#1. The galvanic cell above has equal volumes in the two halfcells. As it is discharged at 25 ºC, the cell potential gradually decreases to zero, whereupon the discharge stops. What is the concentration of Cu2+(aq) when the discharge stops?
The standard cell electrode potential is 0.36 – 0.337 = 0.023 V (note that we do not multiply 0.36 V by 2 because standard electrode potentials are intensive quantities). Let x = d[Cu2 ]. Using the Nernst equation,
0.023 = (RT/nF)ln([Cu2 ][Fe(CN)64-]2/[Fe(CN)63-]2)
0 = 0.023 – (8.314×298)/(2×96485)ln((1 x)[0.2 2x]2/[0.2-2x]2)
So, x = 0.041, and [Cu2 ] = 1 0.041 = 1.04 M.
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