Illustrate the idea of competition reactions by reacting copper(II) oxide and zinc metal together, causing an exothermic reaction.

Demonstration

In this experiment copper(II) oxide and zinc metal are reacted together. The reaction is exothermic and the products can be clearly identified. The experiment illustrates the difference in reactivity between zinc and copper and hence the idea of competition reactions.

Lesson organisation

In this experiment copper(II) oxide and zinc metal are reacted together. The reaction is exothermic and the products can be clearly identified. The experiment illustrates the difference in reactivity between zinc and copper and hence the idea of competition reactions.

Apparatus Chemicals

Eye protection

Bunsen burner

Tin lid sitting on a tripod (or a strip of ceramic paper)

Beaker (100 cm3)

Circuit tester (battery, bulb and leads) (Optional)

Safety screens (Optional)

Test-tubes, 2 (Optional – see Procedure g)

Test-tube rack

Access to a balance weighing to the nearest 0.1 g

The quantities given are for one demonstration:

Copper(II) oxide powder (HARMFUL, DANGEROUS FOR THE ENVIRONMENT), 2 g

Zinc powder (HIGHLY FLAMMABLE, DANGEROUS FOR THE ENVIRONMENT), 1.6 g

Dilute hydrochloric acid, approx. 2 M (IRRITANT), 20 cm3

Zinc oxide (DANGEROUS FOR THE ENVIRONMENT), a few grams

Copper powder, a few grams.

Concentrated nitric acid (CORROSIVE, OXIDISING), 5 cm3 (Optional – see Procedure 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 eye protection throughout. Consider placing safety screens around the experiment (Samples of zinc can vary considerably in reactivity, depending on particle size and the state of surface oxidation.)

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

Zinc powder, Zn(s), (HIGHLY FLAMMABLE, DANGEROUS FOR THE ENVIRONMENT)  - see CLEAPSS Hazcard. 

Dilute hydrochloric acid, HCl(aq), (IRRITANT)  - see CLEAPSS Hazcard and CLEAPSS Recipe Book.

Concentrated nitric acid, HNO3(aq), (CORROSIVE, OXIDISING)  - see CLEAPSS Hazcard. 

Copper powder, Cu(s)  - see CLEAPSS Hazcard. 

Zinc oxide, ZnO(s), (DANGEROUS FOR THE ENVIRONMENT) - see CLEAPSS Hazcard.

Procedure

a Weigh out 2 g (0.025 mol) of copper(II) oxide and 1.6 g (0.025 mol) of zinc powder.

b Mix thoroughly to give a uniformly grey powder.

c Pour the mixture in the shape of a ‘sausage’ about 5 cm long onto a clean tin lid sitting on top of a tripod (or onto a strip of ceramic paper, folded lengthwise into a V-shape).

d Heat one end of the ‘sausage’ from above with a roaring Bunsen flame until it begins to glow, then remove the flame. A glow will spread along the ‘sausage’ until it has all reacted. A white/grey mixture will remain.

e Heat this to show that the white powder (zinc oxide) is yellow when hot and white when cool.

f Pour the cool residue into a 100 cm3 beaker and add a little dilute hydrochloric acid to dissolve the zinc oxide (and also any unreacted zinc and copper oxide), warming if necessary. Red-brown copper will be left. This can be rinsed with water and passed around the class for observation. Show that the powder conducts electricity using a circuit tester.

g If further confirmation of identity is required, treat a small amount of the red-brown powder with a few drops of concentrated nitric acid in a test-tube in a fume cupboard. A brown gas, nitrogen dioxide, NO2(g) (VERY TOXIC), is given off as the copper reacts and dissolves. After the reaction adding a little water makes the blue solution of copper(II) nitrate visible.

Teaching notes

The depth of discussion depends on the level of the students involved. Essentially it is a competition between metal(1) and metal(2) for oxygen in a reaction represented by:

Metal(1) + Metal(2) oxide → Metal(1) oxide + Metal(2)

The more reactive metal displaces the less reactive metal from its oxide, as in the case of zinc and copper(II) oxide, for example:

Zn(s) + CuO(s) → ZnO(s) + Cu(s)

Demonstrate that zinc oxide goes yellow when heated and returns to white when cool to help confirm the identity of this product. (This phenomenon is caused by a change in crystal structure - a genuine example of a ‘physical change’.)

Where appropriate, it could be pointed out that these reactions are redox reactions, the more reactive metal behaving as a reducing agent, and the metal oxide acting as an oxidising agent. This could be extended to consider these redox reactions in terms of the loss and gain of electrons by the metals.

Other metals can be used, but take care to compare like with like. Coarse magnesium powder, for example, gives a less vigorous reaction than powdered zinc. Finely powdered magnesium gives a very vigorous reaction and should only be attempted with great care. The reaction between aluminium powder and copper oxide is almost explosive and must not be attempted.

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

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Page last updated November 2016