[[C{{H}_{3}}COONa]=10\times 0.1=1.0\,M\]


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