Number 22: Burning steel

What do you need to make stuff burn? Just three things, oxygen, a energy source to get it all started and some fuel. These three things are there every time you light a candle or start the engine of a car. The candle wax (or petrol) is the fuel, the match (or a spark) gets is all started and the whole thing is kept going with the oxygen in the air.


So what else can we get to burn? How about steel?

Steel is mostly iron mixed with some carbon and sometimes, other metals (depending on what the steel will be used for) and its not something you'd normally think burns.

You'll need

• Steelwool
• 9 Volt Battery
• Some old tiles or something similar that you don't mind getting scorched. 

Safety

This reaction generates a lot of heat (chemists call it an exothermic reaction) and can throw out sparks so make sure there is nothing near by that might catch fire. Have a bucket of water or fire extinguisher handy.  You can also end up with some small particles of steel wool being chucked up and you don't want to get them in your eyes, so wear safety goggles. Make sure there is a responsible adult supervising. Finally, because you get some smoke and sparks produced you should do this outside, you don't want to set fire to the kitchen.

What to do:

1. Fluff up the steel wool a bit. This is to make sure there is plenty of air in amongst it all.
2. Put the wool on the tiles (or whatever it it you are using)

3. Touch the terminals of the battery to the wool.

Almost instantly you'll see part of the wool glowing red hot, very quickly this spreads through the whole clump of wool, consuming it all. Like this:

What's going on:

When you burn things with carbon in them (these are known as organic compounds), like candle wax or fuel in the car, you are reacting the carbon with oxygen to make carbon dioxide gas (which has the chemical formula CO₂ meaning 1 carbon and 2 oxygens). But in this case there isn't any carbon to burn nor are we lighting anything with a flame. Instead the electricity from the battery runs through the steel wool and heats it up. This happens because the electrons and ions that form the electricity collide with other particles that make up the steel wool making them move around, and heat is just the result of particles (like atoms) moving.

The heat speeds up the reaction between the iron in the wool and the oxygen in the air. This would happen anyway, without your help, just much slower (that's why things rust). And this reaction produces heat (its exothermic) which kept the reaction going until you run our of fuel (i.e. the steel wool).

When you burn candles or wood you don't end up with much left over. That's because carbon dioxide is a gas, so it floats away. But when you burn steel wool you end up with iron oxide which is a solid, hence the black stuff that's left over. One more thing,  the chemical formula the iron oxide is Fe₂O₃ ie. 2 iron atoms (which have the chemical symbol Fe) react with 3 oxygens.