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I am doing an experiment where I use salt bridge to create galvanic cell. The goal of my experiment is to find if there is some correlation between the amount of solvent being used and the voltage being produced which means the accuracy of voltage is very important.

I am using zinc and copper metal pieces, zinc sulfate, and copper(II) sulfate with sodium chloride for salt bridge:

Galvanic (Daniel) cell

The experiment works, but the problem appears that when I modify the position of either the metal piece or the salt bridge, the voltage value will change, sometimes I will change a lot (e.g. $\pu{0.3 V}$ to $\pu{0.42 V}).$

Does the change of the position of the salt bridge or metal piece leads to different voltage value in galvanic cell?

If not, could it be the reason that my zinc sulfate powder does not fully dissolve in water? So my metal piece could touch the area where there are more Zinc powder which causes it to be more electron transfers happens. It is very hard to get it fully dissolved in distilled water. Any suggestions for improving solubility in water?

I am really looking for way to reduce the uncertainty of my experiment, but the different voltage measured by only changes the salt bridge or metal pieces makes me very concerned.

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    $\begingroup$ (+1) for including the photograph! Moving things around can change the cell’s internal resistance, thereby changing the potential you measure. This is a Daniell cell, so there is no need for high zinc ion concentration and the liquid in the anode reservoir (beaker) should not be cloudy. $\endgroup$
    – Ed V
    Jan 11 at 19:33
  • $\begingroup$ @EdV, thanks for the comment. Do you have any suggestions for increasing accuracy of the experiment? I am doing an experiment where I keep adding water to the solution to record the voltage, but the different position of the salt bridge or the metal piece seems to result in different voltage value after the voltameter measured stop changing. $\endgroup$
    – James
    Jan 11 at 22:36
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    $\begingroup$ I am not surprised at all. Even if you just add solution (or remove some), you change both the cell resistance and the electrode contact area with the solutions. Even worse for adding water because the solution concentrations change. So you have multiple things influenced by the one factor you are controlling. Hate to say it, but you might need to redesign a bit to get an unambiguous relationship between what you control experimentally (solution volumes) and the cell’s open circuit (or lightly loaded) response voltage. As well, the Nernst equation always is pertinent. $\endgroup$
    – Ed V
    Jan 11 at 23:05
  • $\begingroup$ @EdV, thanks for that, so basically I am research if the amount of water has a relationship while making other condition be constant. My independent variable is the amount of water being used. I am wondering how do I have changed the cell resistance in the experiment? Do you mind explain it a little bit so that I could redesign the experiment. Sorry, I don't have too much knowledge with chemistry :( $\endgroup$
    – James
    Jan 11 at 23:25
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    $\begingroup$ Well, pure water is a poor electrical conductor because it has very low concentrations of ions. Your electrolyte solutions are much better electrical conductors: they have relatively high ionic content, so their electrical resistance is low. Diluting them lowers their ionic content, so their resistances increase. The cell output voltage is the net output after the voltage drop due to the cell resistance is deducted, as it were. So there are always trade offs and this is one such. Anyway, I will leave it to others to respond further. Best of success! $\endgroup$
    – Ed V
    Jan 11 at 23:38

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