BCECE Engineering BCECE Engineering Solved Paper-2013

  • question_answer
    Equilibrium constant for the reaction, \[N{{H}_{4}}OH+{{H}^{+}}NH_{4}^{+}+{{H}_{2}}O\]is  \[1.8\times {{10}^{9}}.\] Hence,    equilibrium   constant   for\[N{{H}_{3}}(aq)+{{H}_{2}}ONH_{4}^{+}+O{{H}^{-}}\]is

    A) \[1.8\times {{10}^{-5}}\]              

    B)        \[1.8\times {{10}^{5}}\]

    C)        \[1.8\times {{10}^{-9}}\]              

    D)        \[5.59\times {{10}^{-10}}\]

    Correct Answer: A

    Solution :

    \[N{{H}_{4}}OH+{{H}^{+}}NH_{4}^{+}+{{H}_{2}}O\] \[\therefore \]  \[K=\frac{[NH_{4}^{+}][{{H}_{2}}O]}{[N{{H}_{4}}OH][{{H}^{+}}]}=1.8\times {{10}^{9}}\] Again, \[N{{H}_{3}}+{{H}_{2}}O\xrightarrow{{}}N{{H}_{4}}OHNH_{4}^{+}+O{{H}^{-}}\] \[\therefore \] \[K=\frac{[NH_{4}^{+}][O{{H}^{-}}]}{[N{{H}_{4}}OH]}\] Now   \[\frac{K}{K}=\frac{[NH_{4}^{+}][O{{H}^{-}}]}{[N{{H}_{4}}OH]}\times \frac{[N{{H}_{4}}OH][{{H}^{+}}]}{[NH_{4}^{+}][{{H}_{2}}O]}\]                 \[=[O{{H}^{-}}][{{H}^{+}}]\]                        (\[\because \]\[{{\text{H}}_{\text{2}}}\text{O}\]is in excess) \[\text{=}\,{{\text{K}}_{w}}=1\times {{10}^{-14}}\]                 \[\therefore \]  \[K=K\,\times 1\times {{10}^{-14}}\]                                 \[=1.8\times {{10}^{9}}\times {{10}^{-14}}=1.8\times {{10}^{-5}}\]


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