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CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2003

  • question_answer
    The standard reduction potentials of Zn and Ag in water at 298 K are, \[Z{{n}^{+2}}+2{{e}^{-}}Zn;\]  \[{{E}^{o}}=-0.76\,V\] and \[A{{g}^{+}}+{{e}^{-}}Ag;\]\[{{E}^{o}}=+0.80\,V\]. Which of the following reactions take place?

    A)  \[Z{{n}^{+2}}(aq)+2Ag(s)\xrightarrow{{}}2A{{g}^{+}}(aq)+Zn(s)\]

    B) \[Zn(s)+2A{{g}^{+}}(aq)\xrightarrow{{}}Z{{n}^{+2}}(aq)+2Ag(s)\]

    C)  \[Z{{n}^{+2}}(aq)+A{{g}^{+}}(aq)\xrightarrow{{}}Zn(s)+Ag(s)\]

    D)  \[Zn(s)+Ag(s)\xrightarrow{{}}Z{{n}^{+2}}(aq)+A{{g}^{+}}(aq)\]

    Correct Answer: B

    Solution :

    As the reduction potential of Zn is less than that of Ag, hence Zn will act as anode when a cell is made using them. Hence the correct cell reaction will be               \[Zn(s)\xrightarrow{{}}Z{{n}^{2+}}(aq)+2{{e}^{-}}\] (oxidation)                 \[2A{{g}^{+}}(aq)+2{{e}^{-}}\xrightarrow{{}}2Ag(s)\]    \[Zn(s)+2A{{g}^{+}}(aq)\xrightarrow{{}}Z{{n}^{2+}}(aq)+2Ag(s)\]


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