Ways to Remember Oxidation and Reduction

One of the things that trips me up in chemistry is getting my head around which element is oxidised and which is reduced and which one is the oxidant and which one is the reductant in a redox reaction. They're not terribly difficult concepts really, but it's easy to get them mixed up. It's also pretty easy to get all mixed up between which process takes place at which electrode when a substance is undergoing electrolysis. So here I'm going to compile as many different ways as I can think of as remembering which one is which. Having a variety of different methods might just make you more confused, though, so read on with caution!

If you have absolutely no clue what I'm talking about, then look at my pages on redox equations and electrolysis.

Anyway. Here we go with all the mnemonics and whatnot:

AN OIL RIG CAT

This is probably the one you'd have been taught in your Chem class. OIL stands for Oxidation is Loss [of electrons], and RIG stands for Reduction is Gain [of electrons]. So, to find out whether something is being oxidised or reduced, just work out of the substance is losing or gaining electrons and then apply this mnemonic. Another nifty thing this mnemonic does is it helps you remember where oxidation and reduction takes place in electrolytic cells or whatever they're called. You see, AN stands for anode, and it's where Oxidation (which Is Loss) takes place. CAT stands for cathode, and it comes directly after RIG as the cathode is where Reduction (which Is Gain) takes place.

Reduction = Reduced [oxidation number]

This is the way I remember it. A substance is being reduced if its oxidation number is reduced. A substance is being oxidised if its oxidisation number is increasing (higher oxidation number = more oxidation?). Then you just have to remember that the reducing agent is the thing being oxidised and vice versa. (I find that once I work out what's being oxidised and reduced, it's much easier to work out the oxidant and reductant.)

Cathode = Cations

One way that I remember that stuff gets reduced at the cathode is that cations (positive ions) go to the cathode. Since the ions are already positive, they'd probably be wanting to gain electrons, meaning that there's a reduction taking place. Similar reasoning can be applied for the anode: anions (negative ions) go to the anode, and they probably would be wanting to lose some electrons rather than gain them. Hence oxidation takes place at the anode.