What is the Reactivity Series in Chemistry?

The Reactivity Series is a list of metals arranged in order of their reactivity from highest to lowest. It is an essential concept in Inorganic Chemistry, particularly for the Edexcel IGCSE curriculum, as it helps predict how metals will react with acids, water, and other substances.

How is the Reactivity Series used to predict reactions in Edexcel IGCSE Chemistry?

In Edexcel IGCSE Chemistry, the Reactivity Series is used to predict the outcomes of reactions involving metals. For example, a more reactive metal can displace a less reactive metal from its compound. This principle is applied in displacement reactions and helps in understanding the extraction of metals.

Why are some metals more reactive than others in the Reactivity Series?

The reactivity of metals in the Reactivity Series is determined by their ability to lose electrons and form positive ions. Metals that lose electrons more easily are more reactive. Factors such as atomic structure and the energy required to remove electrons influence a metal's reactivity.

Can you explain how the Reactivity Series affects metal extraction processes?

The Reactivity Series plays a crucial role in determining the method used for metal extraction. Highly reactive metals, like potassium and sodium, are extracted through electrolysis, while less reactive metals, such as iron, can be extracted by reduction with carbon. This is because more reactive metals form stronger bonds with other elements, requiring more energy to break.

What are some common examples of displacement reactions involving the Reactivity Series?

Displacement reactions occur when a more reactive metal displaces a less reactive metal from its compound. For instance, when zinc is added to copper sulfate solution, zinc displaces copper, forming zinc sulfate and copper metal. This is a typical example studied in Edexcel IGCSE Chemistry to illustrate the concept of the Reactivity Series.

Why is "Predicting that a LESS reactive metal can displace a MORE reactive one (e.g. Cu can displace Zn)" a common mistake in Reactivity Series?

Why it happens: Not understanding which way the electron flow needs to go. How to avoid it: The MORE reactive metal loses electrons more easily, so it does the displacing. Order: in 'Zn + CuSO₄', Zn is MORE reactive → Zn displaces Cu (yes reaction). In 'Cu + ZnSO₄', Cu is LESS reactive → no reaction. Check the series: the metal that's HIGHER in the list wins. Source: 4CH1 Examiner Reports 2022-2024

Why is "Mixing up oxidation and reduction with OIL RIG" a common mistake in Reactivity Series?

Why it happens: Remembering OIL RIG but applying it the wrong way. How to avoid it: **OIL** = **O**xidation **I**s **L**oss (of electrons). **RIG** = **R**eduction **I**s **G**ain (of electrons). The reaction happens TO the species ITSELF — not 'the agent'. Mg → Mg²⁺ + 2e⁻: Mg loses e⁻ → Mg is OXIDISED (= itself oxidised; Mg is the reducing agent).

Why is "Confusing the roles of the three test tubes in the rusting experiment" a common mistake in Reactivity Series?

Why it happens: Not understanding what each variable controls. How to avoid it: Tube A: water + O₂ (positive control — rusts). Tube B: water but NO O₂ (boiled + oil — proves O₂ needed). Tube C: O₂ but NO water (CaCl₂ removes moisture — proves water needed). Outcome: A rusts; B and C don't. Conclusion: BOTH O₂ AND water needed. Source: 4CH1 Examiner Reports 2023-2024

Why is "Saying that galvanising fails as soon as the coating is scratched" a common mistake in Reactivity Series?

Why it happens: Thinking that a barrier only works if intact. How to avoid it: Galvanising provides TWO mechanisms: barrier + sacrificial protection. Even if scratched, the surrounding ZINC is more reactive than iron → it oxidises preferentially (Zn → Zn²⁺ + 2e⁻). So the iron stays protected. Contrast with TIN-plating: if scratched, tin is LESS reactive than iron → iron rusts faster. Source: 4CH1 Examiner Reports 2022-2024

Why is "Stating that 'zinc doesn't rust' as the reason for galvanising" a common mistake in Reactivity Series?

Why it happens: Confusing 'doesn't rust' (no reaction with O₂ and H₂O) with 'protects iron' (provides electrons). How to avoid it: Zinc DOES corrode (forms ZnO and Zn(OH)₂); it just corrodes preferentially because it's more reactive. The point of galvanising is that the zinc's corrosion SHIELDS the iron beneath — not that zinc is itself uncorrodible.

Why is "Identifying only some redox reactions as 'redox' (e.g. excluding combustion)" a common mistake in Reactivity Series?

Why it happens: Associating redox only with metal-displacement contexts. How to avoid it: REDOX = ANY reaction involving electron transfer / oxidation state change. Includes: combustion (Mg + O₂ → MgO), displacement (Fe + Cu²⁺ → Fe²⁺ + Cu), thermal reduction (CuO + C → Cu + CO), electrolysis (cathode + anode reactions). All of these are redox.

Inorganic ChemistryEdexcel IGCSE Chemistry (4CH1)

Reactivity Series

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Reactivity Series — Pearson Edexcel International GCSE Chemistry 4CH1 Study Notes (2026 onwards, Spec Issue 4)

Ordering metals by their tendency to lose electrons. Standard 4CH1 series: K > Na > Ca > Mg > Al > (C) > Zn > Fe > (H) > Cu > Ag > Au. The series predicts reactions with water, acid, and metal-ion solutions (displacement). Redox defined in terms of oxygen AND electrons (OIL RIG). Iron rusts only when BOTH water AND oxygen are present — preventable by barrier, sacrificial protection, or galvanising.

At a glance

Standard 4CH1 reactivity series: K > Na > Ca > Mg > Al > (C) > Zn > Fe > (H) > Cu > Ag > Au.
Carbon and hydrogen included as REFERENCE points — they determine extraction methods.
Mnemonic: 'Please Stop Calling Me A Careless Zebra Instead Try Learning How Copper Saves Gold'.
Cold water test: only K, Na, Ca react (vigorously); Mg slowly; everything below = no reaction.
Dilute HCl test: metals ABOVE H displace H₂; metals BELOW H (Cu, Ag, Au) do NOT react.
Displacement: MORE reactive metal displaces LESS reactive from solution (e.g. Fe + CuSO₄ → FeSO₄ + Cu).
Redox: Oxidation = LOSS of e⁻ (or gain of O); Reduction = GAIN of e⁻ (or loss of O). Mnemonic OIL RIG.
Rusting requires BOTH water AND oxygen. Hydrated iron(III) oxide forms.
Prevention: paint (barrier); galvanising (Zn — barrier + sacrificial); sacrificial blocks (Zn/Mg).

