Does the salt bridge in a galvanic cell have to have the same ions as the ones in the solutions? E.g. does it need to have nitrate ions if the half-cells contain copper nitrate and zinc nitrate, or could nitrate ions still be used if the solutions had sulfate instead?

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    $\begingroup$ Any ions will move in the electric field. It is not that the ions in the cell would build a border wall against the ions of different kind and make them pay for it. It is just that the ions from the salt bridge would slowly get into the half-cells and vice versa. As long as this doesn't cause any unwanted reactions, it is not a big deal. $\endgroup$ – Ivan Neretin Feb 4 '19 at 16:12

In short: a priori no, it need not.

The purpose of the salt brigde is to close the electric circuit (transport of charges) between the two half-cells. To work as intended, all you need to do is to fill the bridge with any salt whose ions, both cation and anion do not react with either half cell components, nor under the external potential applied, and ideally have the same mobility in the electrolyte of the bridge, expressed by the transfer number. This is why aqueous solutions of KCl are used so often for this purpose, but you are free to choose differently.

And not to forget, the tube normally ends by a diaphragm at each side, to slow down considerbly the mechanical exchange of matter (ions) between the bridge's content and the half cells.

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