How do you figure which species would be the strongest oxidizing agent

Question

Fe3 e- -> Fe2 .771V

Cu2 2e- -> Cu .337V

Sn2 2e- -> Sn .140 V

I know the answer would be Fe3 but i dont know why

Answer 1

One way of looking at 'voltage' is to think of it as how strongly something wants to make electrons move. The higher the voltage, the greater is the force driving the movement of electrons in a circuit. (In electronics we call this the 'electromotive force'). If you look at it this way it becomes very obvious that in a given a list of voltages (or oxidation potentials) such as the one you have provided, the one with the highest value wants to drive the movement of electrons the most. Since the LOSS of electrons is oxidation, you can easily see that  the change of Fe3+ to Fe2+ has the strongest ability to take electrons away from something (that is, of oxidizing something).

It is easy to confuse what gets oxidized and what does the oxidizing, so make sure you take great pains to keep these straight.