[silverks]

Hi,

I was running a voltaic cell experiment, and decided to test on the effect of the surface areas of the metals to the current produced. I use Daniell Cell for this experiment with the following voltaic cell:
Zn / Zn²⁺ || Cu²⁺ / Cu

Under standard condition (1M ZnSO₄ and CuSO₄ salt solutions, saturated KNO₃ as salt bridge), the cell registered a voltage of close 1.10V, which is the expected voltage. I choose to vary the sizes of the metal and test the effect of surface area to the current produced by this cell. Both current and voltage produced are measured by using an electronic multimeter with precision to 0.01 mA and 0.01 mV respectively.

My hypothesis is that the voltage would not change, but the current produced will increase as the surface area increase. This could be explained by the increased amount of Zn metal being oxidised to Zn²⁺ and Cu²⁺ ions being reduced to Cu metal as the surface area increase. As a result, more electrons will be transferred at any given time and hence the increase in current. However, the results of this experiment surprises me.

As I increase the size of both metals dipped inside its salt solution, the current decreases. This puzzles me and I don't know how to explain this observation. It goes against the hypothesis and I have no explanation for it. I need help.

Five sizes are used for both Cu and Zn metal in this experiment, which are (5 x 1) cm, (5 x 2) cm, (5 x 3) cm, (5 x 4) cm, and (5 x 5) cm. This whole experiment is repeated for several times to ensure no critical flaw is involved in the experiment, but all repetitions produced the same results. My chemistry teacher did the same experiment too and produced the same result. He couldn't explain the results as well.

Initially, the sizes of both metals are increased. Puzzled over the results, my teacher ran another experiment but this time, by fixing the size of one metal and increasing the other. When he fixed the size of the Cu metal and changes the size of Zn metal, the current drops as the size increases. However, interestingly and yet still puzzling, when he fixed the size of the Zn metal and changes the size of the Cu metal, the current increases as the size increases. I repeated this experiment and confirm his findings.

Anyone who have any idea on how to explain this results, please do reply.

Note that for all experiments, five sets of data are obtained and the increase/decrease pattern persists for all data sets.

Thanks.