“Blowing stuff up” in chemistry

The i-Biology blog writes a terrific response and meditation on the film in our previous post, and also includes this wonderful rant about chemistry demonstrations:

I think chemists have it tough when it comes to demos. Tougher than physicists, but in an odd way tougher than biologists too. Sure, there are precious few well-known biology demos (a subject for future posts, I’m sure), but chemistry is… hmm.

Look, I did a year of degree-level chemistry. I loved IR spectrometers. The only proper research paper to which I contributed was in computational chemistry. But I never really “got” chemistry. I never found that the practical work I did gave me confidence in the models I’d been taught, in part because of the bizarre ‘atomic model of the week’ strategy of late-80s A-levels. You know, the one where you’d just got comfortable with one particular version of How The World Works, only to have it pulled out from under your feet and replaced with something even more implausible. I found my eventual introduction to quantum mechanics a blessed relief, but then I’m weird.

My point is: I love chemistry demonstrations as theatre, but I’m squarely in the camp of not being able to remember any of the chemistry involved. What I think of as a ‘good’ physics demo reinforces or challenges my understanding of the principle behind it, but I rarely find the same sense of satisfaction in chemistry demos.

Is that because I’m a physicist; because chemistry demos are often used inappropriately; or because chemistry is somehow different?

Answers on the back of a £50 note to the usual address. Oh, and do check out the post at iBiology.

9 thoughts on ““Blowing stuff up” in chemistry”

  1. I did a PhD in chemistry, I’m a science communicator and I hope to be a chemistry teacher in the not-too-distant future and I have a confession. Not only do I agree that ‘blowing stuff up’ demonstrations are generally poor pedagogy and often pure pseudoteaching, I don’t even like them very much. I am a chemist and I don’t like blowing stuff up. There, I said it. I followed my love of chemistry DESPITE the practicals and demonstrations. Only in the 3rd year of my degree did I experience a practical which I actually enjoyed and which clarified the theory I’d been learning and that’s because it hadn’t been very well planned so didn’t work brilliantly. My colleagues and I had to find a better method to achieve our aim. We were actually doing chemistry for the first time. It was better than several hours of lectures or individual study and really did help my understanding. But it was the first time I’d had that experience, I’d pushed through every other demo and practical which had been thrust at me by holding onto the joy of the chemistry problem solved on paper which I kept hoping would be mirrored in the lab. I’m glad I held out so long, I loved every minute of my PhD (even the minutes awake at 4am at a synchrotron getting no data) but I feel sad that many other people who would surely have loved chemistry research just as much may not have been prepared to hold out so long when faced with teachers imitating vacuous and distracting magicians instead of honestly sharing the marvelous, complicated brilliance that is chemistry.

  2. Chemistry teacher who hated labs at uni. Worked in a lab then taught. Love blowing stuff up. Don’t like proper practicals. Useful for skills, not for theory.

  3. Is some of the problem that chemisty is really complex, if it wasn’t it would be physics. Historically, to a large extent, the dividing line between the two was that if you could do it properly with maths it was physics, if it was a bit woolley and you had to use more intuition then it was chemistry.

    Obviously modern chemistry is very much more quantative and a lot less woolley, but only by doing a lot of very abstract theory, and you need big chunks of theory which you don’t do until undergrad to understand most chemistry demos (which aren’t essentially physics).

    The theory which you are taught at school is the 19th and earth 20th century stuff which doesn’t work very well, and is still pretty abstract, so the demos don’t really work well. Whereas because physics concentrates on doing the ‘simple stuff’ if you go back to the 16th, 17th, 18th and 19th centuries there are lots of demos which are neatly explained by relatively simple theories, where as at this point the chemists had the demos but couldn’t really explain them.

    Of course the other issue is that chemistry is probably still more important economically than physics, which means that it has a lot of the properties of engineering, in that there are sections which are very important economically so you have to teach them, whether they make neat educational sense or not. Engineers will learn a lot of simplified tables for the properties of soils or beams which might not be entirely rigorous, but they stop buildings falling over, where as a physics course wouldn’t put that sort of thing in as it isn’t really ‘proper’.

