9.4 Reactivity series
- Syllabus
- 0620–2026–2027
- Topic
- 9.4
- Level
- —
Learning objectives
9.4.1Order of the reactivity series as• State the order of the reactivity series as: potassium, sodium, calcium, magnesium, aluminium, carbon, zinc, iron, hydrogen, copper, silver, gold9.4.2Reactions of metals with• Describe reactions of metals with water/steam/acids: potassium, sodium and calcium with cold water; magnesium with steam; magnesium, zinc, iron, copper, silver and gold with dilute hydrochloric acid; link to reactivity series9.4.3Deduce an order of reactivity from a• Deduce an order of reactivity from a given set of experimental results9.4.4Relative reactivities of metals in• Describe relative reactivities of metals in terms of their tendency to form positive ions, by displacement reactions, if any, with the aqueous ions of magnesium, zinc, iron, copper and silver9.4.5Apparent unreactivity of aluminium in• Explain the apparent unreactivity of aluminium in terms of its oxide layer
Recall the reactivity series
Most reactive → K > Na > Ca > Mg > Al > C > Zn > Fe > H > Cu > Ag > Au → least reactive.
| Position | Meaning |
|---|---|
| above carbon | metal is too reactive for carbon reduction of its oxide |
| below carbon | oxide may be reduced by carbon |
| above hydrogen | metal can release hydrogen from dilute acid |
| below hydrogen | metal does not normally release hydrogen from dilute acid |
Write every member before using a position. Carbon and hydrogen are comparison benchmarks even though they are non-metals; they must remain in the stated order.
Do not omit carbon or hydrogen, and do not swap zinc and iron or copper and silver. The direction is from potassium, the most reactive, to gold, the least reactive.
Predict metal reactions from series position
| Metal and reagent | Expected result | Products |
|---|---|---|
| potassium + cold water | very vigorous | potassium hydroxide + hydrogen |
| sodium + cold water | vigorous | sodium hydroxide + hydrogen |
| calcium + cold water | reacts readily | calcium hydroxide + hydrogen |
| magnesium + steam | reacts on heating | magnesium oxide + hydrogen |
| magnesium + dilute HCl | vigorous | magnesium chloride + hydrogen |
| zinc + dilute HCl | moderate | zinc chloride + hydrogen |
| iron + dilute HCl | slower | iron(II) chloride + hydrogen |
| copper, silver or gold + dilute HCl | no reaction | none |
Examples: 2Na + 2H₂O → 2NaOH + H₂; Mg + H₂O(g) → MgO + H₂; Zn + 2HCl → ZnCl₂ + H₂.
Higher position means greater tendency to react. Metals above hydrogen displace H⁺ from dilute hydrochloric acid; metals below hydrogen do not. With water, the more reactive named metals react under milder conditions.
Keep conditions and products paired: cold water gives a hydroxide, steam gives an oxide. Magnesium is specified with steam; copper, silver and gold do not react with dilute hydrochloric acid.
Deduce a reactivity order from results
| Experimental result | Deduction |
|---|---|
| A displaces B from B ions | A > B |
| A does not displace B | A < B, if conditions are suitable |
| A reacts more vigorously with the same acid/water condition | A is more reactive |
| A reacts with cold water, B only with steam | A > B |
| A releases H₂ from dilute acid, B does not | A > H > B |
| carbon reduces A oxide but not B oxide | B > C > A |
Translate every observation into an inequality, combine overlapping inequalities into one chain, then check every result against the final order. For A > B and C > A, the combined order is C > A > B.
A no-reaction result gives a directional constraint only when the reagents and conditions would allow a displacement. Use multiple results to resolve unknowns and do not infer an exact gap in reactivity.
The deposited metal is the less reactive metal displaced from its ions. Do not reverse the inequality: if zinc deposits copper from Cu²⁺ solution, zinc is more reactive than copper.
Explain aqueous metal displacement
A more reactive metal has a greater tendency to lose electrons and form positive ions. It displaces a less reactive metal from an aqueous solution of that metal's ions.
| Required relative order | What a solid metal can displace below it |
|---|---|
| Mg > Zn > Fe > Cu > Ag | magnesium can displace Zn²⁺, Fe²⁺/Fe³⁺, Cu²⁺ and Ag⁺; zinc can displace iron, copper and silver ions; iron can displace copper and silver ions; copper can displace silver ions; silver displaces none above it |
Example: Mg(s) + Cu²⁺(aq) → Mg²⁺(aq) + Cu(s). Magnesium atoms lose electrons and form Mg²⁺; copper ions gain electrons and form copper metal.
Compare the solid metal with the metal named by the aqueous ion. If the solid is higher in the series, reaction occurs; if it is lower, write no reaction.
Do not compare the spectator ion such as sulfate or nitrate. The direction is controlled by the two metals: the more reactive atom forms positive ions while the less reactive ion becomes metal.
Explain aluminium's apparent unreactivity
Aluminium is reactive, but its surface rapidly forms a thin, adherent layer of aluminium oxide.
| Stage | Effect |
|---|---|
| aluminium surface contacts oxygen | Al₂O₃ layer forms |
| oxide layer covers the metal | air, water or reagent cannot easily reach fresh aluminium |
| contact is blocked | reaction appears absent or starts slowly |
| layer is removed or penetrated | the underlying aluminium can react |
The oxide layer explains delayed reaction with dilute hydrochloric acid or copper(II) sulfate and aluminium's resistance to further corrosion in air.
Apparent unreactivity does not mean aluminium is low in the reactivity series. It is above carbon; the protective, unreactive oxide coating creates the misleading observation.