Unexpected learning through a Predict-Observe-Explain (POE)

I had a wonderful experience in one of my lab classes just the other week.  We were doing the second of two experiments looking at understanding some types of reactions and putting together some solubility rules.  One particular group of students had an unexpected result, in that they noticed bubbles in one of their test tubes when they weren’t expecting it. (Nor was I for that matter!)

So, having learned a little something about putting together a Predict-Observe-Explain (POE) demonstration in my teaching classes, I tried to do a little impromptu learning with them.  Things were rolling smoothly, they were asking insightful questions and making useful and sensible suggestions about how we could work out what the bubbles were.  We did some more test tube reactions that seemed to contradict their initial predictions, and they managed (with gentle guidance and suggestion) to work out what may have been really going on.  Most importantly, they were really interested to work it out and were really proud of themselves in the end – and so was I!

The only downside was that it was a completely unexpected reaction that shouldn’t have occurred if the reactants were what they said they were – so we couldn’t get full closure on what happened. D’oh.

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3 responses to “Unexpected learning through a Predict-Observe-Explain (POE)

  1. Now I’m curious… What were the reactants?

    • I hadn’t wanted to go into too much detail, in case it got boring for the non-chem readers out there, but it was magnesium oxide reacting with 2M nitric acid. Theoretically it should’ve just dissolved in a neutralisation reaction, but it produced bubbles of (what we worked out to be) carbon dioxide – as if it was magnesium carbonate instead. They did a pop test and not only did the flame not produce the ‘pop’, but it was doused instead. So they worked out it couldn’t be hydrogen, but must be a gas that would put out a flame (so not oxygen either). The other interesting observation they made was that the smoke from the match was sinking inside the test tube – an unexpected sign of the more dense CO2. My only realistic explanations were that their test tubes were dirty or that the reactant was actually magnesium carbonate by mistake.

  2. Pingback: Turning things on its head | Chemistry Chris

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