Reactivity Series Predictions
Using the reactivity series to predict reactions in IGCSE Chemistry: displacement, extraction methods, reactions with water and acid, and exam strategies for Cambridge 0620.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
The reactivity series is one of the most powerful predictive tools in the Cambridge 0620 syllabus. Knowing the order of metals and understanding the patterns it reveals allows candidates to predict outcomes across several topics: displacement, extraction, corrosion, and reactions with water and acids.
The reactivity series
Most reactive to least reactive:
K > Na > Ca > Mg > Al > (C) > Zn > Fe > (H) > Cu > Ag > Au
Carbon and hydrogen are included as reference points, not because they are metals.
Prediction 1: Reactions with water
| Metal | Reaction with cold water | Reaction with steam |
|---|---|---|
| Potassium | Vigorous — floats, moves, lilac flame, melts | — |
| Sodium | Vigorous — floats, moves, may ignite | — |
| Calcium | Steady fizzing | — |
| Magnesium | Very slow with cold water | Vigorous with steam: Mg + H₂O → MgO + H₂ |
| Aluminium | No reaction (oxide layer) | Reacts with steam |
| Zinc | No reaction | Slow with steam |
| Iron | No reaction | Slow with steam: 3Fe + 4H₂O → Fe₃O₄ + 4H₂ |
| Copper to gold | No reaction | No reaction |
Pattern: more reactive metals react with cold water; moderately reactive metals react with steam; unreactive metals do not react with water at all.
Prediction 2: Reactions with dilute acid
Metals above hydrogen in the reactivity series react with dilute hydrochloric or sulfuric acid to produce a salt and hydrogen.
| Metal | Reaction with dilute HCl | Observation |
|---|---|---|
| Magnesium | Mg + 2HCl → MgCl₂ + H₂ | Very vigorous fizzing, rapid dissolving |
| Zinc | Zn + 2HCl → ZnCl₂ + H₂ | Steady fizzing |
| Iron | Fe + 2HCl → FeCl₂ + H₂ | Slow fizzing, solution turns green |
| Copper | No reaction | Nothing happens |
| Silver | No reaction | Nothing happens |
Pattern: the higher the metal in the series, the more vigorous the reaction. Metals below hydrogen do not react with dilute acid.
Note: potassium, sodium, and calcium are too reactive to be safely tested with acid — the reactions would be dangerously vigorous.
Prediction 3: Displacement reactions
A more reactive metal displaces a less reactive metal from a solution of its salt.
Rule: the free metal must be above the metal in the compound.
| Prediction | Equation | Occurs? |
|---|---|---|
| Zn + CuSO₄ | Zn + CuSO₄ → ZnSO₄ + Cu | Yes (Zn above Cu) |
| Fe + ZnSO₄ | Fe + ZnSO₄ → ? | No (Fe below Zn) |
| Mg + FeSO₄ | Mg + FeSO₄ → MgSO₄ + Fe | Yes (Mg above Fe) |
| Cu + AgNO₃ | Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag | Yes (Cu above Ag) |
Prediction 4: Extraction method
| Position in series | Extraction method | Examples |
|---|---|---|
| Above carbon (K, Na, Ca, Mg, Al) | Electrolysis of molten compound | Aluminium from Al₂O₃ |
| Below carbon but above hydrogen (Zn, Fe) | Reduction with carbon/coke | Iron from Fe₂O₃ in a blast furnace |
| Below hydrogen (Cu, Ag, Au) | Found native or reduced easily | Gold found as the element; copper from roasting CuS |
Pattern: the more reactive the metal, the harder (more energy-intensive) it is to extract.
Prediction 5: Corrosion tendency
More reactive metals corrode more readily. Iron corrodes (rusts) when exposed to water and oxygen. Gold and platinum do not corrode because they are very unreactive.
This also predicts sacrificial protection: a more reactive metal (e.g. zinc) corrodes instead of a less reactive metal (e.g. iron) when they are in contact.
Prediction 6: Stability of compounds
Compounds of more reactive metals are more thermally stable. This explains why:
- Sodium carbonate does not decompose at Bunsen temperatures
- Copper carbonate decomposes easily (CuCO₃ → CuO + CO₂)
Using the reactivity series in exam questions
Common question patterns:
- “Predict whether a reaction will occur between X and Y” — compare positions in the series
- “Explain why metal A is extracted by electrolysis but metal B by carbon reduction” — refer to positions relative to carbon
- “Place these metals in order of reactivity based on experimental data” — use reaction vigour with acid or water to rank them
- “Explain why zinc protects iron from rusting” — zinc is more reactive, so it corrodes preferentially
Worked exam question
Four metals P, Q, R, and S are tested. P reacts slowly with steam but not cold water. Q reacts vigorously with cold water. R does not react with water or dilute acid. S reacts moderately with dilute acid. Place the metals in order of decreasing reactivity. [2]
Q (reacts with cold water — most reactive) > P (reacts with steam) > S (reacts with dilute acid but not water) > R (does not react — least reactive) [2]
Common exam mistakes
- Predicting displacement in the wrong direction — the free metal must be MORE reactive than the metal in the compound.
- Saying aluminium “does not react” because it appears unreactive in everyday life — aluminium IS reactive but has a protective oxide layer. In experiments where the oxide is removed, aluminium reacts vigorously.
- Forgetting that carbon and hydrogen are reference points, not metals. They help predict extraction methods and acid reactions.
- Writing copper reacts with dilute HCl — copper is below hydrogen in the series and does not react with dilute acids.
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