The reactivity series, reactions of metals with water and dilute acid, and displacement reactions of metals from solutions of their salts.

What this topic is asking

WJEC wants you to place metals in order of reactivity from how they react with water and acid, and to use that order to predict displacement reactions. This is part of topic 2.3 Metals and their extraction in Unit 2 of WJEC GCSE Chemistry (3430).

Ordering metals by reactivity

Hydrogen and carbon are often included in the series as reference points, because whether a metal reacts with acid (releasing hydrogen) and whether it can be extracted with carbon both depend on its position.

Reactions with water and acid

Displacement reactions

If you add a metal to a salt solution of a less reactive metal, a reaction happens; if the metal is less reactive than the one in solution, nothing happens. This is a quick way to confirm the order experimentally.

In a displacement reaction electrons are transferred: the more reactive metal loses electrons (it is oxidised) and the ions of the less reactive metal gain them (they are reduced). For example, when zinc displaces copper, the zinc atoms become $\text{Zn}^{2+}$ ions while the $\text{Cu}^{2+}$ ions become copper atoms. The energy released often warms the solution, so a temperature rise can also be used to compare reactivity: the bigger the difference in reactivity, the larger the rise. Thermite, in which aluminium displaces iron from iron oxide, is a dramatic example of how much energy a displacement reaction can release.

Try this

Q1. Zinc is added to copper sulfate solution. State whether a reaction occurs and why. [2 marks]

• Cue. Yes; zinc is more reactive than copper, so it displaces copper from the solution.

Q2. State what you would see when calcium is added to cold water. [1 mark]

• Cue. Fizzing as hydrogen is released, with the calcium reacting and a white suspension of calcium hydroxide forming.