Metals, redox and electrolysis are tied together by a single idea — the transfer of electrons — and once you read everything through the reactivity series, this topic becomes one of the most predictable in O-Level / SEC Chemistry. Reactions of metals, how they are extracted, why they rust, and what happens at electrodes all follow from how readily a metal loses electrons. This guide is from Ancourage Academy, whose secondary Chemistry tuition teaches redox concept-first in small groups of 3–6 at Bishan and Woodlands.
This is a single-topic deep-dive that complements our O-Level / SEC Chemistry guide and pairs with our acids, bases and salts guide. The mole calculations behind electrolysis come from our mole concept guide, and the same redox ideas scale into JC — see our H2 Chemistry inorganic guide.
If metals, redox or electrolysis are where marks slip, Ancourage Academy's Sec 4 Chemistry programme rebuilds the topic from the reactivity series upward — book a trial class (usually $18) for a diagnostic assessment.
What Do Metals, Redox and Electrolysis Cover?
This topic covers the reactivity series and metal reactions, redox in terms of oxygen and hydrogen, electron transfer and oxidation number, the extraction of metals including iron in the blast furnace, rusting and its prevention, and electrolysis of molten and aqueous electrolytes. The SEAB Chemistry syllabus (6092) sets the requirements, and from 2027 the same content carries into the SEC G3 Chemistry syllabus (K324). The reactivity series is the thread that links every part.
How Does the Reactivity Series Work?
The reactivity series ranks metals by how readily they lose electrons to form positive ions, and this order predicts their reactions with water, acid and oxygen, as well as displacement reactions.
| Reactivity | Example metals | Reaction with dilute acid |
|---|---|---|
| Most reactive | Potassium, sodium, calcium | Vigorous; gives hydrogen |
| Moderate | Magnesium, zinc, iron | Steady; gives hydrogen |
| Least reactive | Copper, silver, gold | Little or no reaction |
A more reactive metal displaces a less reactive one from its compound, because it loses electrons more readily. The series also explains why reactive metals are harder to extract and why unreactive metals such as gold are found uncombined in nature.
How Do Metals React with Water, Acid and Oxygen?
The vigour of a metal's reaction with water, acid and oxygen falls steadily down the reactivity series, which is why these reactions are used to rank the metals.
- With water or steam: reactive metals react with cold water; moderate metals react only with steam; unreactive metals do not react.
- With dilute acid: metals above hydrogen give a salt and hydrogen gas; metals below hydrogen, such as copper, do not.
- With oxygen: most metals form a metal oxide on burning or heating, more readily the higher up the series.
Comparing these reactions across several metals is a classic experiment-design question, so be ready to describe a fair test that ranks the metals.
What Is Redox in Terms of Oxygen, Electrons and Oxidation Number?
Oxidation is the gain of oxygen, loss of hydrogen, loss of electrons, or an increase in oxidation number, while reduction is the loss of oxygen, gain of hydrogen, gain of electrons, or a decrease in oxidation number — and the two always happen together in a redox reaction. An oxidising agent accepts electrons (and is itself reduced), while a reducing agent donates electrons (and is itself oxidised).
- By oxygen: a substance that gains oxygen is oxidised; one that loses oxygen is reduced.
- By hydrogen: a substance that loses hydrogen is oxidised; one that gains hydrogen is reduced.
- By electrons: a useful memory aid is OIL RIG — oxidation is loss, reduction is gain of electrons.
- By oxidation number: an increase in oxidation state is oxidation; a decrease is reduction — useful when there is no obvious oxygen or electron transfer.
- Oxidising agent: brings about oxidation in something else by accepting electrons.
- Reducing agent: brings about reduction in something else by donating electrons.
Identifying which species is oxidised and which is reduced, and naming the agents correctly, is the part most often tested, so practise labelling both halves of a reaction.
How Are Metals Extracted from Their Ores?
The method used to extract a metal depends on its position in the reactivity series: very reactive metals are extracted by electrolysis, while moderately reactive metals such as iron are reduced by carbon. Iron is extracted in the blast furnace, where carbon and carbon monoxide reduce iron oxide to molten iron, and limestone removes impurities as slag. Unreactive metals such as gold need little or no extraction because they occur uncombined. Linking the method to reactivity is the key marking point.
What Causes Rusting and How Is It Prevented?
Rusting is the corrosion of iron, which needs both oxygen and water to occur, and it is prevented by keeping these out or by sacrificial protection.
- Conditions: rusting requires both water and oxygen — removing either prevents it.
- Barrier methods: painting, oiling, greasing or plastic coating keep out air and water.
- Sacrificial protection: attaching a more reactive metal, such as zinc, which corrodes instead of the iron.
- Galvanising: coating iron with zinc combines a barrier with sacrificial protection.
