JEE Main & Advanced Chemistry Electrochemistry / विद्युत् रसायन Question Bank Topic Test - Electrochemistry

  • question_answer
    For the cell \[Pt|{{H}_{2}}(g)|\] solution \[X||KCI\] (saturated) \[|H{{g}_{2}}C{{l}_{2}}|Hg|\,Pt\] the observed EMF at \[25{}^\circ C\] was \[600\text{ }mV.\] When solution X was replaced by a standard phosphate buffer with \[pH=7.00,\] the EMF was \[777\text{ }mV\]. Find the pH of solution X.

    A) 3

    B) 4           

    C) 5

    D) 6

    Correct Answer: B

    Solution :

    [b] \[{{H}_{2}}\xrightarrow{{}}2{{H}^{+}}+2{{e}^{-}}\]
    \[\frac{H{{g}_{2}}C{{l}_{2}}+2{{e}^{-}}\xrightarrow{{}}2Hg+2C{{l}^{-}}}{{{H}_{2}}+H{{g}_{2}}C{{l}_{2}}\xrightarrow{{}}2{{H}^{+}}+2C{{l}^{-}}+2Hg}\]
    \[{{E}_{initial}}=E{}^\circ +\frac{0.059}{2}\log \frac{1}{{{[{{H}^{+}}]}^{2}}\,{{[C{{l}^{-}}]}^{2}}}=0.6\]
    \[{{E}_{\text{final}}}=E{}^\circ +\frac{0.059}{2}\log \frac{1}{{{({{10}^{-7}})}^{2}}\,{{[C{{l}^{-}}]}^{2}}}=0.777\]
    subtracting we get
    \[0.177=0.059\log \frac{[{{H}^{+}}]}{{{10}^{-7}}}\]
    \[\Rightarrow \]   \[\frac{[{{H}^{+}}]}{{{10}^{-7}}}=1000\]
    \[\Rightarrow \]   \[[{{H}^{+}}]={{10}^{-4}}\]\[\Rightarrow \,\,\,\,pH=4.\]


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