The reactivity of iron

In this experiment, students heat iron metal with the oxides of two other metals, copper and magnesium, to determine its position in the reactivity series. At each stage, students look for signs of a reaction.

The practical should take about 20–30 minutes.

Equipment

Apparatus

• Eye protection
• Test tubes (see note 6 below)
• Bunsen burner
• Heat resistant mat
• Test tube holder
• Spatula

Chemicals

• Iron filings, 2 spatula measures
• Magnesium oxide, 1 spatula measure
• Copper(II) oxide (HARMFUL, DANGEROUS FOR THE ENVIRONMENT), 1 spatula measure

Health, safety and technical notes

1. Read our standard health and safety guidance.
2. Wear eye protection throughout.
3. Iron filings, Fe(s) – see CLEAPSS Hazcard HC055A.
4. Magnesium oxide, MgO(s) – see CLEAPSS Hazcard HC059b.
5. Copper(II) oxide, CuO(s), (HARMFUL, DANGEROUS FOR THE ENVIRONMENT) – see CLEAPSS Hazcard HC026.
6. It may not be possible fully to clean the test tubes from this experiment. You may wish to consider keeping a box of ‘used test tubes’ for this reason.

Procedure

1. Light a Bunsen burner
2. Mix together one small spatula measure of iron filings and an equal measure of copper(II) oxide in a test tube. Move the tube from side to side to mix the solids.
3. Hold the tube in a test tube holder. Heat the tube strongly with a roaring Bunsen flame. Look for signs of a reaction. Look for a glow that persists well after the tube has been taken out of the flame, and look for any colour change in the tube.
4. Repeat the experiment using a mixture of iron filings and magnesium oxide.
5. Record, for each experiment:
   • The appearance of the mixture at the start
   • The appearance of the mixture during heating
   • The appearance of the mixture after heating

Teaching notes

Students should see a glow in the iron/copper oxide tube and red-brown copper forms. In the iron/magnesium oxide tube, there is no glow and the mixture should look the same (grey and white particles) at the end.

Thus, iron is above copper but below magnesium in the reactivity series.

The reaction that occurs is:

Iron + copper oxide → copper + iron oxide

Copper oxide is reduced to copper by the iron (reduction is removal of oxygen, at this level).

Lead oxides are also reduced but should not be used as they give toxic vapours.

Zinc oxide can be used as another unreactive oxide but the fact that it turns yellow on heating (but then back to white on cooling) may confuse students.

Student questions

1. In which tube does a reaction occur?
2. What signs of reaction are there?
3. What can you conclude about the positions of magnesium, iron and copper in the reactivity series?
4. Write word equations for any reactions that occur.
5. In these reactions, what is being reduced?