BHU PMT BHU PMT Solved Paper-2003

  • question_answer
    \[NaOH(aq),~~HCl(aq),\]and \[NaCl(aq)\] concentration of each is\[{{10}^{-3}}M\]. Their pH will be respectively:

    A)  10, 6, 2                                

    B)  11, 3, 7

    C)  10, 3, 7                                

    D)  10, 4, 7

    Correct Answer: B

    Solution :

                     Key Idea: Use \[pH=-\log [{{H}^{+}}]\] and\[pH-\text{ }pOH=14\]to solve problem. pH of \[{{10}^{-3}}M\,NaOH\] \[\underset{{{10}^{-3}}M}{\mathop{NaOH}}\,\xrightarrow[{}]{{}}N{{a}^{+}}+\underset{{{10}^{-3}}M}{\mathop{O{{H}^{-}}}}\,\] \[pOH=-\log {{10}^{-3}}\]                 \[=3\] \[pH+pOH=14\] \[pH=14-3=11\] \[\mathbf{PH}\]of\[\mathbf{1}{{\mathbf{0}}^{\mathbf{-3}}}\mathbf{HCl}\]                 \[\underset{{{10}^{-3}}M}{\mathop{HCl}}\,\xrightarrow[{}]{{}}\underset{{{10}^{-3}}M}{\mathop{{{H}^{+}}}}\,+C{{l}^{-}}\] \[pH=-\log [{{H}^{+}}]\] \[=-\log [{{10}^{-3}}]\] \[=3\] pH of\[{{10}^{-3}}NaCl\]is 7 (neutral) \[\because \]It is salt of strong acid and strong base.


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