Reactivity of metal oxides

Showing this video is a good alternative if you are unable to carry out similar reactions in the classroom. It can also be used to assess a student’s understanding of the reactivity series and displacement reactions.

The first reaction shown is the reaction between zinc and copper oxide to produce zinc oxide and copper.

You may wish to pause the video just after the reaction is shown and ask the students to write down the word equation to predict the products.

The zinc oxide and excess reactants are removed by using dilute acid. Copper metal can then be seen as a reactant.

The second reaction is an example of the thermite reaction. Iron oxide and aluminium powder are mixed. The energy needed to start this displacement reaction comes from the exothermic reaction between potassium permanganate and glycerol. The video finishes by showing how the thermite reaction is used to weld railway tracks together.

 

This video shows some examples of displacement reactions that are used to extract metals from their oxides.

 

Some questions you could ask your students after they have watched the video are:

Which metal is more reactive: zinc or copper? How does the first reaction prove this?

Zinc is more reactive than copper. This is proved by the first reaction because the zinc displaces the copper from its compound:

zinc + copper oxide à copper + zinc oxide

What is the function of the dilute acid?

To prove that copper is made. The acid reacts with the zinc oxide (plus any remains of the reactants) to remove it. However, the copper does not react with the acid because it is not reactive enough.

Write the word equation for the thermite reaction

aluminium + iron oxide à iron + aluminium oxide

Is the thermite reaction endothermic or exothermic? How can you tell?

It is exothermic – and gives out a lot of energy. You can tell because of the very bright flash of light that is produced during the reaction and the iron produced is molten so has been heated above its melting point.

When iron is added to copper sulfate solution, copper metal forms on the outside of the nail. Use this, plus the information from the video, to place the metals copper, iron and aluminium in order of their reactivity.

Iron displaces copper but aluminium displaces iron in the thermite reaction so the correct order with the most reactive metal first is: aluminium, iron, copper.

 

To introduce your students to the chemistry behind iron extraction using the blast furnace ask them to read Oops! When science goes wrong – the blast furnace