What you’ll learn

Mapped to the Cambridge IGCSE 4CH1 syllabus (2026 onwards).

2.14 — Understand that the reactivity series of metals is a list of metals (and the non-metals carbon and hydrogen) in order of their reactivity.
2.15 — Place metals K, Na, Ca, Mg, Al, Zn, Fe, Cu, Ag, Au and the non-metals C and H in the correct order based on their reactions with water, acid and oxygen.
2.16 — Predict the products of displacement reactions between metals and aqueous solutions of metal salts, given the reactivity series.
2.17 — Define oxidation as gain of oxygen OR loss of electrons; reduction as loss of oxygen OR gain of electrons.
2.18 — Identify the species being oxidised and reduced in redox reactions.
2.19 — Understand the terms 'oxidising agent' and 'reducing agent' (a species that brings about oxidation/reduction is itself reduced/oxidised).
2.20 — Describe the conditions necessary for iron to rust (presence of both water AND oxygen).
2.21 — Describe the methods used to prevent rusting (barrier methods, sacrificial protection, galvanising).

The reactivity series — order and how it's built (spec 2.14, 2.15)

K > Na > Ca > Mg > Al > (C) > Zn > Fe > (H) > Cu > Ag > Au. Order determined by reactions with water, acid, oxygen.

The standard 4CH1 reactivity series.

K > Na > Ca > Mg > Al > (C) > Zn > Fe > (H) > Cu > Ag > Au

Mnemonic. "Please Stop Calling Me A Careless Zebra Instead Try Learning How Copper Saves Gold." — Potassium, Sodium, Calcium, Magnesium, Aluminium, Carbon, Zinc, Iron, Tin, Lead, Hydrogen, Copper, Silver, Gold.

Each metal is placed by examining its observed reactions with three reagents: water (cold and as steam), dilute acid (HCl or H₂SO₄), and oxygen. A metal that reacts more vigorously than another is placed higher.

Test 1 — Reactions with cold water.

Metal	Observation	Reaction
K	Reacts VIOLENTLY; ignites with lilac flame	2K + 2H₂O → 2KOH + H₂
Na	Vigorous; melts into ball; moves on surface	2Na + 2H₂O → 2NaOH + H₂
Ca	Steady fizz; cloudy Ca(OH)₂ forms	Ca + 2H₂O → Ca(OH)₂ + H₂
Mg	Very slow with cold water (faster with STEAM)	Mg + H₂O → MgO + H₂ (steam)
Al, Zn, Fe, Cu, Ag, Au	No visible reaction with cold water	—

So the cold-water test only distinguishes the top few — K, Na, Ca.

Test 2 — Reactions with dilute HCl.

Metal	Observation
K, Na, Ca	Reacts EXPLOSIVELY — dangerous; not normally tested
Mg	Reacts vigorously — strong fizz; H₂ pops
Al	Reacts slowly (oxide layer needs to be removed first); then vigorously
Zn	Reacts steadily — fizz
Fe	Reacts slowly — gentle fizz; pale green FeCl₂ solution
Cu, Ag, Au	NO reaction — below H in the series

General equation: M + nHCl → MClₙ + (n/2)H₂. Only works for metals ABOVE H.

Test 3 — Reactions with oxygen.

Metal	Observation
K, Na	Burn vigorously with characteristic flames (red, yellow)
Mg	Burns brilliant WHITE light → white MgO
Al	Slow oxidation forms protective Al₂O₃
Zn, Fe	Slowly form oxide with heat
Cu	Slowly forms black CuO on heating
Ag, Au	Au does not oxidise; Ag tarnishes very slowly

Why this order? Reactivity = how readily a metal LOSES its outer electron(s) to form a positive ion. Metals at the top (K, Na) lose electrons most easily (low ionisation energies, weak hold on outer electrons). Metals at the bottom (Au, Ag, Pt) hold their electrons tightly and rarely lose them.

Where carbon and hydrogen fit. Carbon and hydrogen are NOT metals, but they fit into the series at specific positions based on which metals they can REDUCE:

Carbon is BETWEEN Al and Zn. It can reduce ZnO, FeO, CuO etc. (carbon-reduction extraction), but NOT Al₂O₃ or higher.
Hydrogen is BETWEEN Fe and Cu. It can reduce CuO, AgO, but NOT FeO (in practice).

These reference points are crucial for choosing extraction methods (next subtopic).

Series order: K > Na > Ca > Mg > Al > (C) > Zn > Fe > (H) > Cu > Ag > Au.
Test 1: cold water reactions (only top of series).
Test 2: dilute HCl reactions (metals above H).
Test 3: oxygen reactions (intensity of burning).
C and H are reference points for extraction methods.

See the full worked example for reactivity series →

Displacement reactions (spec 2.16)

More reactive metal displaces less reactive metal from a solution of its salt. Used to determine ordering.

The principle. A more reactive metal DISPLACES a less reactive metal from a compound or solution. In ionic terms, the more reactive metal preferentially loses electrons; the less reactive ion preferentially gains them.

Classic example — iron in copper(II) sulfate.

Equation:

$\text{Fe(s)} + \text{CuSO}_4\text{(aq)} \rightarrow \text{FeSO}_4\text{(aq)} + \text{Cu(s)}$

Ionic equation (SO₄²⁻ is the spectator ion):

$\text{Fe(s)} + \text{Cu}^{2+}\text{(aq)} \rightarrow \text{Fe}^{2+}\text{(aq)} + \text{Cu(s)}$

Observations:

Blue colour of CuSO₄ FADES (Cu²⁺ being removed); replaced by pale green colour of Fe²⁺.
Pink-brown coating of copper forms on the iron nail.
Iron gradually dissolves into the solution.

Half-equations (showing electron transfer):

Oxidation: Fe → Fe²⁺ + 2e⁻ (iron loses electrons → oxidised).
Reduction: Cu²⁺ + 2e⁻ → Cu (Cu²⁺ gains electrons → reduced).

Two electrons transferred from each Fe atom to each Cu²⁺ ion.

The reverse reaction does NOT happen. Cu(s) + FeSO₄(aq) → no reaction (because Cu is less reactive than Fe; Cu cannot give electrons to Fe²⁺).

Other examples.

