Which requires the smallest voltage for electrolytic deposition given the reactivity order:

Question

Na> Al > Zn > Fe > Cu

1) Na

2) Al3

3) Fe2

4) Zn2

5) Cu2

Answer 1

Cu2+ will require the least voltage as Cu is the least active of these metals - you can also look up the reduction potentials.

Basically, by saying that copper is the least active of these metals, you are saying that it takes the most energy to oxidize the metal, and thus the least energy to reduce it.  Voltage is a measure of electric potential, or energy per unit charge.  Thus, a given number of Cu2+ atoms will require less energy to deposit (a reduction) than will the atoms of the other metals.  The number of other atoms to compare to is the number that requires the same number of electrons (same charge) as that for the Cu2+...