The tank over here is filled with carbon dioxide gas.
Now carbon dioxide is heavier than air.
Heavier than air, so this tank is filled with carbon dioxide
and it should put out a fire. So I'm going to put into this
some petrol, some cotton wool soaked in petrol set alight and it should be able to put it out.
Okay.
So here we are. Burning petrol into the carbon dioxide. And it's gone out.
Lets try again.
So carbon dioxide is heavier than air.
So it's staying in the tank but as soon as I put the burning petrol in it goes out.
Now could this be used to put out burning magnesium? Well let's try it.
So I have some magnesium here
and I'm going to set this on fire and see if we can put this out in the carbon dioxide.
So here we are, the magnesium is burning and lower it in to the carbon dioxide
and actually it's burning even more vigorously than it did before
and if I put in the burning petrol
it's still put out but I can't light my petrol on the magnesium.
So the petrol will not burn in the carbon dioxide but the magnesium will. Okay.
So carbon dioxide is very good for putting out fires that form
carbon dioxide or water but it's no good at putting out the magnesium.
Well what's happening here?
If I reach in and take this out, well we see a lot of smoke forming on the surface here,
this is magnesium oxide
and if we look at what's left
we see some white magnesium oxide but deep inside here
there's a lot of black and this black is carbon
that's been formed when the magnesium has stolen the oxygen from the carbon dioxide
so forming magnesium oxide and leaving behind carbon.
So we can show this with a chemical reaction, a chemical equation here.
So this has magnesium reacting with carbon dioxide, so
Mg is the magnesium, carbon dioxide reacts together to form magnesium oxide,
the magnesium steals the oxygen from the carbon dioxide
leaving behind the black carbon and also releasing energy so the magnesium burns
in the carbon dioxide. So we can't use carbon dioxide
to put out burning magnesium.