Where does carbon come in the reactivity series?

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Lesson organisation

This can be done as a class practical (Experiment 1) and a demonstration (Experiment 2). Altogether, they should take about one hour.

Apparatus and chemicals

Eye protection

Experiment 1 Heating carbon with metal oxides

Each working group requires:

Hard glass test-tubes, 3 (see note 1)
Bunsen burner
Heat resistant mat
Test-tube holder
Magnet

Carbon (dry powdered wood charcoal) (Low hazard)
Magnesium oxide (Low hazard)
Copper(II) oxide (Harmful, Dangerous for the environment)
Iron(III) oxide (Low hazard)

Experiment 2 The reaction of magnesium with carbon dioxide

For one demonstration:

Magnesium ribbon (Low hazard), 10 cm
Carbon dioxide cylinder (or CO₂ gas generator) (Low hazard). See Standard techniques: Generating, collecting and testing gases
Gas jar and lid
Tongs
Bunsen burner
Scissors

Technical notes

Carbon (Low hazard) Refer to CLEAPSS Hazcard 21
Carbon dioxide (Low hazard) Refer to CLEAPSS Hazcard 20
Magnesium oxide (Low hazard) Refer to CLEAPSS Hazcard 59B
Magnesium ribbon (Low hazard) Refer to CLEAPSS Hazcard 59A
Copper(II) oxide (Harmful, Dangerous to the environment) Refer to CLEAPSS Hazcard 26
Iron(III) oxide (Low hazard) Refer to CLEAPSS Hazcard 55A

1 It is not possible to completely clean the test-tubes from Experiment 1. Perhaps a box of ‘used test-tubes’ can be used for this experiment.

Procedure

HEALTH & SAFETY: Wear eye protection

Experiment 1 Heating carbon with metal oxides

a Light a Bunsen burner.

b 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.

c 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.

d Repeat the experiment using a mixture of carbon powder and magnesium oxide.

e Prepare a mixture of iron oxide and carbon as in b above.

f Hold the test-tube horizontally and run a magnet under the glass. See whether any part of the mixture is magnetic.

g Heat the iron oxide and carbon mixture strongly in the test-tube, and watch for signs of any change.

h When you have heated for 5 minutes, allow the tube to cool. Test for the presence of any magnetic particles, as in part f.

i 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?’).

Experiment 2 The reaction of magnesium with carbon dioxide

Demonstration

a Using a gas cylinder, or a gas generator, fill a gas jar with carbon dioxide and cover with a greased lid.

b Using scissors, cut a 10 cm piece of magnesium ribbon.

c Light a Bunsen burner.

d 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 on Experiment 1 '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

Here are some questions to ask your students about Experiment 1 'Heating carbon with metal oxides'.

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?

Health and Safety checked, February 2008

Web links

http://genchem.chem.wisc.edu/demonstrations/Gen_Chem_Pages/06thermopage/thermite_reaction.htm has a video of a thermite reaction in a laboratory.

www.northeast.railfan.net/high_iron.html#thermite has detail of thermite welding of rail tracks.

(Websites accessed August 2007)