Reaction	Outcome	Why
Mg + ZnSO₄ → MgSO₄ + Zn	Reaction occurs	Mg > Zn
Zn + MgSO₄	No reaction	Zn < Mg
Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag	Reaction occurs	Cu > Ag — silvery deposit on Cu wire
Ag + CuSO₄	No reaction	Ag < Cu
Mg + 2HCl → MgCl₂ + H₂	Reaction occurs	Mg > H (displaces H)
Cu + HCl	No reaction	Cu < H

Determining a position in the series from displacement.

If you have an unknown metal X and want to know where it sits, test it against solutions of known-metal salts:

Does X react with CuSO₄? → If yes, X > Cu.
Does X react with FeSO₄? → If yes, X > Fe.
Does X react with MgSO₄? → If yes, X > Mg.
... and so on.

By comparing the pattern of yes/no, you can place X at the correct position. This is the basis of the required practical for determining a reactivity series experimentally.

Thermite reaction (extension). A classic high-temperature displacement: aluminium displaces iron from iron(III) oxide:

$2\text{Al(s)} + \text{Fe}_2\text{O}_3\text{(s)} \rightarrow 2\text{Fe(l)} + \text{Al}_2\text{O}_3\text{(s)} + \text{heat}$

The reaction is so exothermic that molten iron is produced — used historically for welding railway tracks. Al is more reactive than Fe → Al gives electrons to Fe³⁺.

MORE reactive metal displaces LESS reactive metal from solution / compound.
Classic example: Fe + CuSO₄ → FeSO₄ + Cu (blue fades; Cu deposits).
Ionic equation removes spectator ions (here, SO₄²⁻).
Reverse never works: less reactive can't displace more reactive.
Thermite: 2Al + Fe₂O₃ → 2Fe + Al₂O₃ (welding rails).

See the full worked example for reactivity series →

Oxidation and reduction — oxygen AND electron definitions (spec 2.17, 2.18, 2.19)

Oxidation = gain of O / loss of e⁻. Reduction = loss of O / gain of e⁻. OIL RIG.

Two equivalent definitions.

Edexcel asks you to know BOTH ways of defining oxidation and reduction:

Process	Oxygen definition	Electron definition
Oxidation	GAIN of oxygen	LOSS of electrons
Reduction	LOSS of oxygen	GAIN of electrons

Mnemonic: OIL RIG — Oxidation Is Loss (of electrons); Reduction Is Gain (of electrons).

Why two definitions?

The OXYGEN definition is HISTORICAL — early chemists studied metal oxides and saw 'gain of oxygen' as a unifying theme.
The ELECTRON definition is MORE GENERAL — it works for reactions that don't involve oxygen at all (e.g. Mg + Cl₂ → MgCl₂ is redox, but no oxygen present).

Both definitions usually agree, but the electron definition is preferred for understanding mechanism.

Example 1 — Reaction with oxygen.

$2\text{Mg(s)} + \text{O}_2\text{(g)} \rightarrow 2\text{MgO(s)}$

Oxygen definition:

Mg gains oxygen → Mg is OXIDISED.
(O₂ loses 'oxygen' from being separate to being combined → O is REDUCED.)

Electron definition:

Mg → Mg²⁺ + 2e⁻ (Mg loses e⁻ → OXIDISED).
O₂ + 4e⁻ → 2O²⁻ (O₂ gains e⁻ → REDUCED).

Both definitions agree: Mg is oxidised; O₂ is reduced.

Example 2 — Reaction with no oxygen.

$\text{Mg(s)} + \text{Cl}_2\text{(g)} \rightarrow \text{MgCl}_2\text{(s)}$

Oxygen definition: doesn't apply (no oxygen present).

Electron definition:

Mg → Mg²⁺ + 2e⁻ (Mg loses e⁻ → OXIDISED).
Cl₂ + 2e⁻ → 2Cl⁻ (Cl₂ gains e⁻ → REDUCED).

The electron definition correctly identifies this as a redox reaction even though oxygen isn't involved.

Example 3 — Displacement.

$\text{Fe(s)} + \text{Cu}^{2+}\text{(aq)} \rightarrow \text{Fe}^{2+}\text{(aq)} + \text{Cu(s)}$

Electron definition:

Fe → Fe²⁺ + 2e⁻ (Fe loses e⁻ → OXIDISED).
Cu²⁺ + 2e⁻ → Cu (Cu²⁺ gains e⁻ → REDUCED).

Oxidising agents and reducing agents.

The oxidising agent is the species that BRINGS ABOUT oxidation of something else. It does so by ACCEPTING electrons from the other species. So the oxidising agent is ITSELF reduced.
The reducing agent is the species that BRINGS ABOUT reduction of something else. It DONATES electrons to the other species. So the reducing agent is ITSELF oxidised.

In Mg + Cl₂ → MgCl₂:

Cl₂ is the OXIDISING AGENT (takes electrons from Mg; itself reduced).
Mg is the REDUCING AGENT (gives electrons to Cl₂; itself oxidised).

Practice tip. Always remember: the agent does the OPPOSITE of its name to itself. Oxidising agent → itself reduced. Reducing agent → itself oxidised.

Common oxidising agents. O₂, Cl₂, Br₂, H₂SO₄, KMnO₄, K₂Cr₂O₇, HNO₃. Common reducing agents. Reactive metals (Mg, Zn, Fe), C, CO, H₂.

Oxidation = gain of O / loss of e⁻. Reduction = loss of O / gain of e⁻.
OIL RIG: Oxidation Is Loss; Reduction Is Gain (of electrons).
Electron definition more general — applies even without O.
Oxidising agent: itself reduced (accepts e⁻).
Reducing agent: itself oxidised (donates e⁻).

See the full worked example for reactivity series →

Rusting of iron — conditions and prevention (spec 2.20, 2.21)

Iron rusts only when BOTH water AND oxygen are present. Prevent by barrier, sacrificial, or galvanising.

What is rust? A flaky orange-brown solid — hydrated iron(III) oxide, Fe₂O₃·xH₂O. Forms on iron and steel surfaces exposed to the atmosphere.

Conditions required.

For iron to rust, BOTH water AND oxygen must be present:

$4\text{Fe(s)} + 3\text{O}_2\text{(g)} + x\text{H}_2\text{O(l)} \rightarrow 2\text{Fe}_2\text{O}_3 \cdot x\text{H}_2\text{O(s)}$

If either is absent, rusting does not occur. This is demonstrated by the classic three test-tube experiment (required practical):

Tube	Contents	Outcome	Why
A	Iron nail + tap water + air	RUSTS	Both water and O₂ present
B	Iron nail + boiled water + oil layer on top	NO rust	Water but NO O₂ (boiled out + sealed by oil)
C	Iron nail + anhydrous CaCl₂ (dries the air)	NO rust	O₂ but NO water

Conclusion: Both water AND O₂ are required for rusting.

