JEE Main & Advanced Sample Paper JEE Main - Mock Test - 31

  • question_answer
    Given \[\operatorname{E}{{{}^\circ }_{C{{r}^{3+}}/Cr}}=-0.72V,\,\,E{}^\circ {{ }_{F{{e}^{2+}}/Fe}}=-\,0.42\,V\] The potential for the cell \[\operatorname{Cr}\left| C{{r}^{3+}}\left( 0.1\,M \right) \right|\left| F{{e}^{2+}}\,\left( 0.01\,M \right) \right|\] is

    A) 0.86 V

    B)                    0.336 V

    C) - 0.339 V          

    D)        0.26V

    Correct Answer: D

    Solution :

    From the given representation of the cell, \[{{E}_{cell}}\] can be found as follows. \[{{E}_{cell}}=\left( E_{F{{e}^{2+}}/Fe}^{{}^\circ }-E_{C{{r}^{3+}}/Cr}^{{}^\circ } \right)-\frac{0.059}{6}\log \frac{{{\left[ C{{r}^{3+}} \right]}^{2}}}{{{\left[ F{{e}^{2+}} \right]}^{3}}}\] \[\left[ Nernst\,Eqn. \right]\] \[=-\,0.42-(-\,0.72)-\frac{0.059}{6}\,\log \frac{{{(0.1)}^{2}}}{{{(0.01)}^{3}}}\] \[=-\,0.42\,\,+\,\,0.72-\frac{0.059}{6}\,\log \,\frac{0.1\times 0.1}{0.01\times 0.01\times 0.01}\] \[=0.3-\frac{0.059}{6}\log \frac{{{10}^{-2}}}{{{10}^{-6}}}=0.3-\frac{0.059}{6}\times 4\] \[=0.30-0.0393=0.26\,V\]


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