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Along with others of late, including Kristy Turner , Niki Kaiser and Adam Boxer, I have been mulling misconceptions and teaching. Cognitive Load Theory is also being discussed a lot and I’ll be attending Niki’s conference soon to hash out some more on these ideas and how to apply it to the classroom. Much of what I have read resonates with my previous teaching, and I’ve written about it in relation to practical work.

What prompted this particular post was a session with Steve Barnes and David Read at the Wessex Group conference a couple of weeks back, and a Twitter chat recently. Both were related to aspects of equilibrium, a concept many students find hard, especially when questions are a bit different from what they have seen before. With the increased demand in the new A level papers, and the increased emphasis on applying knowledge to unknown situations, this seems like a timely issue.

Eric Scerri noted a couple of years back the problems with Le Chatelier – it works sometimes, but can break down quite quickly, and can potentially stop us from having to think thinking too hard about the details of the context. Somewhat like Kristy’s SEABODI, students tend to go for a stock answer to the almost inevitable NH 3 or SO 3 production questions, but aren’t necessarily thinking deeply about their understanding.

At the Wessex Group conference, Steve used a set of equilibrium questions, drawing on work by Juan Quilez, to highlight these problems. We also discussed the nitrogen dioxide-dinitrogen tetroxide equilibrium. When applying Le Chatelier to this equilibrium, and looking at changing temperature, the expected changes to equilibrium position and hence observations are borne out, as seen in numerous videos. Increasing the pressure by compression is more complex. The expected shift in the position of equilibrium is to the right to decrease the pressure. A not uncommon prediction of the observation would be that the mixture lightens, as NO 2 is converted into N 2 O 4 . The problem is that as the total volume has decreased, the mixture actually darkens initially as the NO 2 becomes more concentrated, then the colour lightens as the NO 2 is converted to N 2 O 4 . So the shift in equilibrium position may be correctly predicted, but the predicted observation may be wrong (or at least incomplete) because the full system was not considered or the question is not carefully phrased.

I recognise that at times I have come to rely on shortcuts and when the questions becomes more complex, the shortcuts can break down. Now, Le Chatelier is model like any other – we tend to use the simplest model that will allow us to explain the observations. When the model breaks, we use or develop a more sophisticated one. This issue has tied up with other conversations recently on what is meant by ‘mastery’ in science – is it mastering the concepts at the appropriate level, or introducing more sophisticated concepts earlier on so we aren’t ‘lying’ to the students. I’m not sure it would be appropriate to introduce GCSE and / or A level models directly in KS3. I may be able to get the students to repeat back the facts, but I doubt they’d be able to use them confidently or competently. Of course, this is a whole bucket of worms on assessing understanding – for another time perhaps.

What finally prompted this post was a resource I was reviewing on fuel cells. I have always found electrochemistry one of the harder topics to teach effectively, and tend to take more of a pause before launching into it. I have taught electrolysis plenty at GCSE, but for whatever reason never really gone into galvanic cells and fuel cells in detail. I had developed shortcuts for electrolysis along the lines of ‘it’s the reverse of normal chemical reactions’ and ‘cathodes are negative as cations are attracted to them’. I got myself into a muddle with the hydrogen fuel cell, on working out the polarity of electrodes, not helped by some vaguely written resources. A quick shout out to Twitter set me straight (thanks to Peter Hoare and Adrian Dingle), but it was a useful reminder of the need to check my understanding of the fundamentals from time to time.

Does this have any wider relevance – certainly for me going back to teaching after a couple of years out. For others – perhaps. I think it points to the importance of subject knowledge CPD. I’m a strong advocate of pedagogical content knowledge CPD, but spending time on deepening my personal understanding of the content knowledge is probably worthwhile from time to time. At this point in my teaching career, I would put depth ahead of breadth now. I have sufficient breadth of chemistry to teach my students effectively at the level I’m teaching at, but I think increasing the depth of my understanding as the years pass can only be a good thing. There are some great resources out there. I’m a particular fan of knockhardy and chemguide. I also have a copy of Chemistry3 close by – I’ve consigned my other university books to the lab shelf – I think one general undergraduate chemistry text is sufficient for what I need for now.

Any thoughts? When was the last time a student asked you a question that you couldn’t quite answer to your satisfaction? What resources do you use the support your depth of understanding?