Mechanism of rusting (extension). Rusting is an ELECTROCHEMICAL process — like a tiny battery on the surface of the iron:

Iron is OXIDISED: Fe → Fe²⁺ + 2e⁻
Oxygen is REDUCED (in the presence of water): O₂ + 2H₂O + 4e⁻ → 4OH⁻
Fe²⁺ + 2OH⁻ → Fe(OH)₂, which then oxidises to Fe(OH)₃, finally dehydrating to Fe₂O₃·xH₂O (rust).

Salt water accelerates rusting (ions improve the conductivity of the surface 'electrolyte').

Why rusting is a problem. Rust is FLAKY and DOESN'T adhere well to the iron beneath — unlike the tough Al₂O₃ layer on aluminium. So rust falls off and exposes fresh iron, which rusts further → over time, the iron is completely consumed. Rusted bridges, cars, pipes can fail catastrophically. Estimated cost of corrosion worldwide: 2-4% of GDP.

Prevention methods.

Method 1 — Barrier methods (paint, oil, grease, plastic, plating).

What it does. Physical layer prevents O₂ and H₂O reaching the iron surface.
Examples. Paint on cars, bicycles, railings; oil/grease on tools and machine parts; powder-coated plastic on garden furniture; tin-plating on food cans; chrome-plating on taps and bumpers.
Limitation. If the coating is SCRATCHED, exposed iron rusts in that spot. Worse: with TIN-plating or CHROME-plating (less reactive than Fe), if scratched the iron rusts even FASTER because the unreactive coating acts as a 'cathode' to the exposed iron 'anode'.

Method 2 — Sacrificial protection (zinc or magnesium blocks).

What it does. A piece of a MORE REACTIVE metal is attached (in electrical contact) to the iron. The reactive metal preferentially loses electrons (Zn → Zn²⁺ + 2e⁻), corroding instead of the iron.
Examples. Zinc blocks bolted to ship hulls (replaced every few years); magnesium 'anodes' on buried iron oil pipelines and inside domestic hot-water tanks.
Mechanism. Even when the iron is exposed to O₂ and H₂O, the electrons supplied by the sacrificial metal keep the iron 'cathodic' — it does not lose its own electrons.
Limitation. Sacrificial metal is consumed and must be REPLACED periodically.

Method 3 — Galvanising (zinc coating).

What it does. Coats iron/steel with a thin layer of zinc, usually by HOT-DIPPING in molten zinc.
Dual mechanism. Operates by TWO methods simultaneously: (1) BARRIER — Zn coat prevents O₂/H₂O from reaching iron; (2) SACRIFICIAL — if scratched, the surrounding Zn corrodes preferentially (Zn > Fe in reactivity series), still protecting the iron.
Examples. Galvanised steel nails, roof sheeting, chain-link fencing, dustbins, motorway crash barriers, gas pipes.
Why it's better than paint. The dual mechanism means a small scratch doesn't lead to catastrophic rusting under the coating.

Method 4 — Less reactive metal plating (tin, chromium, nickel).

What it does. Pure barrier coating with a less reactive metal. Tin on food cans; chromium on taps; nickel on cutlery.
Limitation. OPPOSITE behaviour to galvanising when scratched: the iron now corrodes FASTER because the coating is a cathode and the exposed iron is the anode (sacrificial in reverse).

Comparison summary.

Method	Barrier?	Sacrificial?	Best for
Paint / oil	Yes	No	Cars, large structures
Galvanising	Yes	Yes (if scratched)	Roofs, fencing, nails
Sacrificial blocks	No	Yes	Ships, pipelines, tanks
Tin / Cr plating	Yes	No (worse if scratched)	Food cans, decorative

Rusting requires BOTH water AND oxygen.
Rust = hydrated iron(III) oxide, Fe₂O₃·xH₂O.
Three test-tube experiment proves both needed.
Barrier methods: paint, oil, plastic — physical layer.
Sacrificial protection: more reactive metal (Zn/Mg) corrodes instead.
Galvanising = barrier + sacrificial (best general solution).

See the full worked example for reactivity series →

How it’s examined

Reactivity series is one of the most-tested 4CH1 topics — appears on EVERY paper for combined 8-15 marks per session. Paper 1 (4CH1/1C) items: (a) order metals from observations (3-5 marks); (b) predict displacement reactions + write balanced equations (4-6 marks); (c) define oxidation and reduction in two ways (3-4 marks); (d) describe rusting prevention methods (4-6 marks). Paper 2 (4CH1/2C) extension: (e) explain why sacrificial protection works using e⁻ transfer (4-5 marks); (f) compare four corrosion prevention methods (5-6 marks); (g) identify oxidising and reducing agents (3-4 marks). The three-tube rusting experiment is a frequent required-practical question.

Sources: Pearson Edexcel International GCSE Chemistry 4CH1 specification — Issue 4, September 2024 (valid for 2026 onwards); Pearson Edexcel 4CH1 Examiner Reports 2022-2024; 4CH1/1C May/Jun 2024 question paper and mark scheme; 4CH1/1C January 2024 question paper and mark scheme; 4CH1/1CR January 2024 question paper and mark scheme; 4CH1/2C May/Jun 2024 question paper and mark scheme; 4CH1/2C January 2024 question paper and mark scheme. Last reviewed 2026-05-12.

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Step-by-step worked examples — Reactivity Series

Step-by-step solutions to past-paper-style questions on reactivity series, written exactly the way a tutor would explain them at the board.