Sacrificial protection is a favourite question because it links rusting back to the reactivity series — the protecting metal must be more reactive than iron.
How Does Electrolysis Work at the Electrodes?
Electrolysis uses electricity to break down a molten or aqueous ionic compound, with positive ions discharged at the cathode and negative ions at the anode; for aqueous solutions, selective discharge decides which ion reacts.
| Electrolyte | At the cathode | At the anode |
|---|---|---|
| Molten compound | Metal is deposited | Non-metal is released |
| Aqueous (general) | Less reactive cation, else hydrogen | Halide if concentrated, else oxygen |
In aqueous solutions, the cation lower in the reactivity series is usually discharged in preference to hydrogen, and a halide ion in a concentrated solution is usually discharged in preference to producing oxygen, though a dilute halide solution gives oxygen from water instead. Electrolysis is applied in electroplating, where an object is coated with metal, and in the purification of copper, where an impure anode dissolves and pure copper deposits on the cathode. At O-Level / SEC the focus is on predicting the electrode products and writing the electrode half-equations rather than calculating quantities from charge.
The Most Common Metals and Electrolysis Mistakes
In our Chemistry classes at Ancourage Academy, a handful of recurring errors cause most avoidable mark loss in these topics.
| Mistake | Why it happens | How to fix it |
|---|---|---|
| Mixing up oxidation and reduction | Forgetting the electron definition | Use OIL RIG: oxidation is loss, reduction is gain of electrons |
| Wrong electrode product | Ignoring selective discharge | Apply the discharge rules for aqueous solutions |
| Confusing anode and cathode | Forgetting the charge signs | Cathode is negative (cations go there); anode is positive |
| Wrong extraction method | Not linking to reactivity | Electrolysis for reactive metals, carbon reduction for iron |
| Forgetting a rusting condition | Naming only oxygen or only water | Rusting needs both oxygen and water present |
A Study Plan for Metals, Redox and Electrolysis
Work this topic in order: the reactivity series, then redox, then extraction and rusting, then electrolysis.
- Week 1 — reactivity series: learn the order and the reactions with water, acid and oxygen.
- Week 2 — redox: drill oxidation and reduction by oxygen and by electrons, and name the agents.
- Week 3 — extraction and rusting: link extraction method to reactivity and master rusting prevention.
- Week 4 — electrolysis: practise selective discharge, electroplating, purification, and timed past-paper questions.
Ancourage Academy's Sec 3 and Sec 4 Chemistry programmes work through these topics on this progression in small groups of 3–6. Book a trial class (usually $18) for a diagnostic, or WhatsApp us with any questions.
Common Questions About O-Level / SEC Chemistry Metals and Electrolysis
What is the reactivity series and why does it matter?
The reactivity series is a ranking of metals by how readily they lose electrons to form positive ions. It matters because it predicts behaviour across the whole topic: how vigorously a metal reacts with water, acid and oxygen, whether one metal will displace another from its compound, how the metal must be extracted from its ore, and which ion is discharged during electrolysis. Reading every metal question through the reactivity series turns separate facts into one consistent pattern.
How do you define oxidation and reduction?
Oxidation is the gain of oxygen, the loss of hydrogen, the loss of electrons, or an increase in oxidation number, and reduction is the loss of oxygen, the gain of hydrogen, the gain of electrons, or a decrease in oxidation number. The two always occur together in a redox reaction, since electrons lost by one species are gained by another. A useful memory aid is OIL RIG: oxidation is loss, reduction is gain of electrons. The oxidising agent accepts electrons and is reduced, while the reducing agent donates electrons and is oxidised.
How is iron extracted in the blast furnace?
Iron is extracted by reduction with carbon because it sits in the middle of the reactivity series. In the blast furnace, coke burns to form carbon dioxide, which reacts with more carbon to make carbon monoxide; this carbon monoxide reduces iron oxide to molten iron that runs to the bottom. Limestone is added to remove sandy impurities, forming slag that floats on the iron. Metals above carbon in the reactivity series, such as aluminium, cannot be extracted by carbon reduction and need electrolysis instead.
Why are different products formed during electrolysis of aqueous solutions?
In aqueous solutions, water also provides hydrogen and hydroxide ions, so selective discharge decides which ion reacts at each electrode. At the cathode, the less reactive cation is usually discharged in preference to hydrogen, so a reactive-metal ion stays in solution while hydrogen is released. At the anode, a halide ion is usually discharged in preference to oxygen when the solution is concentrated, but a dilute halide solution (or one containing sulfate or nitrate ions) gives oxygen from water instead. This is why the products often differ from those of the same compound when molten.
Related: All O-Level Chemistry topics · Acids, Bases and Salts · Choosing Combined vs Pure Science · H2 Chemistry Inorganic · O-Level / SEC Chemistry guide · O-Level / SEC Chemistry guide