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JEE Main & Advanced Sample Paper JEE Main Sample Paper-16

  • question_answer
    An aqueous solution contain\[5M\,Ca{{(OH)}_{2}}\And .1M\,N{{H}_{4}}OH\,{{K}_{b}}({{10}^{-5}})\]. Then \[(N{{H}_{4}}^{+})\]will be equal to-

    A) \[{{10}^{-4}}M\]                              

    B) \[{{10}^{-6}}M\]

    C) \[2\times {{10}^{-6}}M\]                             

    D) \[2\times {{10}^{-5}}M\]

    Correct Answer: B

    Solution :

    \[\underset{0}{\mathop{Ca{{(OH)}_{2}}}}\,\] \[\xrightarrow[{}]{{}}\]\[\underset{0.5}{\mathop{C{{a}^{2+}}}}\,\]+ \[\underset{1+x}{\mathop{2O{{H}^{-}}}}\,\]
    \[\underset{0.1-x}{\mathop{N{{H}_{4}}OH}}\,\] \[\xrightarrow[{}]{{}}\]\[\underset{x}{\mathop{N{{H}_{4}}^{+}}}\,\]+ \[\underset{1+x}{\mathop{O{{H}^{-}}}}\,\]
    \[{{K}_{b}}={{10}^{-5}}\] \[\therefore \]\[{{10}^{-5}}=\frac{x.\left( 1+x \right)}{\left( 0.1-x \right)}\]As x is very small \[\therefore \]\[{{10}^{-5}}=\frac{x}{0.1}\]\[\Rightarrow \]\[x={{10}^{-6}}M\]


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