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NEET AIPMT SOLVED PAPER SCREENING 2011

  • question_answer
    A buffer solution is prepared in which the concentration of \[N{{H}_{3}}\] is 0.30 M and the concentration of \[\text{NH}_{\text{4}}^{\text{+}}\] is 0.20 M. If the equilibrium constant, \[{{K}_{b}}\] for \[N{{H}_{3}}\] equals \[1.8\times {{10}^{-5}},\] what is the pH of this solution? (log 2.7 =0.43)

    A)  9.43                      

    B)         11.72   

    C)         8.73                      

    D)         9.08

    Correct Answer: A

    Solution :

    \[pOH=p{{K}_{b}}+\log \frac{[Salt]}{[Base]}\] \[=-\log {{K}_{b}}+\log \frac{[Salt]}{[Base]}\] \[=-\log 1.8\times {{10}^{-5}}+\log \frac{0.20}{0.30}\] \[=5-0.25+(-0.176)\] \[=4.75-0.176=4.57\] \[\therefore \]\[pH=14-4.57=9.43\]


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