Which of the following combinations would require an electrolytic cell?

Question

coat aluminum onto iron

coat iron onto lead

coat copper onto tin

coat calcium onto iron

Please help.

Answer 1

Look at the activity series of metals. From most reactive to least it is as follows:
Ca, Al, Fe, Sn, Pb, Cu

http://www.files.chem.vt.edu/RVGS/ACT/notes/activity_series.html

Any METAL will displace the ION of a metal below it. For example,
Al + FeCl2 ==> AlCl3 + Fe (not balanced). Therefore, Fe plates out on Al spontaneously. You don't want that. You want Al to plate on Fe; that requires energy to do it and it requires an electrolytic cell.
Fe is above Pb; therefore, Fe will go in and Pb will come out which means Pb will plate onto Fe. Again, that isn't what you want; what you want will require an electrolytic cell also. Just go through the list.

Answer 2

I'm confused. I need help on this too. So in order for something to need an electroylytic cell, the one that plates onto the other has to be above the one it plates onto? Am I understanding this correctly?