Reactivity Series and Corrosion
ChemistryΒ· 9.4, 9.5 (2026-2028 Syllabus)Β· 25 min read
1. Core: Reactivity Series Order & Reaction Rulesβ β ββββ± 8 min
Reactivity Series
A ranked list of metals (plus non-metals carbon and hydrogen) ordered from most reactive to least reactive, used to predict chemical reaction outcomes.
Potassium (K)
Sodium (Na)
Calcium (Ca)
Magnesium (Mg)
Aluminium (Al)
Carbon (C)
Zinc (Zn)
Iron (Fe)
Lead (Pb)
Hydrogen (H)
Copper (Cu)
Silver (Ag)
Gold (Au)
Use the reactivity series to state if magnesium will react with dilute hydrochloric acid, and write the word equation if the reaction occurs.
- 1
Locate magnesium and hydrogen in the series: magnesium is positioned above hydrogen.
- 2
Apply the rule: metals above hydrogen react with dilute acids to produce a salt and hydrogen gas.
- 3
Reaction occurs, word equation: magnesium + hydrochloric acid β magnesium chloride + hydrogen
Exam tip:
You must memorize the full series including carbon and hydrogen, as they are required for extraction and acid reaction questions.
2. Core: Displacement Reactionsβ β β βββ± 7 min
Displacement Reaction
A reaction where a more reactive metal displaces (replaces) a less reactive metal from a solution of its salt, or from its solid oxide.
A displacement reaction only occurs if the uncombined metal is higher in the reactivity series than the metal in the compound. For example, iron will displace copper from copper sulfate solution, but copper will not displace iron from iron sulfate solution.
A student adds zinc powder to pale green iron(II) sulfate solution. State the observations you would expect, and explain why the reaction occurs using the reactivity series.
- 1
Locate zinc and iron in the series: zinc is above iron, so displacement will occur.
- 2
Observations: grey zinc powder dissolves, pale green solution turns colourless, dark grey iron solid deposits at the bottom of the test tube.
- 3
Explanation: Zinc is more reactive than iron, so it displaces iron from its sulfate salt. Word equation: zinc + iron(II) sulfate β zinc sulfate + iron
3. Core: Rusting & Prevention Methodsβ β ββββ± 7 min
Rusting
The specific corrosion of iron, where iron reacts with oxygen and liquid water to form soft, flaky hydrated iron(III) oxide (rust) that falls off to expose more iron to further corrosion.
Rusting requires both oxygen (from air) and liquid water to occur. If either substance is absent (e.g. iron stored in dry air, or boiled deoxygenated water), rusting cannot happen.
Barrier methods: Coat iron with paint, oil, grease, or plastic to block contact with oxygen and water
Galvanising: Coat iron with a layer of zinc, which acts as a barrier and provides additional protection if scratched
Alloying: Mix iron with chromium and nickel to form stainless steel, which does not rust
An iron garden gate is showing early signs of rust. State two effective methods to prevent further rusting, and explain how each works.
- 1
Method 1: Paint the entire gate surface. This creates an airtight, waterproof barrier that stops oxygen and water from touching the iron, preventing rust formation.
- 2
Method 2: Galvanise the gate. The zinc coating acts as a physical barrier, and will also provide sacrificial protection if the coating is scratched (see Extended section for full explanation).
4. Extended Only: Sacrificial Protectionβ β β β βExtended onlyβ± 7 min
Sacrificial Protection
A corrosion prevention method where a more reactive metal (e.g. zinc or magnesium) is attached to an iron object. The more reactive metal oxidises (corrodes) preferentially, sacrificing itself to protect the iron from rusting.
This method works even if the protective metal layer is damaged, unlike barrier methods. The more reactive metal loses electrons more easily than iron, acting as a reducing agent that donates electrons to any iron that would otherwise oxidise to form rust.
Iron ship hulls are often fitted with blocks of magnesium to prevent rusting. Explain how this works, with reference to the reactivity series.