1Iron nail in copper(II) sulfate — displacement reaction (5 marks, Paper 1)
Core• Adapted from 4CH1/1C May/Jun 2024 Q4• displacement, reactivity series, ionic equation, spec-2.16
Question
An iron nail is placed in a beaker of blue copper(II) sulfate solution. (a) Predict the observations. (b) Write the balanced symbol equation including state symbols. (c) Write an ionic equation showing the electrons transferred. (d) Explain WHY the reaction occurs. (5 marks)
Step-by-step solution
1. Step 1
  Observations (1 A). (i) Blue colour of the solution gradually fades and turns pale green (Fe²⁺ ions are pale green in solution). (ii) Pink-brown coating of copper metal forms on the iron nail. (iii) Some iron may visibly dissolve. (iv) Beaker may feel slightly warm (exothermic).
2. Step 2
  Balanced equation (1 A). Iron displaces copper from copper(II) sulfate.
  $\text{Fe(s)} + \text{CuSO}_4\text{(aq)} \rightarrow \text{FeSO}_4\text{(aq)} + \text{Cu(s)}$
3. Step 3
  Ionic equation (1 A). SO₄²⁻ is a spectator ion (appears unchanged on both sides), so it cancels:
  $\text{Fe(s)} + \text{Cu}^{2+}\text{(aq)} \rightarrow \text{Fe}^{2+}\text{(aq)} + \text{Cu(s)}$
4. Step 4
  Why it occurs (1 B). Iron is MORE REACTIVE than copper. The Fe atom loses 2 electrons more readily than the Cu²⁺ ion can hold them. The 2 electrons are transferred FROM Fe (oxidised) TO Cu²⁺ (reduced).
  $\text{Fe} \rightarrow \text{Fe}^{2+} + 2e^- \text{ (oxidation)};\quad \text{Cu}^{2+} + 2e^- \rightarrow \text{Cu} \text{ (reduction)}$
5. Step 5
  Conclusion (1 B). This is a REDOX reaction. The more reactive metal (Fe) displaces the less reactive metal (Cu) from solution. Practical use: provides a simple test for whether one metal is more reactive than another; reverse experiment (Cu in FeSO₄) would show NO reaction.
Answer
(a) Blue solution turns pale green; pink-brown Cu deposit on nail; iron dissolves. (b) Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s). (c) Fe + Cu²⁺ → Fe²⁺ + Cu. (d) Fe is more reactive than Cu — Fe loses 2e⁻ (oxidation) to Cu²⁺ which gains 2e⁻ (reduction). The reverse reaction (Cu in FeSO₄) would NOT occur.
Examiner tip
Edexcel 5-mark mark scheme: 1 for valid observations (must include both colour change AND deposit); 1 for balanced equation with state symbols; 1 for ionic equation (no spectator ions); 1 for stating Fe is more reactive than Cu; 1 for identifying redox (electron transfer). Common error: not eliminating spectator ions for ionic equation. SO₄²⁻ is unchanged → cancels.
2Required practical: investigating rusting of iron (6 marks, Paper 1)
Core• Adapted from 4CH1/1C Jan 2024 Q6• rusting, required practical, iron, spec-2.20, spec-2.21
Question
An investigation is set up using three test tubes to find out the conditions needed for iron to rust. Tube A contains an iron nail and tap water; Tube B contains an iron nail, water that has been boiled, and a layer of oil on top; Tube C contains an iron nail and anhydrous calcium chloride (no water). All tubes are sealed and left for one week. (a) State and explain what would be observed in each tube. (b) State the conclusion of the experiment. (c) Write a word equation for rusting. (6 marks)
Step-by-step solution
1. Step 1
  Tube A (1 A). Iron nail + tap water + air (oxygen present in water and in air gap at top). Nail RUSTS — orange-brown flaky coating of hydrated iron(III) oxide forms. Both required conditions (water + O₂) are present.
2. Step 2
  Tube B (1 A). Boiled water removes dissolved O₂; oil layer prevents air contact. So WATER is present but NO OXYGEN. Nail does NOT rust. This shows oxygen is essential.
3. Step 3
  Tube C (1 A). Anhydrous CaCl₂ absorbs water vapour from the air. So OXYGEN is present (sealed tube has air) but NO WATER. Nail does NOT rust. This shows water is essential.
4. Step 4
  Conclusion (1 B). BOTH oxygen AND water are required for iron to rust. If EITHER is removed, rusting does not occur.
5. Step 5
  Word equation (1 A). iron + oxygen + water → hydrated iron(III) oxide (rust).
  $4\text{Fe} + 3\text{O}_2 + x\text{H}_2\text{O} \rightarrow 2\text{Fe}_2\text{O}_3 \cdot x\text{H}_2\text{O (rust)}$
6. Step 6
  Notes on the variables (1 B). Control variables: same type and size of iron nail; same temperature; same time (one week); sealed tubes (prevent gas exchange). Independent variables: presence/absence of water and oxygen. Dependent variable: whether rust forms (and how much).
Answer
Tube A: rusts (water + O₂ both present). Tube B: no rust (water but no O₂ — boiled water removes O₂; oil prevents re-entry). Tube C: no rust (O₂ but no water — CaCl₂ absorbs water vapour). Conclusion: BOTH water AND O₂ are needed for rusting. Equation: iron + oxygen + water → hydrated iron(III) oxide.
Examiner tip
Edexcel 6-mark mark scheme: 3 marks for correct observations in each tube; 1 for conclusion (both needed); 1 for word equation; 1 for at least one control variable. Common error: not explaining HOW the oil/CaCl₂ excludes the relevant condition.
3Order metals using reactions with acid and water (5 marks, Paper 1)
Core• Adapted from 4CH1/1CR May/Jun 2024 Q5• reactivity series, ordering, spec-2.14, spec-2.15
Question
Four metals W, X, Y, Z were tested with cold water and with dilute hydrochloric acid. The observations are summarised below. Place W, X, Y, Z in DECREASING order of reactivity and justify your order. (5 marks)

