JEE Main & Advanced Sample Paper JEE Main - Mock Test - 22

  • question_answer
    Two buffer solutions A and B each made with benzoic acid a d sodium benzoate differ in their pH by two units.  A has salt: acid\[=a:b\].  B has salt: acid \[b:a.\]. If \[a>b,\]then the value of \[a:b\] is

    A) \[3:17\]               

    B)        \[10:0\]          

    C) \[3:0\]               

    D)        \[6:0\]

    Correct Answer: B

    Solution :

        [b] Buffer A \[p{{H}_{A}}=p{{K}_{a}}+\log \left( \frac{a}{b} \right)\]                  ?..(i) Buffer B \[p{{H}_{B}}=p{{K}_{a}}+\log \left( \frac{b}{a} \right)\]              ??(ii) Since \[a>b\] \[\therefore \,\,\,\,p{{H}_{A}}-p{{H}_{B}}=\log \frac{a}{b}-\log \frac{b}{a}\] \[2=\log \frac{a}{b}+\log \frac{a}{b}\] \[\Rightarrow \,\,\,\,\,2=2\log \frac{a}{b}\] \[\therefore \,\,\,\,\,\log \frac{a}{b}=1\] \[\frac{a}{b}=\]Antilog \[(1)=10\] \[\therefore \,\,\,\,\,\frac{a}{b}=10\]


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