Burning Magnesium

Burning magnesium in a crucible is a great experiment for explaining several concepts:

• differences between elements and compounds
• conservation of mass
• stoichiometry

 Setting up the experiment is simple: Bunsen burner, heat-proof mat, tripod, clay-pipe triangle, crucible and lid, a strip of magnesium.

Weigh the magnesium before burning.

Weigh the lid and crucible empty.

 

 Coil up the magnesium and place it in the crucible.

Heat the magnesium in the crucible. Keep the lid on lifting only periodically to allow more oxygen in. Keeping the lid off for too long will lead to loss of material. Stop heating when the magnesium oxide stops glowing.

You can tell magnesium oxide has been formed due to the colour change: silver to white. You can also tell by the increase in mass.

Using the symbol equation you can deduce the stoichiometry (mole ratios) and hence how much magnesium oxide you should make.

 

Therefore if you use 24g of magnesium, you should make 40g of magnesium oxide. If you use 1g of magnesium instead then you can deduced the mass of magnesium oxide made by doing 1/24 x 40.

 

I usually get my students to compare the mass of magnesium oxide they made with the mass they should have made and then take it as a percentage.

 

All in all, a very useful experiment for teaching.  



Viruses!

Recently a class of mine modelled some viruses. Here they are in all their glory. You really wouldn't want to catch any of these. Sorry about the poor lighting.

Structure of the Atom

The structure of the atom is one of my favourite lessons because it is so important: it underlies all other Chemistry.

Atoms are so small that it's difficult to understand them. This interactive animation (click here) helps you to visualise their size. When it loads. Scroll to the left to see their size.

Lesson summary:

Parts of the atom

This is the Bohr model of the atom. At GCSE, this is a good model to use.

Note that protons and neutrons are in the nucleus. Electrons orbit the nucleus and are in shells or orbitals (or energy levels).

Protons have a positive charge. Neutrons have no charge. Electrons have no charge and are attracted to protons; opposites attract and like charges repel.

Sub-atomic particle	Relative Mass	Charge	Location
Proton	1	+1	In the nucleus
Neutron	1	0	In the nucleus
Electron	1/2000	-1	Orbiting the nucleus

 

Adding the number of protons and neutrons together gives you the atomic mass (or mass number) of an element.
Elements also have an atomic number which tell you the number of protons in an atom.
This diagram helps:

 

You can calculated the number of neutrons in an atom given the mass number and the atomic number and taking the difference between them.

E.g. Lithium  has atomic mass 7 and atomic number 3. Take the difference between these to get the number of neutrons, in this case, 4.

This video is a nice summary of the structure of the atom. Click here.