So, a short and sweet post about one of my favourite low tech demonstrations for redox – I don’t even know what it is called, and I learned it from the fabulous Murray Vickers who was my associate teacher when I was a trainee teacher 10 (oh my goodness 10!!) years ago. It is a really nice demonstration as it shows not just the reaction occurring, but can be linked back to the composition of the air we breathe and the different amounts of gas.
All you need to do is get some steel wool, and put it in the bottom of a longish thinish tube. I used a gas jar this time, but a measuring cylinder also works well. You then need to put some water in the tube, so that when you upend it, and stand it in a container of water, there is still some water in the tube. The pictures below show it much better than me trying to write it out. But you need just a little bit of water in the tube. I put a line around where the water level was at the start
The gear was then left over the weekend, and as the oxygen was used up the water rose up the gas jar.
And as you can see, the water has stopped about 20% of the way up. Because Nitrogen makes up almost 80% of the ‘air’, and oxygen is just over 20%, the reaction will have stopped/slowed because there is no oxygen left to react with the Fe (iron) in the steal wool.
Often reactions with gases are hard to visualise – we also burned steal wool (makes great wee sparks) and you can’t really ‘see’ the oxygen being reacted. In this cause, you still can’t ‘see’ it, but you can see that something has happened to the gases.