When magnesium is heated in air, it reacts with oxygen. During this oxidation reaction, magnesium oxide is produced. This increases the mass. If we know the mass of magnesium at the start, and the mass of magnesium oxide produced at the end, we can work out the mass of oxygen which has been combined with the magnesium. We can use these masses to work out the formula of magnesium oxide.
Eye protection must be worn
Crucible and lid
10cm length of magnesium ribbon
Small piece of sandpaper
Weigh the empty crucible with its lid, and write down the result in a table.
Clean the piece of magnesium ribbon with sandpaper, then coil it loosely around a pencil.
Put the magnesium ribbon into the crucible and put the lid on.
Weigh the crucible, lid, and magnesium together, and write down the result in your table.
Put the crucible onto the pipe-clay triangle. Leave the lid slightly ajar to to allow air into the crucible. Heat gently for a minute, then strongly. Continue heating until the reaction has finished
(the magnesium will glow at first, then look a bit like a furry grey-black caterpillar – it really will!)
Turn the Bunsen burner off, and allow the crucible to cool for a few minutes.
Reweigh the crucible with its lid and contents, and write down the result in your table.
Results (suggested table only – do not write on this sheet) crucible Objects crucible + lid crucible + lid + magnesium crucible + lid + contents after reaction
pipe-clay triangle tripod
Work out the mass of magnesium used in the experiment.
Apparatus to oxidise magnesium
Work out the mass of magnesium oxide formed.
Use your answers to (1) and (2) to work out the mass of oxygen gained.
Look up Ar(Mg) and Ar(O). Use these