AMU Medical AMU Solved Paper-2010

  • question_answer
    The pH of a solution prepared by mixing 2.0 mL of HCl solution of pH 3.0 and 3.0 mL of NaOH of pH 10.0 is

    A)  2.5                                        

    B)  3.5

    C)  5.5                                        

    D)  6.5

    Correct Answer: B

    Solution :

                     \[\because \] pH of HCl solution =3.0 \[\therefore \,[{{H}^{+}}]\] in HCl solution \[=1\times {{10}^{-3}}\] \[\therefore \] pH of NaOH solution =10.0 \[\therefore \,\,[{{H}^{+}}]\] in NaOH solution \[=1\times {{10}^{-10}}\] \[[O{{H}^{-}}]\] in NaOH solution \[=\frac{1\times {{10}^{-14}}}{1\times {{10}^{-10}}}\] Mill equivalents of \[HCl={{N}_{1}}{{V}_{1}}=2.0\times 1\times {{10}^{-3}}\]                                                 \[=2.0\times {{10}^{-3}}\] Mill equivalents of NaOH \[=3.0\times 1\times {{10}^{-4}}\]                                                 \[=3.0\times {{10}^{-4}}\] Since, mill equivalents of HCl are in excess, the mill equivalents of \[[{{H}^{+}}]\] in mixture                 \[=(2.0\times {{10}^{-3}})-(3.0\times {{10}^{-4}})\]                 \[=1.7\times {{10}^{-3}}\] Concentration of \[[{{H}^{+}}]\] in mixture                 \[=\frac{1.7\times {{10}^{-3}}}{3+2}=3.4\times {{10}^{-4}}\] pH of mixture \[=-\log [{{H}^{+}}]\]                 \[=-\log \,(3.4\times {{10}^{-4}})\]                 = 3.5


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