Manipal Engineering Manipal Engineering Solved Paper-2009

  • question_answer
    \[{{10}^{-6}}M\,\,NaOH\]is diluted 100 times. The\[pH\]of the diluted base is

    A)  between 7 and 8

    B)  between 5 and 6

    C)  between 6 and 7

    D)  between 10 and 11

    Correct Answer: A

    Solution :

    \[[O{{H}^{-}}]\]in the diluted base\[=\frac{{{10}^{-6}}}{{{10}^{2}}}={{10}^{-8}}\] Total\[[O{{H}^{-}}]={{10}^{-8}}+[O{{H}^{-}}]\]of water                 \[=({{10}^{-8}}+{{10}^{-7}})M\]                 \[={{10}^{-8}}[1+10]M\]                 \[=11\times {{10}^{-8}}M\]     \[pOH=-\log 11\times {{10}^{-8}}\]                 \[=-\log 11+8\log 10\]                 \[=6.9586\]                 \[pH=14-6.9586\]                        \[=7.0414\]


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