Metal Displacement Reactions (WJEC GCSE Chemistry)

Introduction

• The reactivity of metals decreases going down the reactivity series.
• This means that a more reactive metal will displace a less reactive metal from its compounds
• Two examples are:
  • Reacting a metal with a metal oxide (by heating)
  • Reacting a metal with an aqueous solution of a metal compound
• The order of reactivity can be determined using displacement reactions 

Apparatus

• 1 cm strips of zinc, magnesium, copper and iron metal
• 5 cm³ of 0.1 mol dm^–1 zinc sulfate, magnesium sulfate, copper(II) sulfate and iron(II) sulfate
• 4 dropping pipettes
• Dimple tile

Diagram

Diagram to show the set up for the metal displacement reactions

Set up the dimple tray as shown to investigate the reactivity of zinc, magnesium, copper and iron

Method

1. Use the dropping pipette to add one to two drops of zinc sulfate to the first row of dimples 
2. Add one piece of each of the four metals to different dimples (as shown in the diagram)
3. Record any changes in the table
4. Note there will be no change for dimples that involve the metal and compound that are contain the same metal (e.g. zinc and zinc sulfate)
5. Use a different dropping pipette for each solution to avoid contamination
6. If a reaction occurs, add a tick in the correct box, if a reaction does not occur add in a x

	Zinc	Magnesium	Copper	Iron
Zinc sulfate
Magnesium sulfate
Copper(II) sulfate
Iron(II) sulfate

Practical tip

• Careful not to overfill the dimples with solution as these will overflow and contaminate the other reactions

Analysis of Results 

Results

Results table

	Zinc	Magnesium	Copper	Iron
Zinc sulfate	-	✓	x	x
Magnesium sulfate	x	-	x	x
Copper(II) sulfate	✓	✓	-	✓
Iron(II) sulfate	✓	✓	x	-

Conclusion

• Magnesium displaces the other metals out of solution
• Zinc displaces iron and copper out of solution, iron will only displace copper out of solution
• Copper does not displace any metal out of solution
• The equations for the reactions that occur are

Mg + ZnSO₄ → Zn + MgSO₄

Mg + CuSO₄ → Cu + MgSO₄

Mg + FeSO₄ → Cu + FeSO₄

Evaluation

• The metal that shows the most reactions will be the most reactive metal
• This is because it has displaced the other metals out of the sulfate solution
• Therefore we can deduce that the order of reactivity is
  • Magnesium (most reactive)
  • Zinc
  • Iron
  • Copper (least reactive)