First slide
Nernst Equation
Question

For the following cell Zn / Zn2+// Cd2+/ Cd        Ecell = 0.30V and E0cell = 0.36V. Then the value of [Cd2+] / [Zn2+] is

Easy
Solution

Cell reaction

Z{n_{\left( s \right)}} + Cd_{\left( {aq} \right)}^{ + 2} \rightleftharpoons Zn_{\left( {aq} \right)}^{ + 2} + C{d_{\left( s \right)}}

Applying Nernst equation

{E_{cell}} = E_{cell}^o + \frac{{0.0591}}{2}\log \frac{{\left[ {C{d^{ + 2}}} \right]}}{{\left[ {Z{n^{ + 2}}} \right]}}

0.3 = 0.36 + \frac{{0.0591}}{2}\log \frac{{\left[ {C{d^{ + 2}}} \right]}}{{\left[ {Z{n^{ + 2}}} \right]}}

\frac{{ - 0.06 \times 2}}{{0.06}} = \log \frac{{\left[ {C{d^{ + 2}}} \right]}}{{\left[ {Z{n^{ + 2}}} \right]}}

\frac{{\left[ {C{d^{ + 2}}} \right]}}{{\left[ {Z{n^{ + 2}}} \right]}} = {10^{ - 2}}

 

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