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I have used zinc sulfate and copper sulfate as the solutions, and used zinc and copper electrodes. For salt bridge I took lithium, potassium, calcium, sodium and zinc nitrates. The results are as below:

$$ \begin{array}{lr} \hline \text{Compound} & E_\mathrm{cell}/\pu{V} \\ \hline \ce{LiNO3} & 1.081 \\ \ce{NaNO3} & 1.057 \\ \ce{KNO3} & 1.071 \\ \ce{Ca(NO3)2} & 1.069 \\ \ce{Zn(NO3)2} & 1.071 \\ \hline \end{array} $$

As it shows, there is very insignificant difference. Is the results supposed to be like this or have I done something wrong in my experiment or something so that the voltage was constant?

If I have done something wrong, then should I have changed the anions instead of the cations? Or would it have been a mechanical problem?

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  • $\begingroup$ The voltage should not depend on the composition of the salt bridge. What were the concentrations of your solutions ? Were your measurements constant and stable in time ? Or were they slightly and slowly moving ? $\endgroup$ – Maurice Mar 3 at 16:56
  • $\begingroup$ @Maurice I took the same concentrations for all the solutions, and I made sure that my measurements were stable most of the times. Also, I have done many other trials as well, which all look like this. $\endgroup$ – Juhan Mar 4 at 10:51
  • $\begingroup$ How did you make your salt bridge ? With agar ? With another gel ? With a membrane ? $\endgroup$ – Maurice Mar 4 at 19:38
  • $\begingroup$ @Maurice my teacher told me to use filter paper. It wasn't like there was no current. $\endgroup$ – Juhan Mar 5 at 2:29
  • $\begingroup$ Well ! With a filter paper, you cannot prevent the anode and cathode solutions from intermixing. So the measured voltages are not reliable, because some copper ions can get into the zinc compartment. This will short the circuit, as the reaction $\ce{Zn + Cu^{2+}->Cu + Zn^{2+}}$ happens in the anode compartment and will not produce any current. A salt bridge must be made in such a way that only negative ions from the copper side can cross it, and no ions in the opposite direction. $\endgroup$ – Maurice Mar 5 at 9:16

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