JEE Main & Advanced Sample Paper JEE Main - Mock Test - 10

  • question_answer
    If the concentration of \[O{{H}^{-}}\] ions in the reaction  \[Fe{{(OH)}_{3}}(s)\rightleftharpoons F{{e}^{3+}}(aq)+3O{{H}^{-}}(aq)\] is decreased by \[\frac{1}{4}\] times, then equilibrium concentration of \[F{{e}^{3+}}\] will increase by:

    A) 8 times             

    B) 16 times

    C) 64 times                       

    D) 4 times

    Correct Answer: B

    Solution :

    For this reaction \[{{K}_{eq.}}\] is given by \[K=\frac{\left[ F{{e}^{3+}} \right]{{\left[ O{{H}^{-}} \right]}^{3}}}{\left[ Fe{{\left( OH \right)}_{3}} \right]}\]
    \[=\left[ F{{e}^{3+}} \right]\,{{\left[ O{{H}^{-}} \right]}^{3}}\]       \[\left[ \because \,\,\left[ soild \right]=1 \right]\]
    If \[\left[ O{{H}^{-}} \right]\] is decreased by \[\frac{1}{4}\] times then for reaction equilibrium constant to remain constant, we have to increase the concentration of \[\left[ F{{e}^{3+}} \right]\] by a factor of \[{{4}^{3}}\] i.e., \[4\times 4\times 4=64.\]


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