Extracting metals with charcoal

Class practical

In each of the two experiments, illustrating the idea of competition between metals and carbon, students heat a metal oxide with powdered charcoal. If the carbon is more reactive than the metal it will remove the oxygen from the metal oxide and leave traces of the metal in the reaction vessel. The first experiment uses lead(II) oxide; the second modifies the technique slightly and uses copper(II) oxide.
 

Lesson organisation

The solids may be dispensed in plastic weighing dishes. It is best not to issue all three solids at the same time because students may confuse the charcoal and the copper oxide.

The experiment should take about 30 minutes.

Health & Safety and Technical notes

Read our standard health & safety guidance

Wear eye protection throughout. The room should be well ventilated. 

Powdered charcoal, C(s) - see CLEAPSS Hazcard.

Copper(II) oxide, CuO(s), (HARMFUL, DANGEROUS FOR THE ENVIRONMENT) - see CLEAPSS Hazcard.

Lead(II) oxide, PbO(s), (TOXIC, DANGEROUSFOR THE ENVIRONMENT) - see CLEAPSS Hazcard 

1 Test-tubes made of heat resistant borosilicate glass (Pyrex or similar) must be used. Test-tubes with a capacity of about 10 cm³ are ideal. It is important that the test-tubes are dry. Heating lead and its compounds strongly in glass often results in the lead compounds fusing into the glass, rendering the test-tube impossible to re-use. If this is an issue, old but unstained test-tubes can be used and discarded after this use. 

Procedure

Experiment 1
a Transfer one small spatula measure of lead(II) oxide to the empty weighing dish.

b Add one spatula measure of charcoal powder.

c Mix the two powders together using a spatula.

d Transfer the mixture into a hard-glass test tube and strongly heat this mixture for five minutes in a Bunsen flame.

e Allow the test-tube to cool in its holder on a heat resistant mat.

f Tip the cooled mixture out onto the heat resistant mat.

Experiment 2

a Transfer one spatula measure of copper(II) oxide to a hard glass test-tube.

b Carefully add one spatula of charcoal powder on top of the copper oxide without any mixing.

c Strongly heat these two layers for five minutes in a Bunsen flame.

d Allow to cool and then look closely at where the powders meet in the test-tube.

Teaching notes

In each case the students should look for signs that reaction has occurred producing the metal. The copper should be obvious from its colour. The lead may be less obvious; it may appear as globules or as grey powder.

The reactions confirm the place of carbon in the reactivity series, above lead and copper, as it reduces the metal oxides to the metals and is itself oxidised to carbon dioxide:

CuO(s) + C(s) → Cu(s) + CO₂(g) and PbO(s) + C(s) → Pb(s) + CO₂(g).
 

Related experiments

The reaction between zinc and copper oxide

Displacement reactions between metals and their salts

The thermite reaction