2.4 Reactivity SeriesEdexcel IGCSE Chemistry: Revision notes
Section 1
How is the reactivity series worked out?
The reactivity series ranks metals in order of how readily they react. It can be built up from two types of evidence:
- Reactions with water and dilute acid — more reactive metals react more vigorously (or at all) with cold water and with dilute hydrochloric or sulfuric acid, producing hydrogen gas and a salt; less reactive metals react slowly or not at all.
- Displacement reactions — a more reactive metal will displace a less reactive metal from a metal oxide (by heating together) or from an aqueous solution of its salt. If metal A displaces metal B from a solution of B's salt, A is more reactive than B.
The full order (most to least reactive) that you need to know is:
potassium, sodium, lithium, calcium, magnesium, aluminium, zinc, iron, copper, silver, gold
A useful mnemonic for the order is: Please Send Lions, Cats, Monkeys And Zebras In Cars, Some Gently — Potassium, Sodium, Lithium, Calcium, Magnesium, Aluminium, Zinc, Iron, Copper, Silver, Gold.
Section 2
How does rusting happen and how can it be prevented?
Rusting is the corrosion of iron. It requires both water and oxygen to be present — iron will not rust in dry air or in oxygen-free water.
iron + water + oxygen → hydrated iron(III) oxide (rust)
Rusting can be prevented by:
- Barrier methods: painting, oiling/greasing, or coating with plastic to keep out air and water.
- Galvanising: coating steel with a layer of zinc, which acts as a barrier and, if scratched, is more reactive than iron so corrodes preferentially (sacrificial protection built in).
- Sacrificial protection: attaching a more reactive metal (e.g. zinc or magnesium) to iron; the more reactive metal corrodes instead of the iron, protecting it even if the surface is damaged.
Rusting needs BOTH water and oxygen — a common error is saying only one is required.
Section 3
What do oxidation, reduction and redox mean?
These terms can be defined in two equivalent ways:
| Term | In terms of oxygen | In terms of electrons |
|---|---|---|
| Oxidation | Gain of oxygen | Loss of electrons |
| Reduction | Loss of oxygen | Gain of electrons |
| Redox | Both oxidation and reduction happening together | Both happening together |
An oxidising agent oxidises another substance (by supplying oxygen or accepting electrons) and is itself reduced. A reducing agent reduces another substance (by removing oxygen or supplying electrons) and is itself oxidised.
OIL RIG: Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).
Section 4
How do reactions with acids show the reactivity series?
Reactive metals react with dilute hydrochloric or sulfuric acid to produce a salt and hydrogen gas:
metal + acid → salt + hydrogen
For example: magnesium + hydrochloric acid → magnesium chloride + hydrogen (Mg + 2HCl → MgCl2 + H2)
The rate of bubbling (fizzing) and how vigorous the reaction is indicates reactivity: more reactive metals like magnesium react quickly and vigorously; less reactive metals like copper do not react with dilute acids at all, because copper is below hydrogen in the reactivity series.
Adding magnesium ribbon to dilute hydrochloric acid produces rapid fizzing and the test tube feels warm (exothermic); adding copper produces no reaction.
Must Know
- Reactivity series (most to least reactive): potassium, sodium, lithium, calcium, magnesium, aluminium, zinc, iron, copper, silver, gold.
- Reactivity can be shown by reactions with water/dilute acid, and by displacement reactions (more reactive metal displaces less reactive metal from its oxide or salt solution).
- Rusting of iron requires both water AND oxygen; prevented by barrier methods, galvanising, or sacrificial protection.
- Oxidation = gain of oxygen / loss of electrons; reduction = loss of oxygen / gain of electrons; redox = both happening together.
- An oxidising agent is itself reduced; a reducing agent is itself oxidised.
- Metal + acid → salt + hydrogen (for metals above copper in the series).
That's the notes covered.
Carry on to the next subtopic.