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MGIMS WARDHA MGIMS WARDHA Solved Paper-2007

  • question_answer
    A buffer solution contains 500 mL of 0.2 M \[C{{H}_{3}}COONa\]and 500 mL of\[0.1\text{ }M\text{ }C{{H}_{3}}COOH\]. 1L of water is added to this buffer, pH before and after dilution will be (\[p{{k}_{a}}\] of\[C{{H}_{3}}COOH=4.74\])

    A)  5.04, 3.74           

    B)  5.04, 5.04

    C)  5.04, 4.89           

    D)  9.56, 9.56

    Correct Answer: B

    Solution :

                     \[C{{H}_{3}}COONaC{{H}_{3}}CO{{O}^{-}}+N{{a}^{+}}\] pH of buffer \[=p{{K}_{a}}+\log \frac{[C{{H}_{3}}CO{{O}^{-}}]}{[C{{H}_{3}}COOH]}\]                 \[=4.74+\log \frac{500\times 0.2}{500\times 0.1}\]                 \[=4.74+\log \frac{500\times 0.2}{500\times 0.1}\]                 \[=5.04\]              pH of a buffer does not change with dilution.


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