OIL RIG – does it cause more harm than good?

There are some things that have just been so ingrained into my teaching practice that I stopped questioning them.

oil rig

“Oxidation is loss, reduction is gain”. What is not to like? It’s plastered over every almost every GCSE and A Level chemistry textbook and revision guide on my shelf. And yet, it’s only this year – having had to teach redox to tutees from different schools and also to several GCSE and A Level classes, I started to really question the logic.

While it scans beautifully and leads being able to put a lovely picture on the front of my redox booklets (with a sideways link to rusting and sacrificial anodes), I’m beginning to feel that it causes as many conceptual problems as it solves.

Images from various textbooks. Terrible photography my own.

Problem one – loss and gain of what?

This is the most obvious one in my mind. If a student needs to rely on a mnemonic, it should be a complete phrase. But we often use OIL RIG at the same time as giving the opposite definition with regards to oxygen. Add in the definition of oxidising agent and reducing agent in the same topic and it’s no wonder students end up confused.

Problem two – what does ‘lose’ mean?

Let’s face it – the word doesn’t describe well what actually happens to electrons in a redox reaction. It encourages the idea of electrons being flung off into space somehow – and does not help students differentiate between the half equations used to represent oxidation and the nuclear equations they learn in physics.

Sure, they look very different to me, but I know from teaching both that students don’t easily see the distinction.

Very few students I’ve ever spoken to have ever really equated the word ‘loss’ with electrons being on the product side of the half equation. So much so that a few years ago I resorted to a new ‘cheat’ for my students to differentiate between oxidation and reduction half equations. I split up the word Red][ox in two. Where are the electrons in the equation? Electrons on the left, reduction – electrons on the right, oxidation – just like the word redox.

Yes, I know – I’m part of the problem!

What language can we use instead?

Firstly, I would say that we are going to be stuck with the word ‘lose electrons’ for as long as this is what examiners require in mark schemes (like using ‘bromine water’ instead of ‘aqueous bromine’). So perhaps a better suggestion would be what language we can use alongside OIL RIG.

We use the word ‘product’ in chemistry from the very first moment we introduce reactions and equations – before most students have any concept of atomic structure or electrons. We talk about reactions that produce energy, produce gases, produce a precipitate, produce a certain mass of products or percentage yield. Why not produce electrons instead of losing them?

Well, yes, the obvious reason. ‘OIP’ is not a word.

Mnemonics are rarely perfect – not least because the word itself is so ridiculously hard to spell (is there a mnemonic for this?) – but this is what I came up with as my alternative:

OPERATE: oxidation produces electrons, reduction attaches to electrons

Feel free to improve it if you can – and let me know what you come up with! I’m less happy with the second half, but then if we know that oxidation and reduction are opposite processes then the second half of the phrase is only really window dressing.

It even lends itself to cute cartoons of surgeons extracting electrons from the outer shell of a magnesium atom. You are welcome, revision guide writers.

Teaching Redox at A Level

I actually found MORE references to OIL RIG in A Level textbooks than I did for GCSE – perhaps because they have to deal with half equations in so many less familiar contexts. But I do question why we need to keep referring to electron loss and gain once students have been introduced to the concept of oxidation number.

Oxidation defined as an increase in oxidation number works well in organic contexts, and it is surely not too much of a stretch for a student to realise that losing a negative particle will result in a more positive oxidation state. The idea of ‘producing electrons’ also helps to link the oxidation process with the negative electrode in electrochemical cells.

Disclaimer

So, have I actually stopped using OIL RIG and tried the new method? Er, no. I am now well past the half equation stage of teaching with all my classes – however I am slipping in the phrase ‘produces electrons’ as much as possible in my explanations. For what it’s worth as a completely uncontrolled experiment, it does seem to be helping my students visualise the direction of electron flow in both electrolysis and electrochemical cells. And since I’m teaching these topics over Zoom – I’ll take literally any win.

Claire Costello-Kelly

Claire Costello-Kelly

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