Metal Displacement Reactions — The Reactivity Series | IGCSE Chemistry

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 6% of your exam marks.

stable

Low

Stable6%

Displacement reactions and determining order of reactivity from experimental data.

The displacement principle

A more reactive metal will displace a less reactive metal from its compound
This applies to two situations:
- Heating a metal with a solid metal oxide
- Adding a metal to an aqueous solution of a metal salt
The reactive metal takes the oxygen, or the negative ion, leaving the less reactive metal as the free element

Displacement from metal oxides

Heat zinc powder with copper(II) oxide:

Zn(s) + CuO(s) → ZnO(s) + Cu(s)

- Zinc takes the oxygen, leaving copper as the brown solid product
- Zinc is the **reducing agent** (it removes oxygen); copper(II) oxide is the **oxidising agent**

The thermite reaction uses aluminium to extract iron from iron(III) oxide:

2 Al(s) + Fe₂O₃(s) → 2 Fe(l) + Al₂O₃(s)

- The reaction releases enough heat to melt the iron, which is why thermite was used to weld railway tracks

No reaction occurs if the added metal is less reactive than the metal in the oxide (e.g. silver added to lead(II) oxide does nothing)

Displacement from salt solutions

Add a strip of magnesium to blue copper(II) sulfate solution:

Mg(s) + CuSO₄(aq) → MgSO₄(aq) + Cu(s)

- The blue colour fades as colourless magnesium sulfate forms
- Pink-brown copper plates onto the magnesium and any loose metal sinks to the base of the beaker

Add iron filings to copper(II) sulfate solution:

Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

- Pale-green iron(II) sulfate forms, copper coats the iron

A metal placed in a salt solution of a more reactive metal gives no reaction (e.g. copper in zinc sulfate does nothing)

Exam tip

Describing observations in a displacement experiment

What comes up: the exam gives you a displacement reaction in solution (for example, adding iron to copper sulfate) and asks you to name the type of reaction and describe what you see.

Write (two marks): (1) name it a displacement reaction (the mark scheme also accepts redox / oxidation and reduction). (2) describe the solid product by colour: for copper depositing, the credited colour is pink-brown or pink; the mark scheme also accepts orange-brown and red-brown but rejects "red" alone, and ignores simply writing "copper".

Watch out: a metal cannot displace itself — a metal in a solution of its own salt gives no reaction because it is not more reactive than its own ions.