Metal Cold water Dilute HCl
W No reaction Slow fizz
X Vigorous fizz, dissolves Explosive (dangerous)
Y No reaction No reaction
Z No reaction Vigorous fizz
Step-by-step solution
1. Step 1
  Analyse cold water reactions (1 M). Only X reacts with cold water (vigorous fizz) — X must be a VERY REACTIVE metal (e.g. Na, Ca). W, Y, Z do not react with cold water → less reactive than X.
2. Step 2
  Analyse dilute HCl reactions (1 M). X reacts explosively → most reactive. Z reacts vigorously → very reactive but less than X. W reacts slowly → less reactive than Z. Y doesn't react with acid → less reactive than H (below H in the series).
3. Step 3
  Build the order (1 A). Decreasing reactivity: X > Z > W > Y.
4. Step 4
  Justification using both tests (1 B). X reacts with both cold water (vigorous) AND HCl (explosive) → must be most reactive (similar to Na or Ca). Z and W react with HCl but not cold water → moderate reactivity (similar to Mg/Zn/Fe range). Z fizzes more vigorously than W → Z > W. Y reacts with neither → below hydrogen (similar to Cu).
5. Step 5
  Comparison with the standard series (1 B). Mapping: X could be Na (reacts with cold water); Z could be Mg (vigorous fizz with HCl, slow with cold water); W could be Fe (slow fizz with HCl); Y could be Cu (no reaction with dilute acid). Standard series gives Na > Mg > Fe > Cu — consistent with X > Z > W > Y.
Answer
Order: X > Z > W > Y (decreasing reactivity). Justification: X is the only one reacting with cold water → most reactive. Among the others: Z fizzes vigorously with HCl (most reactive of these); W only slowly (next); Y not at all (least). Matches standard series Na > Mg > Fe > Cu.
Examiner tip
Edexcel 5-mark mark scheme: 1 for correct order; 1 for using cold-water test to place X at the top; 1 for using HCl test to distinguish Z from W; 1 for placing Y at the bottom; 1 for clear justification logic. ECF applies if the order is wrong but reasoning is sound. Always justify using the EVIDENCE in the table, not by guessing identities.
4Define oxidation and reduction in two ways (4 marks, Paper 1)
Core• Adapted from 4CH1/1C May/Jun 2024 Q6• redox, oxidation, reduction, OIL RIG, spec-2.17, spec-2.18
Question
Consider the reaction: Mg(s) + CuO(s) → MgO(s) + Cu(s). (a) Define oxidation and reduction in terms of OXYGEN. (b) Define oxidation and reduction in terms of ELECTRONS. (c) Identify which species is oxidised and which is reduced. (d) State the name given to a species that brings about reduction. (4 marks)
Step-by-step solution
1. Step 1
  Definitions in terms of oxygen (1 A). Oxidation = GAIN of oxygen. Reduction = LOSS of oxygen. (Historical definition — comes from observations of metal oxides.)
2. Step 2
  Definitions in terms of electrons (1 A). Oxidation = LOSS of electrons. Reduction = GAIN of electrons. Mnemonic: OIL RIG — Oxidation Is Loss, Reduction Is Gain.
3. Step 3
  Identify oxidised/reduced species (1 A). Mg(s) → MgO(s): Mg GAINS oxygen → Mg is OXIDISED. In electron terms: Mg → Mg²⁺ + 2e⁻ (loses electrons → oxidised). CuO(s) → Cu(s): Cu LOSES oxygen → Cu²⁺ is REDUCED. Cu²⁺ + 2e⁻ → Cu (gains electrons → reduced).
4. Step 4
  Reducing agent / oxidising agent (1 B). A species that brings about REDUCTION is called a REDUCING AGENT (or reductant). It is itself OXIDISED in the process. Here: Mg is the reducing agent (it reduces Cu²⁺ to Cu while being oxidised to Mg²⁺). Conversely, CuO is the OXIDISING AGENT (oxidises Mg while being reduced).
Answer
(a) Oxidation = gain of O; Reduction = loss of O. (b) Oxidation = loss of e⁻; Reduction = gain of e⁻ (OIL RIG). (c) Mg is oxidised (gains O / loses e⁻); CuO (Cu²⁺) is reduced (loses O / gains e⁻). (d) A species that causes reduction is a REDUCING AGENT (here, Mg).
Examiner tip
Edexcel 4-mark mark scheme: 1 each for the oxygen and electron definitions; 1 for correct oxidised/reduced identification; 1 for 'reducing agent'. AVOID confusion: a reducing agent is the one being oxidised (it loses electrons and gives them to the other species, reducing it). Test: 'OIL RIG' applies to the species ITSELF, not the agent.
5Explain sacrificial protection of iron (4 marks, Paper 1)
Core• Adapted from 4CH1/1C Jan 2024 Q8• sacrificial protection, rust prevention, galvanising, spec-2.21
Question
Zinc blocks are bolted to the steel hulls of ocean-going ships. (a) Explain how this prevents the iron in the steel from rusting. (b) Explain why galvanising (coating the steel in zinc) protects the iron even if the coating is scratched. (4 marks)
Step-by-step solution
1. Step 1
  Sacrificial protection — basis (1 M). Zinc is MORE REACTIVE than iron in the reactivity series (Zn > Fe). When both are connected and in contact with seawater (an electrolyte), zinc preferentially loses electrons.
2. Step 2
  Zn oxidises in place of Fe (1 A). Zn(s) → Zn²⁺(aq) + 2e⁻. The zinc 'sacrifices' itself — it CORRODES instead of the iron. Electrons released by Zn flow into the iron, keeping the iron at low electrical potential so iron atoms cannot easily lose electrons.
3. Step 3
  Galvanising — barrier method (1 A). Coating steel with zinc is the standard 'galvanising' process (dip in molten zinc, or electroplate). In normal conditions, the zinc forms a tough barrier preventing both water and oxygen from reaching the iron beneath — like paint.
4. Step 4
  Why scratching doesn't matter (1 B). Even if the zinc coating is scratched and the iron is exposed to air and water, the surrounding zinc still works as a SACRIFICIAL anode: Zn is more reactive than Fe, so it preferentially corrodes (Zn → Zn²⁺ + 2e⁻). The iron is protected because the zinc takes the corrosion. This DUAL ROLE (barrier + sacrificial) makes galvanising superior to ordinary paint.
Answer
(a) Zinc is MORE REACTIVE than iron. Zn oxidises preferentially: Zn → Zn²⁺ + 2e⁻. The iron does not lose electrons because the zinc 'sacrifices' itself. (b) Galvanising = (i) barrier method — zinc coats and prevents water + O₂ reaching iron; AND (ii) sacrificial — if scratched, the exposed iron is still protected because the adjacent zinc oxidises preferentially.
Examiner tip
Edexcel 4-mark mark scheme: 1 for Zn more reactive than Fe; 1 for Zn oxidises preferentially / 'sacrifices itself'; 1 for galvanising as a barrier; 1 for sacrificial role still works after scratching. Common error: stating that sacrificial protection requires the Zn to be 'painted on' — actually it just needs electrical contact and a shared electrolyte (sea water).

Metal	Cold water	Dilute HCl
W	No reaction	Slow fizz
X	Vigorous fizz, dissolves	Explosive (dangerous)
Y	No reaction	No reaction
Z	No reaction	Vigorous fizz

Model Answers — Reactivity Series

High-scoring sample answers for reactivity series on the Pearson Edexcel IGCSE 4CH1 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.

Question

4CH1/1C-style — full reactivity series6 marks

Write out the reactivity series of metals (Pearson Edexcel 4CH1 version, including non-metals C and H as reference points). For EACH metal, briefly state what happens with cold water and with dilute hydrochloric acid. (6 marks)

Model answer

Full reactivity series (most reactive at the top).

