The real reactivity of aluminium

Class practical or Demonstration

This experiment illustrates the displacement of copper from copper(II) sulfate solution using aluminium foil. Students add aluminium cooking foil to copper(II) sulfate solution and observe no reaction. Then sodium chloride is added and dissolved. A vigorous displacement reaction occurs and the solution gets very hot, aluminium dissolves and red copper is visible.

Lesson organisation

This class practical can take about 30 minutes to complete A flexicam would work well if this is to be done as a demonstration and allow students a clearer view of what is going on.

Apparatus	Chemicals
Per experiment: Wear eye protection Conical flask (100 cm3)	Per experiment: Aluminium foil, 2 cm x 2 cm Copper(II) sulfate solution 0.8 M (HARMFUL), 20 cm3 Sodium chloride, 2-3 g Refer to Health & Safety and Technical notes section below for additional information.

Health & Safety and Technical notes

Read our standard health & safety guidance

Wear goggles and disposable nitrile gloves.

Aluminium foil, Al(s) - see CLEAPSS Hazcard.

Copper(II) sulfate solution, CuSO₄(aq), 0.8 M (HARMFUL, DANGEROUS FOR THE ENVIRONMENT) - see CLEAPSS Hazcard and CLEAPSS Recipe Book.

Sodium chloride, NaCl(s), (table salt) 

1 Ensure the aluminium foil is completely consumed by the reaction before disposal to prevent a continued exothermic reaction in the rubbish bin. Use plenty of copper(II) sulfate solution and sodium chloride to ensure a complete reaction.

Procedure

a Measure approximately 20 cm³of copper(II) sulfate solution into the conical flask.

b Add a square of aluminium foil.

c Look for signs of a reaction.

d Add a spatula of sodium chloride and stir to dissolve.

e Observe any changes. If nothing happens, add more sodium chloride. Has displacement of copper from copper(II) sulfate occurred?

Student questions and example table.

1. Before the sodium chloride is added, does any reaction occur?

2. After adding sodium chloride, does the aluminium appear more or less reactive?

3. How does the salt affect this change?

Write yes or no.

Observations	Before the sodium chloride is added	After the sodium chloride is added
Bubbles observed
Colour changes
Temperature change
Copper observed

Teaching notes

Aluminium does not show its true reactivity until the oxide layer is disturbed. Sodum chloride disturbs this oxide layer. Scratches on the surface of the oxide layer allow chloride ions to react with aluminium, this effects the cohesiveness of the oxide layer. This allows reaction with the copper(II) sulfate. Remind students what copper looks like, so that they know what they are looking for.

Answers:

1. Aluminium appears less reactive than copper. The aluminium foil appears unable to displace copper from copper(II) sulfate solution.

2. Now aluminium is more reactive because it displaces copper. Aluminium + copper(II) sulfate → copper + aluminium sulfate

3. Scratches on the surface of the oxide layer allow chloride ions to react with aluminium, this effects the cohesiveness of the oxide layer. This allows a simple exchange reaction with the copper(II) sulfate. The protective oxide layer forms  instantly the aluminium is exposed to the air.

Health & Safety checked, 2016

Credits

This Practical Chemistry resource was developed by the Nuffield Foundation and the Royal Society of Chemistry.

© Nuffield Foundation and the Royal Society of Chemistry

Page last updated October 2015