Metal Displacement Reactions (Oxford AQA IGCSE Combined Science Double Award)

Metal Displacement Reactions

What is a displacement reaction?

• A displacement reaction occurs when a more reactive metal will displace a less reactive metal from its compound 

• This can occur by:

  • Reacting a metal with a metal oxide (by heating)

  • Reacting a metal with an aqueous solution of a metal compound

• It is possible to displace copper from copper(II) oxide by heating it with zinc

  • In this reaction, copper oxide is reduced as it has lost oxygen zinc is oxidises as it has gained electrons

zinc + copper(II) oxide → zinc oxide + copper

Zn    +     CuO    →    ZnO    +    Cu

• Zinc has been oxidised as it gained oxygen to form zinc oxide

• Copper(II) oxide has been reduced as it has lost oxygen to form copper

• It is also possible to displace copper from copper(II) sulfate using iron

iron + copper sulfate → iron(II) sulfate + copper 

Fe + CuSO₄ → FeSO₄ + Cu

• We can write this as an ionic equation

• An ionic equation shows only the atoms and ions that have changed in the reaction

Fe + Cu²⁺ + SO₄^2– → Fe²⁺ + SO₄^2– + Cu

• We can then remove the spectator ions to see the overall change

Fe + Cu²⁺→ Fe²⁺ + Cu

Redox in terms of electrons

• This shows that iron has a greater tendency to form ions than copper

• Oxidation and reduction can also be explained in terms of electrons

  • Oxidation is the loss of electrons 

  • Reduction is the gain of electrons

• Fe has lost electrons to form the Fe²⁺ ion so has been oxidised

• Cu²⁺ has gained electrons to form Cu so has been reduced

The redox reaction between Fe and Cu²⁺