    The other problem is just the practicalities, because liquids and powders are hard to deal with, it is harder to engineer the dull irrelevent bits out of a chemistry practical. A physics practical has a lot more of the conditions built into the kit (as it isn’t general purpose) where as in chemistry you have to put them in by following the instructions.

    Saying all of that both chemistry practicals and demos are far easier than museum exhibits…

  4. I run a young kids (age 9 – 11) science club, and found the rant on demos interesting and understandable, but in the end missing the point.

    Why do we do demos? Because it is not practical for the children (even older ones) to do the experiment themselves – demos in this case are a proxy for doing the experiment yourself (as is watching a video, or reading a text book, each of greater proxy-ness). But we also do demos to encourage – a real advantage that science, particularly chemistry, has over other many subjects.

    I don’t run the club to teach, but to enthuse. But learning usually follows I have found. The kids do everything unless it really is too risky (conc. acid on zinc), or when having and storing enough sets of kit for them all to do it costs too much or takes up too much room in my shed. The kids always ask if they are going to blow something up this session, and I say yes, but not today – we will do at the last session (when they each get to explode gun cotton on their hands). They are quite happy, and at the end of the year when I ask what they liked best, it is rarely the explosion session.

    So in my view, it really is doing it themselves that not only helps learning, but makes them curious and therefore want to understand. Once they do it themselves, then they start to ask questions – why does that happen, why does it do this, what happens if I… Then they are ready for an answer – to learn. In my gases session, we always do the raisins bouncing in fizzy water experiment (an experiment I lost interest in ages ago personally), but without fail they think it fantastic. Having got the raisins to bounce, they want to know why. What is happening? So we have a chat about what a gas is, carbon dioxide is a gas, what dissolving is, raisin catalysis, why some work and not others, what bubbles are, why they rise, why burping a fizzy drink can make your nose hurt etc. etc. etc. You really do learn from asking ‘what would happen if I…’, then doing it and finding out, and then trying to work out/understand why. Demos can only ever be a proxy – necessitated by practicalities, cost, fear etc.

    Michael’s do it quick, do it properly, approach is right. I do a quick demo, then the kids ‘do it properly’, themselves. It works. To quote one particular child “I liked the way that it was explained clearly, you learn new facts, there were experiments and it was all fun at the same time”.

  5. I do agree with this to some extent: sometimes teaching can turn into entertainment. Pupils will remember the result, not the reasons for it; the explosion, but not its explanation. They will go through the motions of doing practicals without necessarily learning very much. Many practicals that are rolled out in school science aren’t that great for understanding the science.

    One thing I always hate to see in science lessons is the kind of practical that the teacher does in its entirety, and then the students spend 30 mins doing exactly the same thing in smaller groups or individually. If you must demonstrate it first, do, but leave the actual doing of the interesting bit for the pupils to discover. (I often model how to use the equipment, but don’t actually mix any chemicals together – “…and I’m not going to do that bit, as I want you to find out what happens…”)

    I also think however that practicals and especially demonstrations (and there may be a distinction here) can be engaging and educationally valuable. The last Royal Institution Christmas lectures (given by Dr Peter Wothers) were an excellent example. I enjoyed them enormously, I was entertained and feel that I learnt something along the way.

    It’s very easy to become activity focused rather than outcome focused in teaching, i.e. you are forever thinking when planning about “what to do” in lessons – the activities, how to fill / use up the time – rather than starting with the question “where should the students get to?”, and planning the teaching/learning around that – a kind of “backwards design” process in which each activity is chosen only for its usefulness in attaining the desired outcomes (and practicals often aren’t the most productive use of time in this kind of assessment).

