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.

 

Pyrotechnics

Disclaimer: I am a qualified and experienced Chemistry Teacher; I have done these demonstrations many times and I know what I am doing. I have also done a thorough risk assessment. Please don't try to copy me.

That aside, I hope you enjoy these videos.

1) Fireball on hand

2) Fireball with pure oxygen

Questions
1) (Key Stage 3) What are the energy transfers involved in a methane fireball?

2) (GCSE) Are the products identical when pure oxygen is used, compared to when the methane is ignited in the air only? Explain your answer (using equations if possible)

3) (A-level) An average methane fireball is 500dm³
a. How many moles of methane gas is this?
b. What mass of methane does this equate to?
c. How many moles of oxygen is required for complete combustion?
Show your working

Making an ester

Learning Objectives:

• To know the reactants needed to make an ester
• To be able to synthesise an ester

How to make an ester

Esters are aromatic chemicals, they have a smell.

Esters can be made to give different smells depending on what is used to make them.

Every ester is made from an alcohol and an acid

The acid used is a different acid to the catalyst which is concentrated sulphuric acid

We will use salicylic acid and ethanol to make an ester which is “Oil of Wintergreen”

 Method

·         Boil a beaker of water for a water bath

·         Take a boiling tube and add 5 cm depth of ethanol

·         Add a heaped spatula of salicylic acid (a powder)

·         See your teacher who will add some concentrated sulphuric acid (why is this?)

·         Place the boiling tube in your boiling water and remove the Bunsen burner (why do we remove the Bunsen burner?)

·         Leave in there for approx 10 mins

·         After 10 mins, pour the contents of the boiling tube into half a beaker of cold water

·         Smell it the oil which floats on top, but don’t go mental

 

This was my last lesson of the academic year with Year 9. A lovely class. I hope to teach them again.

Fireball on hand

A picture of me from a couple of years ago doing methane fireball. This happens quite often at the end of term - often whether I like it or not...

Solution X

Year 10 applied their knowledge of tests for anions and cations to discover the ions present in Solution X.

Solution X was a concoction of a metal salt solution, with other chemicals. It was a blue solution.

Test 1. 1 M sodium hydroxide solution was added to give a brown precipitate showing the presence of Iron (III)
Test 2. The addition of silver nitrate solution gave a white precipitate showing the presence of Chloride.
Test 3. Solution X turned blue litmus paper red: it was acidic and so contained Hydrogen ions
Test 4. Solution X was heated with aluminium foil and 1 M sodium hydroxide solution. The gas given off turned red litmus paper blue, because ammonia gas was released. Therefore the solution contained nitrate ions.

The class accomplished this fairy well, although surprisingly didn't all think to try test 3 given the starting equipment.

In the end every group identified the four ions and deduced I has mixed iron (III) chloride with nitric acid. However they couldn't account for the blue colour, perhaps because at IGCSE we don't learn how to test for blue food colouring