Reacting magnesium with copper(II) oxide

This demonstration activity should take about 20 minutes. The reaction is violent but safe, provided the procedure is followed exactly. A rehearsal is essential if this experiment has not been done before.

Equipment

Apparatus

• Eye protection (note 2)
• Safety screens (note 2)
• Crucible (note 3)
• Pipeclay triangle
• Tripod
• Bunsen burner
• Large sheet of hardboard to protect the bench (or heat resistant mats)
• Scrap paper, 2 pieces

Chemicals

• Magnesium powder (HIGHLY FLAMMABLE), 0.25 g (note 4)
• Copper(II) oxide powder (HARMFUL, DANGEROUS FOR THE ENVIRONMENT), 0.25 g (note 4)

Health, safety and technical notes

• Read our standard health and safety guidance.
• Wear eye protection and use safety screens. The teacher should wear goggles or a face shield, and all students should wear eye protection throughout the demonstration.
• Use a metal crucible rather than a ceramic one. Alternatively, use a steel ‘crown’ bottle top which has had the plastic insert burnt out (in a fume cupboard) – the bottle top must NOT be hot when the magnesium powder/copper oxide mix is added.
• These amounts must not be exceeded unless you are covered by an Explosives Certificate issued by the police, in line with UK Explosives Regulations 2014.
• Magnesium powder, Mg(s), (HIGHLY FLAMMABLE) – see CLEAPSS Hazcard HC059A.
• Copper(II) oxide, CuO(s), (HARMFUL, DANGEROUS FOR THE ENVIRONMENT) – see CLEAPSS Hazcard HC026.

Procedure

1. Protect the bench with a large sheet of hardboard or heat resistant mats.
2. Set up a tripod with a pipeclay triangle and a crucible. Place safety screens around the apparatus.
3. Place the Bunsen burner under the crucible.
4. Move the class to the back of the room, with the safety screen between them and the experiment. They should wear safety glasses. Warn them not to stare at the crucible.
5. Gently mix the small portions of magnesium and copper(II) oxide by putting them on a piece of scrap paper and repeatedly pouring back and forth onto another piece of scrap paper. Add the mixture to the crucible.
6. Light the Bunsen burner (away from the crucible) with the air hole open and then place the Bunsen flame under the crucible. Move quickly to a metre or two in front of the safety screen.
7. After one or two minutes (be patient) a vigorous reaction occurs. Do not stare at the crucible as the flash is bright.
8. If nothing happens, do NOT return to the apparatus but leave it for up to 15 mins. Then turn off the gas at the stopcock, allow the apparatus to cool and then place the crucible and contents in a large beaker of water.
9. Do NOT be tempted to use other metal oxides.

Teaching notes

The reaction is:

Copper oxide + magnesium → copper + magnesium oxide

This shows that magnesium is higher in the reactivity series than copper.

Most of the products are vaporised in the above reaction.