The Reactivity Series and Displacement Reactions
The reactivity series ranks metals by how readily they lose electrons to form positive ions. It predicts nearly every metal reaction on the syllabus.
1. The order
Potassium, Sodium, Calcium, Magnesium, Aluminium, (Carbon), Zinc, Iron, (Hydrogen), Copper, Silver, Gold
A mnemonic: Please Send Cats, Monkeys And Cute Zebras Into Hot Countries Signed Gold.
Carbon and hydrogen are included even though they are not metals — because they are the reference points for extraction (carbon) and for reactions with acid (hydrogen).
Learn the order. Not being able to recall it was a recorded error, and every prediction on this page depends on it.
More reactive metals LOSE electrons more easily to form positive ions.
2. Reaction with water and steam
| Metals | With cold water | With steam |
|---|---|---|
| K, Na, Ca | vigorous — metal hydroxide + hydrogen | — |
| Mg, Zn, Fe | very slow or none | metal oxide + hydrogen |
| Cu, Ag, Au | no reaction | no reaction |
With cold water: metal + water → metal hydroxide + hydrogen
2Na + 2H₂O → 2NaOH + H₂
With steam: metal + steam → metal oxide + hydrogen
Mg + H₂O → MgO + H₂
The products are DIFFERENT: a hydroxide with cold water, an OXIDE with steam. This distinction is examined regularly.
Magnesium and steam give a WHITE SOLID (magnesium oxide). Not recalling this observation was recorded — magnesium burns with a bright white flame and leaves a white powder.
3. Reaction with dilute acid
metal + acid → salt + HYDROGEN
Only metals ABOVE hydrogen in the series react.
Copper, silver and gold do NOT react with dilute acids, because they are below hydrogen.
Observations: effervescence (bubbles), the metal dissolving, and the mixture warming.
The gas produced is HYDROGEN — confusing it with sulfur dioxide was recorded. (Sulfur dioxide comes from concentrated sulfuric acid, which is beyond the usual dilute-acid reaction.)
Testing it: a lighted splint gives a squeaky pop.
Which salt forms:
- hydrochloric acid → chloride
- sulfuric acid → sulfate
- nitric acid → nitrate
4. Aluminium — the exception
Aluminium appears less reactive than it is, because it forms a thin, unreactive layer of ALUMINIUM OXIDE on its surface, which protects the metal underneath.
This is why aluminium can be used for window frames and drink cans despite being high in the reactivity series. Not knowing about the oxide layer was a recorded error, and it is a standard exam question.
5. Displacement reactions
A MORE reactive metal DISPLACES a LESS reactive metal from its compound.
Example: zinc + copper(II) sulfate → zinc sulfate + copper
Zn + CuSO₄ → ZnSO₄ + Cu
Observations: the blue copper sulfate solution fades, and a red-brown (pinkish) copper solid is deposited.
Copper(II) sulfate solution is BLUE. Zinc sulfate and magnesium sulfate solutions are COLOURLESS. Incorrectly identifying the colour of copper sulfate, and uncertainty about magnesium sulfate’s colour, were both recorded — the colour change is usually the observation the question wants.
A metal cannot displace itself. A recorded error had zinc displacing zinc — the reaction only happens when the metals differ in reactivity.
Using displacement to determine an order: if metal A displaces metal B from solution, A is more reactive than B. A table of “reaction / no reaction” lets you rank them.
6. Ionic equations for displacement
Write the IONIC equation by removing the SPECTATOR IONS — the ones unchanged on both sides.
Full: Zn + CuSO₄ → ZnSO₄ + Cu Ionic: Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)
The sulfate ion is a spectator — it appears unchanged on both sides, so it is left out.
Give the IONIC equation when asked for one. Writing the full equation instead was a recorded error.
Displacement is redox:
Zinc is OXIDISED (loses electrons: Zn → Zn²⁺ + 2e⁻) Copper ions are REDUCED (gain electrons: Cu²⁺ + 2e⁻ → Cu)
7. Using the series
Extraction of metals — the method depends on position:
Above carbon (K, Na, Ca, Mg, Al) → ELECTROLYSIS Below carbon (Zn, Fe, Cu) → reduction with CARBON Very unreactive (Ag, Au) → found native (uncombined)
Thermal stability of carbonates: carbonates of more reactive metals are harder to decompose.
8. Mistakes that cost marks
Not knowing the order of the series.
Saying copper reacts with dilute acid.
Giving a hydroxide as the product with steam (it’s an oxide).
Naming the wrong gas from metal + acid.
Not knowing about aluminium’s oxide layer.
Wrong solution colours in displacement.
Saying a metal displaces itself.
Writing the full equation when the ionic one was asked for.
Including spectator ions in an ionic equation.
Frequently asked questions
What is the reactivity series? A ranking of metals by how readily they lose electrons to form positive ions.
Which metals react with cold water? Potassium, sodium and calcium — giving a hydroxide + hydrogen.
What do metals give with steam? A metal OXIDE + hydrogen.
Which metals react with dilute acid? Those above hydrogen in the series.
What gas is produced with acid? Hydrogen — tested with a squeaky pop.
Why does aluminium seem unreactive? It has a protective layer of aluminium oxide.
What is a displacement reaction? A more reactive metal displaces a less reactive one from its compound.
What colour is copper sulfate solution? Blue — it fades as copper is displaced.
How do I write an ionic equation? Remove the spectator ions that are unchanged on both sides.
Is displacement a redox reaction? Yes — the more reactive metal is oxidised, the metal ion is reduced.
Quick revision checklist
- I know the order of the reactivity series, including C and H
- I know which metals react with cold water and which with steam
- I know the products differ: hydroxide vs oxide
- I know only metals above hydrogen react with acid
- I know the gas is hydrogen and how to test it
- I know which salt each acid forms
- I can explain aluminium’s apparent unreactivity
- I can predict displacement reactions
- I know the solution colours for the common salts
- I can write ionic equations, removing spectators
- I can identify what is oxidised and reduced
- I can use the series to choose an extraction method
These notes cover the reactivity series and displacement reactions in the Cambridge IGCSE Chemistry (0620) syllabus and are written for Grade 9–11 / Year 10–11 students. They are based on teaching patterns observed across a large set of one-to-one IGCSE Chemistry lessons, with particular attention to the errors students make most often and the wording examiners reward. Always check the current syllabus for your own exam series.
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