    There is no question though that practicals are a good way to fill time, and keep the pupils engaged (not misbehaving?) and everyone feels at the end as though the lesson is a success. Is this a problem? Well, for a start teaching can’t happen without engagement. Pupils can learn things without realizing it, without it feeling like learning, and whilst having fun: there is such a thing as “edutainment”. So long as the teacher doesn’t overestimate the usefulness of practicals, or kid themselves into thinking that learning has been going on rather than “pseudo-learning”, they could be a useful way to increase engagement, perhaps in other activities which will be more productive in developing understanding.

    In my first couple of years of teaching science, I confess to not all of the practicals I have done being the best use of time for learning (yes I do sometimes do a gratuitous explosion or a fun practical which I know has little or no benefit in terms of pupils’ understanding). But teaching is (dare I say it?) not just about maximizing the quantity learnt at the end of each lesson. There is more to it – building up a relationship with a class, helping them to experience success in your subject (completing a practical and getting the “right” result, perhaps), managing the classroom so that it is a positive learning environment (where people are engaged), rewarding pupils for effort, engendering a positive view of science.

    For all of these things, practicals and demonstrations are a useful tool in a science teacher’s arsenal, so long as the teacher is honest and reflective with themselves about the reasons for doing them, and realistic about their effectiveness. Science teachers (who have all been trained in using an evidence-based approach) should be well placed to assess this and make informed choices when planning their teaching.

  6. I have been thinking about the physics vs. chemistry demos question. In the kids club I run, the experiments tend to be more chemistry than anything else. Partly because I am a chemist and partly because you can get a ‘result’ very quickly, so I can get 6 – 8 experiments in a 2 hours session.

    Biology experiments tend to take a long time (and those we do we ‘start going’ first thing and hope they get there by the end of the 2 hours, for example food dye in flowers) and physics experiments tend to be about setting something up and then measuring something and so are sensitive to the ability to ‘set up’ well, (for example electricity from lemons). Chemistry experiments tend to be about transformations and are generally less sensitive to the setting up than the physics ones. In a demonstration situation, you can do the ‘here’s one I started going earlier’ option for biology demos, and you can pre-set up the equipment for the physics ones. Both physics and chemistry demos can be spectacular (or not), so I don’t really think there is a difference in terms of demos.

    I do agree with the previous comment though about developing a relationship with your students, and of not demoing the whole thing. I have found that ‘arching’ the level of excitement and effort works well; first experiment – I show all and is easy and gives a great result, second and third are the ones that they need to work at, possibly less ‘spectacular’, but they don’t know what will happen, then easier ones as they tire (and I do too), and always finishing with the ‘best’ one, even if it takes effort.

    I do think though that we hugely underestimate the value of simply doing. Of handling equipment, materials, knives, ice, chemicals, fire etc. Modern children have usually never been able to play with fire (possibly part of the demand to blow things up), never done any chemical reaction at home, or never even put a packet of mentoes in a bottle of coke (well it makes a mess doesn’t it). Rather than just watching or reading, they need to do, by themselves.

    1. I would have exactly the opposite feeling about the relative time between a physics and chemistry experiment. Chemistry experiments require lots of careful handing and measuring, where as with physics it is just taking a piece of kit and using it. Though that might me because I am a physicist…

      If you haven’t found it already


      may be useful for demos/practicals for a club context – there are a lot there and some of the nicer things are further back. It is rather physics dominated, as that is easier to do at home, and I am a physicist.

      I think you are right about the learning by doing being different from other forms of learning. It is slower, very hard to test in exams, but to actually do things (rather than just become a bureaucrat) it is vital, though most powerful with a theoretical foundation.

  7. At the heart of all chemistry demonstrations there is the Pauli exclusion principle.
    Demonstration do grab the attention and I used to love actually making salt when I explained bonding.
    However I must agree that when I did the wine into water demonstration I did not know any of the chemical reactions


    I do believe students should see these reaction and demonstrations

  8. How about you take the time to turn your water off every now and again. You just left it running THE entire friggin’ time!! I’m a chem teacher, but I have a stronger background in environmental science and you have no idea how hard I want to rant at you after watching this!!!! It takes two seconds to be responsible and turn the water off!!!! Hopefully your kids didn’t learn anything from THIS demonstration!

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