Lesson focus: A more reactive metal can displace a less reactive metal from a compound because it forms positive ions more readily.
Predict and explain metal displacementA reaction where a more reactive element pushes a less reactive element out of its compound. reactions using reactivity, electron transfer and controlled evidence.
Build on earlier learning
Metals and waterWater reactions established a relative order for several metals. Displacement tests that order against metal ions in compounds.
Practical
Displacement reactions
- Add a piece of each metal to solutions of the other metals’ salts in a spotting tile.
- Look for a coating on the metal or a colour change in the solution.
- A more reactive metal displaces a less reactive one.
Record: A grid of ✓ (reaction) and ✗ (no reaction) used to build a reactivity series.
You will be successful when you can…
- Apply the displacement rule.
- Write word equations.
- Explain electron transfer qualitatively.
- Interpret colour and coating evidence cautiously.
Words that carry the science
- displacement
- A reaction in which a more reactive element replaces a less reactive element in a compound.
- aqueous
- Dissolved in water.
- metal ion
- A positively charged particle formed when a metal atom loses electrons.
- redox
- A reaction in which oxidation and reduction occur together through electron transfer.
- deposit
- A solid product formed on a surface or from a solution.
- spectator ion
- An ion present but unchanged in the overall ionic reaction.
Use displacement as a test of relative reactivity
01Relative reactivity determines the direction
A more reactive metal displaces a less reactive metal from its compound. zinc + copper sulfate → zinc sulfate + copper occurs because zinc is above copper in the reactivity series.
Copper placed in zinc sulfate does not react because copper does not form ions more readily than zinc. A no-reaction result is useful only if surfaces, concentration, time and temperature were suitable.
02Atoms and ions exchange electrons
Zinc atoms lose electrons and become Zn²⁺; Cu²⁺ ions gain electrons and become copper atoms. Zinc is oxidised and copper ions are reduced, so this is a redoxA reaction where one substance loses oxygen (reduction) while another gains it (oxidation). reaction.
Sulfate ions remain in solution as spectator ionAn ion that is in the mixture but does not change during the reaction.. At KS3, word equations and particle reasoning are sufficient; balanced ionic half-equations are an IGCSE bridge.
03Several observations must agree
Copper can appear as a brown depositA layer of solid that forms on a surface during a reaction, such as copper forming on zinc., a blue copper sulfate solution can fade, and the zinc surface can change. Temperature may also rise. Each is evidence, but contamination or oxide layers can complicate it.
Use equal volumes and concentrations, similarly cleaned metal strips and equal times. Copper sulfate is harmful and environmental release should be minimised; use small quantities and dispose of solutions correctly.
Metal displacement reactions
A more reactive metal pushes a less reactive metal out of its compound. The less reactive metal coats the strip and the more reactive metal goes into solution.
Cu ions Mg ions
Cu atoms on the strip
Controls
Reactivity: magnesium > zinc > iron > copper. Temperature rises are illustrative. Copper sulfate solution is blue, so it fades as copper ions are used up.
Predict iron in copper sulfate
An iron nail is placed in copper sulfate solution.
- Iron is above copper in the reactivity series.
- Iron can therefore displace copper ions.
- The products are iron sulfate and copper.
- Write: iron + copper sulfate → iron sulfate + copper.
How to make the reasoning visible: A copper-coloured deposit and loss of blue colour support the prediction, although the exact iron ion formed depends on conditions.
Complete a displacement matrix
A tick means a reaction is predicted from the reactivity order Mg > Zn > Fe > Cu.
| Solid metal | Mg²⁺ solution | Zn²⁺ solution | Fe²⁺ solution | Cu²⁺ solution |
|---|---|---|---|---|
| Magnesium | — | Reaction | Reaction | Reaction |
| Zinc | No reaction | — | Reaction | Reaction |
| Iron | No reaction | No reaction | — | Reaction |
| Copper | No reaction | No reaction | No reaction | — |
Why does zinc react with copper ions but not magnesium ions?
How does the matrix reveal the most reactive solid metal?
Check your understanding
Answer from memory, then check against the suggested answer.
State the metal displacement rule.
Which species gains electrons in zinc plus copper ions?
What is a spectator ion?
Predict whether copper reacts with iron sulfate solution.
Explain why a temperature rise supports but does not by itself prove displacement.
Exam Question Practice
Exam Question Practice
Mark points shown after marking
Zinc powder is added to blue copper sulfate solution.
Explain why a reaction happens.
(2)Explain what happens to the particles and what is observed.
(3)Total for this question: 5 marks
Command word: For explainA command word: say how or why something happens, giving reasons with words like "because" or "so"., connect reactivity → electron transfer → products → visible evidence.