How can a student best keep up with what is reduced and what is oxidized in a given equation?

Answer 1

To piggy back off Walt's answer, I prefer the acronym OIL RIG.

Oxidation

Is

Loss of Electrons

Reduction

Is

Gain of Electrons

Answer 2

To do this, you MUST be able to assign oxidation numbers to the different elements that are present. Once you are able to do this, you then see which element changes oxidation number in going from the left side of the equation to the right side. If the oxidation number increases (loss of electrons), that element is being oxidized. If the oxidation number of an element decreases (gain of electrons), that element is being reduced. Here is just one simple example:

Cu²⁺ + Mg ==> Cu + Mg²⁺

Cu goes from oxidation number 2+ on the left to oxidation number zero on the right. The oxidation number decreased so the Cu has been reduced (gained 2 electrons). The oxidation number for Mg goes from zero on the left, to 2+ on the right, so it has increased meaning it has been oxidized (lost 2 electrons).

Hope this makes sense.

Answer 3

A simple way to remember this is the acronym LEO says GER:

1. LEO: Loss of Electrons is Oxidation
2. GER: Gain of Electrons is Reduction