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Uttarakhand PMT Uttarakhand PMT Solved Paper-2007

  • question_answer
    0.01 M solution of\[{{H}_{2}}A\]has pH equal to 4, if \[{{K}_{{{a}_{1}}}}\]for the acid is\[4.45\times {{10}^{-7}},\]the concentration of\[H{{A}^{-}}\]ion in solution would be

    A)  0.01 N         

    B)  \[4.45\times {{10}^{-5}}\]

    C)  \[8.0\times {{10}^{-5}}\]      

    D)  unpredictable

    Correct Answer: B

    Solution :

     \[{{H}_{2}}A{{H}^{+}}+H{{A}^{-}}\] as          \[pH=4[{{H}^{+}}]={{10}^{-4}}M\] \[{{K}_{{{a}_{1}}}}=\frac{[{{H}^{+}}][H{{A}^{-}}]}{[{{H}_{2}}A]}\] Or \[\frac{{{10}^{-4}}\times [H{{A}^{-}}]}{{{10}^{-2}}}=4.45\times {{10}^{-7}}\] Or \[[H{{A}^{-}}]=4.45\times {{10}^{-5}}\]


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