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A galvanic cell with a copper/copper sulphate half-cell and a zinc/zinc sulphate half-cell was used.

The concentration of the copper sulphate solution was kept at 1M. The zinc sulphate concentration was changed to variations of 1M, 0.8M, 0.6M, 0.4M and 0.2M. According to the Nernst equation, we expected that, as the concentration of zinc sulphate decreased, the voltage reading would increase.

These were the results:

Zinc Sulphate Concentration (M)
1.0 = 1.068
0.8 = 1.060
0.6 = 1.054
0.4 = 1.047
0.2 = 1.040

The results show that as the concentration of zinc sulphate decreased, so did the voltage. However, according to the Nernst equation, the voltage should have decreased as the concentration of the zinc increased. Can you explain why these results do not show the correct trend?

[Borek]

Have you kept ionic strength of the solution constant, or was it changing?