What are some common mistakes students make with galvanic cells?
This is a topic I have found most students seem to grasp without too much difficulty. A few common errors they make are listed below...
If you give the setup of the cell, they sometimes get the operation backwards. That is, they mix up the anode and cathode, and so, get the half-reactions switched. This is by far the most common error.
If one electrode is a metal that can oxidize into two or more forms (such as Fe or Cu), they have difficulty judging what the product of the oxidation will be, and as a result, get the wrong cell potential.
Finally, they can find it difficult to determine the reduction that occurs in the case of an inert electrode like platinum, where the product of the reduction is not the material of which the cathode is made.
These are the areas in which I have found students have the most difficulty. (I have taught this topic at high school level for almost 30 years.)