[777888]

A student makes 4 galvanic cells by having Cu as a electrode in each cell, and has the other electrode as Pb, Mg, Zn, Fe, respecctively. Each half-cell has its corresponding electrolyte. A salt bridge with KNO3 and a wire to the elctrodes are connected. The positive terminal of a voltmeter is put on the Cu and the negative terminal is put on Pb, Mg, Zn, Fe respectively to measure the voltage. He then arrange the cells in order from smallest to largest cell voltage. Why is the copper electrode always used?

I don't get this question... can somebody explain to me? I would appreciate!

[Donaldson Tan]

electrons flow from low to high potential. if you want electrons to flow from Pb/Mg/Zn/Fe electrode to another metal electrode, that electrode must be made of a metal that has a lower redox potential than Pb/Mg/Zn/Fe. Copper fulfills this condition.

[Demotivator]

Since the student is comparing the potential strengths of the other half cells, the comparisons should be made with reference to a constant, in this case the copper half cell.