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JEE Main & Advanced Chemistry Solutions / विलयन Sample Paper Topic Test - Solutions

  • question_answer
    The partial pressure of \[C{{O}_{2}}\] in air saturated with water vapours at \[25{}^\circ C\] and 1.00 atm is \[3.04\times {{10}^{-4}}\] atm. Henry's constant for \[C{{O}_{2}}\] in water is \[2.3\times {{10}^{-2}}\,\text{mol}\,{{\text{L}}^{-1}}\text{at}{{\text{m}}^{-1}}\] and for carbonic acid \[p{{K}_{a}}\] is 6.37. The pH of normal (\[C{{O}_{2}}\] mixed) rain water will be

    A) 7.42

    B) 6.37

    C) 6.99

    D) 5.76

    Correct Answer: D

    Solution :

    [d] Solubility \[=K\,{{p}_{C{{O}_{2}}}}\]
      \[=2.3\times {{10}^{-2}}\times 3.04\times {{10}^{-4}}\]
      \[=6.992\times {{10}^{-6}}\text{mol}\,{{\text{L}}^{-1}}\]
    \[{{H}_{2}}C{{O}_{3}}{{H}^{+}}+HCO_{3}^{-}\Rightarrow [{{H}^{+}}]=\sqrt{{{K}_{a}}.\,S}\]
    \[pH=\frac{1}{2}[p{{K}_{a}}-\log S]\]
                \[=\frac{1}{2}\left[ 6.37-\log 6.992\times {{10}^{-6}} \right]\]
                \[=\frac{1}{2}[6.37+5.16]\,\,\,\Rightarrow \,\,pH=5.76\]


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