Thoughts on the Chemistry Bit (part 3) Y4

The previous blog was entitled ‘Thoughts on the Chemistry Bit (part 2) Y3 & 4’. Those with keen eyes – or at least those still awake – will have noticed that there wasn’t much on Y 4. This is because I  got a bit carried with the whole Y 3 thing and ran out of space/ energy/ will to live etc.

Anyway Y4 comes now and at first glance this looks familiar and OK. It is the part on solids liquids and gases and changes of state. Quite reasonably, there is also a look at evaporation and condensation as part of the water cycle. The notes and guidance have some reasonable ideas including a welcome reference to literature (chocolate factories get a specific mention – I think we could be thinking Golden Tickets and Charlie here) but they don’t bring out the differences and similarities between boiling and evaporation. It can be quite disturbing for a child who is taught that when a liquid changes to a gas the process is called boiling but a couple of weeks later is told to call the same process evaporation. (Boiling – liquid turns to gas but it happens all through the liquid, at one temperature: Evaporation – liquid turns to gas but it happens at the surface and over a range of temperatures). It would have been useful to flag this up for teachers.

However …( yes, you knew there would be a however) …. there are two statements in the PoS which will be somewhat tricky to do. ‘Explain that some materials change state when they are heated or cooled, and measure the temperature at which this happens in degrees Celsius’ and ‘Compare and give reasons based on measurements, for changes to the state of water, using correct scientific vocabulary’. Now I suspect that all they want here is for children to say that water melts at 0°C and that it boils at 100°Cm but the PoS stresses repeatedly that measurements are important. And, yes, measurements are absolutely vital in science but there are a couple of points about using them here. First our normal tap water does not do what it’s supposed to in this respect – it will be somewhere near those temperatures but because of impurities/pressure/vessel it is in etc. it won’t be exactly right and is usually out by quite a bit. (If you don’t believe me have a look at this paper  where a Prof goes on at some exasperated length about the way the boiling point of water can vary and his frustration at the way the ‘myth’ of 100°C is perpetuated.) Now, if children are taking those measurements, and don’t forget in Working Scientifically there is that line that says that everything we do must lead to substantive scientific knowledge’ I suspect many teachers will say to the children ‘your measurements are wrong’ and the ‘correct’ science is the one you need to believe i.e. don’t believe your own evidence just believe what I tell you.

Second there are a few practical issues here – putting a normal thermometer in a block of ice is a tad tricky so we have to start with crushed ice – that is fine – but heating it up to 100°C with the children taking measurements is fine in a properly equipped prep school lab, but could be a bit tricky safety-wise in your average primary school. Suppose we manage to deal with all that we now have the interesting issue of how we tell the boiling and the melting point of each liquid. Do you take the temperature when the first bit of crushed ice melts or the last or somewhere in the middle? And when do you know it is boiling? Plenty of steam/water vapour will be visible before boiling so just when do you say you have reached the boiling point? The only way you can really tell what these points are by plotting the graph and seeing where the graph goes flat. Now if I am 8 or 9 and I am plotting the line graph (which I won’t have met in maths yet – comes in at Y6 – but we’ll gloss over that one because I don’t really think that was what was intended) I will be very perplexed/interested/downright curious as to why when I am heating up the crushed ice so it melts and I continue to heat it up, never removing the heat source, it stays at the same temperature. If I have half an ounce of questioning left in me I will ask what on earth is going on. Now where do we go? Not I think into the following – temperature is a measure of how much particles are moving and that when the temperature increases the particles move more but that during a change of state the bonds between the particles need to be broken down and so the extra energy from increased heat goes into that rather than into more movement between the particles. Nah – don’t think that will help.

So we are left with an approach where children are told the melting point and boiling point of water and then they heat it up and dutifully take measurements. The teacher will say ‘Does your thermometer read 0°C – ah well it must be melting. Does it read 100°C – now that’s your boiling point.’  Starting from a known outcome and confirming it through a prescribed and predetermined route. No thinking required from the children. No using the evidence to work things out for themselves.  No proper science.


About annegoldsworthy

Primary Science specialist. Going for more independent thinking and less being told what to think. And that goes for teachers as well as children. We need to change that draft curriculum for science. Follow me on twitter @afgoldsworthy
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