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RAJASTHAN ­ PET Rajasthan PET Solved Paper-2011

  • question_answer
    A buffer solution with pH 9 is to be prepared by mixing\[N{{H}_{4}}Cl\]and\[N{{H}_{4}}OH\]. Calculate the number of moles of\[N{{H}_{4}}Cl\]that should be added to 1 L of\[1.0\text{ }M\text{ }N{{H}_{4}}OH\].

    A)  3.4              

    B)  2.6

    C)  1.5              

    D)  1.99

    Correct Answer: D

    Solution :

     \[pOH=-\log {{K}_{b}}+\log \left[ \frac{salt}{base} \right]\] \[[14-pH]=-\log [1.8\times {{10}^{-5}}]+\left[ \frac{salt}{1.0} \right]\] \[5=4.7+\log \left[ \frac{salt}{1.0} \right]\] \[\log \left[ \frac{salt}{1.0} \right]=5-4.7=0.3\] \[[salt]=antilog\text{ }0.3\] \[[salt]=1.995\]


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