Rotation 2

Module 3 – Environmental chemistry

LessonTitle

1Acids, alkalis and pH

2Neutralisation

3Soil pH

4The causes and effects of acid rain

5The effects of global warming

6Monitoring pollution

Module 4 – Simple chemical reactions

LessonTitle

1History and theory of burning

2Combustion of magnesium

3Fuels and their energy release

4Displacement reactions and their energy release

5Solubility I

6Solubility II

73 + 4 Module test

Year 9H: Module 4 – Simple chemical reactions
Lesson 2 – The combustion of magnesium

Learning objectives

Pupils should learn:

 that magnesium burns to form magnesium oxide

 that the mass (Grams or Kg) increases as an oxygen atom is added to the magnesium atom to form magnesium oxide

 that when a compound is formed it has a fixed composition

 that law of conservation of mass (dealing with chemical change and mass)

 be able to conduct the burning of magnesium experiment

National curriculum reference: Key Stage 3 Sc3 Materials and their properties – 2a & 2g

Sc 1 Scientific enquiry - 2f, 2k & 2l

Key Stage 2 link/Prior learning

Sc3 Materials and their properties – 2f & 2g

Pupils will

 know the theories of burning

 know that magnesium burning in oxygen produces magnesium oxide from the previous lesson

Suggested teaching activities

Teacher demonstration or class practical dealing with chemical change and mass:

Demonstrate to pupils to how they will investigate the effects on mass when burning magnesium ribbon (use spotlight science textbook P34/35)

Pupils are to pool results after experiment conducted. Pupils to make a prediction on the mass to be made before carrying out experiment.

Practical:

Different lengths of magnesium are to be given to pupils. Pupils are to weigh empty crucibles and lid and reweigh with magnesium loosely coiled in the crucible. Crucible is then heated gently at first then more strongly, with lid being lifted on and off regularly to stop fumes escaping but allow oxygen in.

Pupils need to subtract the difference in weight before and after the experiment. This is to find out the difference in mass to prove that the mass increase is due to the oxygen being combined to the magnesium atom to form magnesium oxide (note: mass of oxygen could not be measured initially because it is a gas).

Discuss with pupils the law of conservation of mass.

Mass cannot be lost or gained during a chemical reaction is known as the Law of conservation of mass.

Mention that the magnesium oxide has a fixed composition because magnesium oxide contains one of atom of oxygen for each atom of magnesium.

Ask pupils to give examples where mass would be conserved in everyday situations (e.g. rusting of iron nail, candle wax burning etc.) – chemical change and mass

Results are often too unreliable to plot on graph therefore better to use results given in spotlight science 27d: It’s a Fix. To plot graph of mass of magnesium oxide against mass of magnesium to give a straight line to show mass added is proportional to mass of magnesium used.

Extension

Also carry out 27d: making magnesium chloride from magnesium involves plotting a similar graph.

Q3 P35 spotlight science.

Resources/References

15 crucibles and lids, 15 strips of magnesium of varying lengths, top-balance, tongs, heating apparatus, pipe clay triangle, calculators

Worksheets – burning of magnesium

Core chemistry C2.10: chemical change and mass P135

Spotlight science Year 9: 27d: It’s a fix with corresponding worksheets

Homework

Write up the experiment including a results table, pooled graph and conclusion.

Complete worksheet on the burning magnesium.

Safety/Risk Assessment

Safety glasses must be worn and care should be taken handling hot crucible and lid, using tongs.

Ensure that pupils don’t look directly at the magnesium ribbon burning – a strong white glow.

Additional Notes

This experiment can be unreliable, especially if too many fumes are allowed to escape – the lid has to be carefully lifted using the tongs to allow oxygen into the heated crucible with magnesium.