K > Na > Ca > Mg > Al > (C) > Zn > Fe > (H) > Cu > Ag > Au

(Brackets indicate non-metals included as references for extraction methods.)

Mnemonic: "Please Stop Calling Me A Careless Zebra Instead Try Learning How Copper Saves Gold" — Potassium, Sodium, Calcium, Magnesium, Aluminium, Carbon, Zinc, Iron, Tin, Lead, Hydrogen, Copper, Silver, Gold.

Reactions with cold water and dilute HCl.

Metal	Cold water	Dilute HCl
K (potassium)	Reacts VIOLENTLY — fizzes very vigorously, hydrogen ignites with a lilac flame, may explode	Reacts explosively — dangerous; not normally tested
Na (sodium)	Reacts vigorously — fizzes, melts into a ball, moves on surface, may pop	Reacts violently — dangerous; not normally tested
Ca (calcium)	Reacts steadily — fizzes, white cloudy suspension of Ca(OH)₂ forms	Reacts vigorously — strong fizzing
Mg (magnesium)	Reacts VERY slowly with cold water (barely any reaction); reacts MUCH faster with STEAM: Mg + H₂O → MgO + H₂	Reacts vigorously — strong fizzing, hydrogen evolved
Al (aluminium)	No visible reaction in cold water (protected by thin oxide layer Al₂O₃)	Reacts slowly once oxide layer is removed; vigorous afterwards
(C) (carbon)	—	—
Zn (zinc)	No reaction	Reacts steadily — fizzes; produces H₂
Fe (iron)	No reaction (rusts SLOWLY in moist air — different process)	Reacts slowly — fizzes weakly; produces H₂
(H) (hydrogen)	—	—
Cu (copper)	No reaction	NO reaction (Cu is below H — cannot displace H from acid)
Ag (silver)	No reaction	No reaction
Au (gold)	No reaction	No reaction (gold is so unreactive it is found NATIVE in nature)

Key general patterns.

With cold water: only K, Na, Ca react visibly. Mg reacts very slowly (faster with steam). Everything below Mg gives no visible reaction at room temperature.
With dilute acid: metals ABOVE hydrogen displace H₂ (M + 2HCl → MCl₂ + H₂); metals BELOW hydrogen (Cu, Ag, Au) do NOT react with dilute HCl. So the dilute-acid test divides the series at H.
General equation with acid: M(s) + nHCl(aq) → MClₙ(aq) + (n/2)H₂(g), where n = charge of the metal ion. E.g. Mg + 2HCl → MgCl₂ + H₂.
General equation with water/steam: only K, Na, Ca: M + H₂O → MOH (or M(OH)₂) + ½H₂. For Mg with steam: Mg + H₂O → MgO + H₂ (oxide, not hydroxide, because temperature is high).

Why the order is as it is. Reactivity = ease of losing electrons to form the metal ion. K and Na have one outer electron, easily lost. Ca, Mg, Al lose 2 or 3 outer electrons. Going down the series, the outer electrons are harder to remove because they are closer to the nucleus (or more strongly bound). Cu, Ag, Au resist losing electrons — they tend to stay as the metal.

Why this scores

Edexcel 6-mark mark scheme: 2 for correct order including C and H; 2 for cold-water reactions (any 3-4 metals); 2 for dilute-acid reactions (any 3-4 metals). Position of H and C is critical — they determine extraction methods. Acidified mnemonics earn no marks unless the order is also correct.

Question
4CH1/1C-style — predicting displacement6 marks
Using the reactivity series, predict whether a reaction would occur in EACH of the following experiments. Justify each prediction and write a balanced equation where reaction occurs. (6 marks)

(i) Zn added to MgSO₄(aq) (ii) Mg added to ZnSO₄(aq) (iii) Cu added to AgNO₃(aq) (iv) Fe added to dilute HCl
Model answer
General rule for displacement. A more reactive metal displaces a less reactive metal from a solution of its salt. The displaced metal loses (or fails to lose) electrons depending on its position in the reactivity series.

Reactivity series order (relevant section): Mg > Zn > Fe > (H) > Cu > Ag.

(i) Zn(s) + MgSO₄(aq) — NO REACTION.

Zinc is LESS reactive than magnesium (Zn is below Mg in the series). Zn cannot give electrons to Mg²⁺ because Mg²⁺ already holds its valence electrons more 'eagerly' than Zn would lose them. So no displacement and no reaction. The zinc piece would just sit in the colourless MgSO₄(aq).

(ii) Mg(s) + ZnSO₄(aq) — REACTION OCCURS.

Magnesium is MORE reactive than zinc (Mg is above Zn). Mg loses 2 electrons easily; Zn²⁺ accepts them. So Mg DISPLACES Zn from ZnSO₄.

$\text{Mg(s)} + \text{ZnSO}_4\text{(aq)} \rightarrow \text{MgSO}_4\text{(aq)} + \text{Zn(s)}$

Ionic: Mg + Zn²⁺ → Mg²⁺ + Zn (SO₄²⁻ is the spectator).

Observations: zinc metal deposits (grey/silvery solid); magnesium dissolves. ZnSO₄ and MgSO₄ are both colourless so no obvious solution-colour change.

(iii) Cu(s) + 2AgNO₃(aq) — REACTION OCCURS.

Copper is MORE reactive than silver (Cu is above Ag). Cu loses 2 electrons, transferred to 2 Ag⁺ ions. Cu displaces Ag from AgNO₃ solution.

$\text{Cu(s)} + 2\text{AgNO}_3\text{(aq)} \rightarrow \text{Cu(NO}_3\text{)}_2\text{(aq)} + 2\text{Ag(s)}$

Ionic: Cu + 2Ag⁺ → Cu²⁺ + 2Ag.

Observations: colourless silver nitrate turns blue (Cu²⁺ ions); silver crystals form on the copper wire (visible as a 'silver tree' if a wire is suspended in the solution). The copper wire becomes thinner.

(iv) Fe(s) + 2HCl(aq) — REACTION OCCURS.

Iron is ABOVE hydrogen in the reactivity series. Fe can displace hydrogen from the acid:

$\text{Fe(s)} + 2\text{HCl(aq)} \rightarrow \text{FeCl}_2\text{(aq)} + \text{H}_2\text{(g)}$

Ionic: Fe + 2H⁺ → Fe²⁺ + H₂.

