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RAJASTHAN PMT Rajasthan - PMT Solved Paper-2000

  • question_answer
    The hydrogen ion concentration in a solution of weak acid of dissociation constant \[{{K}_{a}}\]  and concentration C is nearly equal to:

    A)  \[{{K}_{a}}.C\] 

    B)                                         \[C/{{K}_{a}}\]

    C)         \[\sqrt{{{K}_{a}}.C}\]                    

    D)         \[\sqrt{{{K}_{a}}/C}\]

    Correct Answer: D

    Solution :

    \[HA{{H}^{+}}+{{A}^{-}}\] \[{{K}_{a}}=\frac{{{C}^{2}}{{x}^{2}}}{C(a-x)}\] \[\frac{{{C}^{2}}{{x}^{2}}}{C}\](For weak acid\[1-x=1\]) \[C.\,{{K}_{a}}={{C}^{2}}{{x}^{2}}=Cx=\sqrt{{{K}_{a}}.C}\] \[\therefore \]  \[[{{H}^{+}}]=Cx=\sqrt{{{K}_{a}}.C}\]


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