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JEE Main & Advanced Sample Paper JEE Main - Mock Test - 31

  • question_answer
    A buffer solution is prepared by mixing 0.1 M ammonia and M ammonium chloride. At 298 K, the \[{{\operatorname{pK}}_{b}}\,of\,\,N{{H}_{4}}OH\] is 5.0. The pH of the buffer is

    A) 10.0     

    B)        9.0

    C) 6.0                   

    D)        8.0

    Correct Answer: A

    Solution :

    The pOH of a buffer consisting of \[N{{H}_{3}}\] (i.e. \[N{{H}_{4}}OH\]) and salt \[N{{H}_{4}}Cl\] (salt) is given by the equation \[pOH=p{{K}_{b}}+\log \frac{\left[ ammonia \right]}{\left[ salt \right]}=5.0+\log \,\frac{\left[ 0.1 \right]}{\left[ 1.0 \right]}\] \[=5.0 -log 10 =5-1=4.0\] \[\therefore  \,\,pH= 14-pOH= 14-4.0= 10\]


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