RAJASTHAN PMT Rajasthan - PMT Solved Paper-1996

  • question_answer
    Given as: \[HF+{{H}_{2}}O\xrightarrow{ka}{{H}_{3}}{{O}^{+}}+{{F}^{-}}\] \[{{F}^{-}}+{{H}_{2}}O\xrightarrow{{{k}_{b}}}HF+O{{H}^{-}}\] Which relation is correct in the following?

    A)  \[{{K}_{b}}=K\omega \]

    B)                         \[{{K}_{b}}=1/K\omega \]

    C)                         \[{{K}_{a}}\times {{K}_{b}}={{K}_{\omega }}\]

    D)                         \[Ka/{{K}_{b}}=K\omega \]

    Correct Answer: C

    Solution :

    \[HF+{{H}_{2}}O\xrightarrow{{{K}_{a}}}{{H}_{3}}{{O}^{+}}+{{F}^{-}}\] \[{{K}_{a}}=\frac{[{{H}_{3}}{{O}^{+}}]\times [{{F}^{-}}]}{[HF]\times [{{H}_{2}}O]}\]        ??(1) \[{{F}^{-}}+{{H}_{2}}O\xrightarrow{kb}HF+O{{H}^{-}}\] \[{{K}_{b}}=\frac{[HF]\times [O{{H}^{-}}]}{[{{F}^{-}}][{{H}_{2}}O]}\] Multiply of equations (i) and (ii). \[{{K}_{a}}\times {{K}_{b}}=\frac{[{{H}_{3}}{{O}^{+}}][O{{H}^{-}}]}{{{[{{H}_{2}}O]}^{2}}}={{K}_{\omega }}\]                 \[{{K}_{a}}\times {{K}_{b}}={{K}_{\omega }}\]


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