Where is carbon in the reactivity series?

In this experiment, students heat carbon with various metal oxides, looking for evidence of a reaction. They use their results to determine carbon’s position in the reactivity series. Students can then observe as the teacher burns magnesium in carbon dioxide, producing carbon and magnesium oxide.

Altogether, the class practical and demonstration should take about one hour.

Equipment

Apparatus

• Eye protection

Class practical: heating carbon with metal oxides

• Hard glass test tubes, 3 (see note 9 below)
• Bunsen burner
• Heat resistant mat
• Test tube holder
• Magnet

Demonstration: the reaction of magnesium with carbon dioxide

• Carbon dioxide cylinder (or CO₂ gas generator – see standard techniques for generating, collecting and testing gases)
• Gas jar and lid
• Tongs
• Bunsen burner
• Scissors

Health, safety and technical notes

• Read our standard health and safety guidance.
• Wear eye protection throughout.
• Carbon, C(s) – see CLEAPSS Hazcard HC021.
• Carbon dioxide gas, CO₂(g) – see CLEAPSS Hazcard HC020a. 
• Magnesium oxide, MgO(s) – see CLEAPSS Hazcard HC059b. 
• Magnesium ribbon, Mg(s) – see CLEAPSS Hazcard HC059A. 
• Copper(II) oxide, CuO(s), (HARMFUL, DANGEROUS FOR THE ENVIRONMENT) – see CLEAPSS Hazcard HC026. 
• Iron(III) oxide, Fe₂O₃(s) – see CLEAPSS Hazcard HC055A. 
• It is not possible to completely clean the test tubes from the class practical. Perhaps a box of ‘used test tubes’ can be used for this experiment.

Procedure

Class practical: heating carbon with metal oxides

1. Light a Bunsen burner.
2. Mix together one small spatula measure of carbon powder 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 any glow that persists well after the tube has been taken out of the flame. Also look for any colour change in the tube.
4. Repeat the experiment using a mixture of carbon powder and magnesium oxide.
5. Prepare a mixture of iron oxide and carbon as in step 2 above.
6. Hold the test tube horizontally and run a magnet under the glass. See whether any part of the mixture is magnetic.
7. Heat the iron oxide and carbon mixture strongly in the test tube, and watch for signs of any change.
8. When you have heated for five minutes, allow the tube to cool. Test for the presence of any magnetic particles, as in step 6.
9. For each experiment, record the following:
   • Appearance of the mixture at the start (including, for the iron oxide/carbon mixture, ‘is it magnetic?’)
   • Appearance of the mixture during heating
   • Appearance of the mixture after heating (including, for the iron oxide/carbon mixture, ‘is it magnetic?’)

Demonstration: the reaction of magnesium with carbon dioxide

1. Using a gas cylinder, or a gas generator, fill a gas jar with carbon dioxide and cover with a greased lid.
2. Using scissors, cut a 10 cm piece of magnesium ribbon.
3. Light a Bunsen burner.
4. Hold the magnesium ribbon in tongs, and place one end in a Bunsen burner flame. As soon as it ignites, remove the lid from the gas jar and quickly plunge the ribbon into the carbon dioxide. The magnesium continues to burn in the carbon dioxide, forming some black specks of carbon and white magnesium oxide.

Teaching notes

Class practical: heating carbon with metal oxides

Students should see a glow in the carbon/copper oxide tube with the formation of red-brown copper. In the carbon/magnesium oxide tube, no glow is visible and the mixture looks the same (black and white particles) at the end. (Note that some references recommend testing for carbon dioxide, but heating carbon powder on its own under these conditions produces this gas.)

Carbon is above copper but below magnesium in the reactivity series.

The reaction is:

Carbon + copper oxide → copper + carbon dioxide

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

Lead oxides are also reduced but care needs to be exercised because of the toxicity of lead.

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.

The reaction between carbon and iron oxide is a bit more subtle. There is no change in the contents of the tube but some magnetic particles are often detected. This can be presumed to be iron, so some reduction has occurred.

Carbon + iron oxide → iron + carbon dioxide

Thus carbon is above iron in the reactivity series (but, for the relative lack of reaction) only just above.

This experiment can lead into a study of the blast furnaces. The ability of carbon to reduce metal oxides changes as the temperature rises. Thus, at a temperature of approximately 1800 degrees Celsius in a blast furnace, carbon is more easily able to reduce iron oxide.

Student questions

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