JEE Main & Advanced JEE Main Paper Phase-I (Held on 09-1-2020 Evening)

  • question_answer
    The solubility product of \[Cr{{(OH)}_{3}}\] at \[298\text{ }K\]is\[6.0\times {{10}^{31}}\]. The concentration of hydroxide ions in a saturated solution of \[Cr{{(OH)}_{3}}\] will be [JEE MAIN Held on 09-01-2020 Evening]

    A) \[{{(2.22\times {{10}^{-31}})}^{1/4}}\]

    B) \[{{(18\times {{10}^{-31}})}^{1/2}}\]

    C) \[{{(18\times {{10}^{-31}})}^{1/4}}\]

    D) \[{{(4.86\times {{10}^{-29}})}^{1/4}}\]

    Correct Answer: C

    Solution :

    \[Cr{{(OH)}_{3}}\underset{S}{\mathop{C{{r}^{3+}}}}\,+{{\underset{3S}{\mathop{3O{{H}^{-}}}}\,}_{\text{ }\!\![\!\!\text{ S}\,\,\text{is}\,\,\text{solubility }\!\!]\!\!\text{ }}}\] \[\therefore \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,27{{S}^{4}}=6\times {{10}^{-31}}\]             \[S={{\left( \frac{6}{27}\times {{10}^{-31}} \right)}^{1/4}}\] \[\because \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,[O{{H}^{-}}]=3S\]             \[=3{{\left( \frac{6}{27}\times {{10}^{-31}} \right)}^{1/4}}\]             \[={{(18\times {{10}^{-31}})}^{1/4}}\]


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