- 1
Locate magnesium and iron in the reactivity series: magnesium is significantly more reactive than iron.
- 2
When exposed to salt water and oxygen, magnesium corrodes (oxidises) preferentially, losing electrons to form magnesium ions.
- 3
Any iron atom that would lose electrons to form rust immediately gains electrons from the corroding magnesium, so it remains as neutral iron metal and does not rust.
- 4
Magnesium blocks are replaced periodically once they have fully corroded.
5. Common Pitfalls
Wrong move:
Forgetting to include carbon and hydrogen when using the reactivity series
Why:
Carbon is required to predict metal extraction from oxides, and hydrogen is required to predict dilute acid reaction outcomes.
Correct move:
Always memorize the full series including both non-metals in the correct order.
Wrong move:
Stating that all metals react with dilute acids
Why:
Metals below hydrogen (copper, silver, gold) cannot displace hydrogen from dilute acids, so no reaction occurs.
Correct move:
Only predict acid reactions for metals positioned above hydrogen in the reactivity series.
Wrong move:
Using the terms corrosion and rusting interchangeably
Why:
Corrosion is the general breakdown of any metal, while rusting is the specific corrosion of iron only. Other metals like aluminium form protective corrosion layers that stop further damage.
Correct move:
Use rusting exclusively when referring to iron corrosion, and corrosion for all other metals.
Wrong move:
Claiming barrier methods like paint work even if scratched
Why:
Scratches break the barrier, allowing oxygen and water to reach the iron surface, so rusting starts at the scratch site.
Correct move:
Use galvanising or sacrificial protection for objects where the coating may be damaged, as these methods work even if the surface is scratched.
Wrong move:
Stating rusting only requires water or only oxygen
Why:
Both reactants are required for the rusting reaction to proceed; iron will not rust in dry air or deoxygenated water.
Correct move:
Always state that both oxygen (from air) and liquid water are necessary for rusting to occur.
6. Quick Reference Cheatsheet
Concept | Core Rule | Extended Rule |
|---|---|---|
Reactivity Series Order | K > Na > Ca > Mg > Al > C > Zn > Fe > Pb > H > Cu > Ag > Au | More reactive metals are stronger reducing agents, lose electrons more easily |
Dilute Acid Reactions | Metals above H produce salt + Hβ | Reactions are redox: metal oxidised, HβΊ ions reduced |
Displacement Reactions | More reactive metal displaces less reactive metal from its compound | Redox process: more reactive metal is oxidised, less reactive metal ion is reduced |
Rusting Conditions | Requires both Oβ and liquid water | Rusting is redox: Fe oxidised, Oβ reduced |
Rust Prevention | Barrier methods, galvanising, alloying | Sacrificial protection uses Zn/Mg to corrode preferentially and protect Fe |
Metal Extraction | Metals below C extracted by reduction with C; metals above C extracted by electrolysis | Extraction reactions are redox processes |
7. Frequently Asked
Why are carbon and hydrogen included in the reactivity series?
Carbon is a non-metal included to predict metal extraction from oxides: metals below carbon can be extracted by reduction with carbon, while metals above require electrolysis. Hydrogen is included to predict dilute acid reactions: only metals above hydrogen react with dilute acids to produce hydrogen gas.
What is the difference between corrosion and rusting?
Corrosion is the general term for breakdown of any metal by environmental reactions. Rusting is the specific term for corrosion of iron only, producing soft, flaky hydrated iron(III) oxide that exposes more iron to further damage. Other metals like aluminium corrode to form a hard, protective oxide layer that stops further corrosion.
Going deeper
What's Next
Now that you have mastered the reactivity series and corrosion, you are ready to move on to metal extraction processes, which rely entirely on reactivity series rankings to select the correct extraction method for each metal. If you are studying the Extended tier, you can also practice writing ionic half equations for displacement and corrosion reactions to prepare for longer answer questions in Paper 2 and 4. Make sure to test your knowledge with structured practice questions on this topic, as it is frequently examined across both Core and Extended papers.