Observations: pale green FeCl₂ solution forms; bubbles of H₂ gas; iron dissolves slowly (Fe is only just above H — reaction is gentle). H₂ pops with a lighted splint.

Summary table.

Reaction Outcome Reason
Zn + MgSO₄ No reaction Zn < Mg in series
Mg + ZnSO₄ Reaction Mg > Zn in series
Cu + AgNO₃ Reaction Cu > Ag in series
Fe + HCl Reaction Fe > H in series
Why this scores
Edexcel 6-mark mark scheme: 1 mark each for the correct prediction (yes/no) on all four parts; plus 1 mark each for the balanced equations in the three cases where reaction occurs (max 6). Common error: NOT balancing the silver equation (1 Cu : 2 Ag⁺) because Cu loses 2 e⁻ but each Ag⁺ accepts only 1 e⁻.
Question
4CH1/2C-style — redox detailed analysis5 marks
For the reaction: 2Mg(s) + O₂(g) → 2MgO(s), explain in detail what is oxidised and what is reduced, using BOTH the oxygen-based definition AND the electron-transfer definition. Identify the oxidising agent and the reducing agent. (5 marks)
Model answer
The reaction. Magnesium burns brilliantly in oxygen with a bright white light to form a white solid:

$2\text{Mg(s)} + \text{O}_2\text{(g)} \rightarrow 2\text{MgO(s)}$

MgO is an ionic solid: Mg²⁺O²⁻ in a giant ionic lattice.

Analysis in terms of OXYGEN (the historical definition).

Mg is OXIDISED: it GAINS oxygen — going from elemental Mg(s) to combined Mg in MgO.

O₂ is REDUCED: oxygen LOSES its 'separate' identity — going from O₂ (uncombined element) to O²⁻ in MgO. (In Edexcel's loose 'oxygen' definition, the gas oxygen becomes 'oxide' in a compound — counted as 'losing oxygen' from the perspective of going from O₂ to combined O.)

Analysis in terms of ELECTRONS (the modern definition).

This is the more useful definition for ionic / redox reactions.

Mg is OXIDISED: each Mg atom LOSES 2 electrons to form Mg²⁺. Oxidation Is Loss (OIL).

$\text{Mg} \rightarrow \text{Mg}^{2+} + 2e^-$

O₂ is REDUCED: each O atom GAINS 2 electrons to form O²⁻. Reduction Is Gain (RIG).

$\text{O}_2 + 4e^- \rightarrow 2\text{O}^{2-}$

(Note: for one O₂ molecule, 4 electrons are needed — supplied by 2 Mg atoms losing 2 e⁻ each.)

The full electron-transfer picture. 4 electrons are transferred from 2 Mg atoms to 1 O₂ molecule. This forms 2 Mg²⁺ ions and 2 O²⁻ ions, which assemble into 2 'MgO' formula units in the ionic lattice.

Oxidising agent vs reducing agent.

The oxidising agent is the species that CAUSES oxidation of something else — i.e. it accepts the electrons. Here, O₂ is the oxidising agent (it removes electrons from Mg; it is itself reduced).

The reducing agent is the species that CAUSES reduction of something else — i.e. it donates the electrons. Here, Mg is the reducing agent (it gives electrons to O₂; it is itself oxidised).

Mnemonic check. 'The oxidising agent OXIDISES; in doing so, it is itself REDUCED.' So O₂ (oxidising agent) gets reduced to O²⁻. ✓ Same for Mg (reducing agent) is oxidised to Mg²⁺.

General principle. This applies to ALL redox reactions:

In displacement: Fe + Cu²⁺ → Fe²⁺ + Cu. Fe is the reducing agent (gives e⁻ → oxidised to Fe²⁺). Cu²⁺ is the oxidising agent (takes e⁻ → reduced to Cu).

In combustion of metals with oxygen.

In thermal reduction of metal oxides with carbon (e.g. CuO + C → Cu + CO).

In electrolysis (cathode = reduction; anode = oxidation).
Why this scores
Edexcel 5-mark mark scheme: 1 for stating Mg is oxidised (oxygen gain / e⁻ loss); 1 for stating O₂ is reduced (e⁻ gain); 1 for correct half-equation Mg → Mg²⁺ + 2e⁻ (or O₂ + 4e⁻ → 2O²⁻); 1 for identifying the oxidising agent (O₂); 1 for identifying the reducing agent (Mg). Mark scheme accepts both definitions but rewards the e⁻ explanation more heavily.

Reaction	Outcome	Reason
Zn + MgSO₄	No reaction	Zn < Mg in series
Mg + ZnSO₄	Reaction	Mg > Zn in series
Cu + AgNO₃	Reaction	Cu > Ag in series
Fe + HCl	Reaction	Fe > H in series

Question

4CH1/2C-style — rust prevention methods6 marks

Compare FOUR methods used to prevent the rusting of iron objects. For EACH method, state what it does, how it works, give ONE example application, and identify ONE limitation. (6 marks)

Model answer

Iron rusts in the combined presence of water and oxygen. All methods of rust prevention work by either (i) blocking access of water/O₂ to the iron, or (ii) providing a more reactive metal that corrodes instead, or (iii) coating with a less reactive metal.

Method 1 — Painting / oil / grease (barrier method).

What it does. Provides a physical layer between the iron and the surrounding air and moisture.
How it works. Paint/oil/grease coats the surface, preventing water and oxygen from contacting the iron atoms — without contact, the rusting reaction cannot start.
Example. Cars, bicycles, garden gates, oil/grease on tools and machinery, polyurethane varnish on iron railings.
Limitation. If the coating is SCRATCHED, the exposed iron rusts in that spot — and rust can spread UNDER the paint film, eventually causing it to flake off.

Method 2 — Galvanising (zinc coating).

What it does. Coats the iron / steel with a thin layer of zinc, usually by dipping in molten zinc ('hot-dip galvanising').
How it works. Operates by TWO mechanisms: (1) BARRIER — the zinc coat prevents air and water from reaching the iron; (2) SACRIFICIAL — if the coating is scratched and iron is exposed, the zinc (more reactive than iron) still preferentially oxidises (Zn → Zn²⁺ + 2e⁻), protecting the iron.
Example. Galvanised steel nails, roof sheets, chain-link fencing, dustbins, motorway crash barriers.
Limitation. Eventually the zinc is consumed by sacrificial corrosion and the protection runs out; visual appearance (matte grey) less attractive than paint; more expensive than ordinary paint.

Method 3 — Sacrificial protection (zinc or magnesium blocks).

What it does. A piece of a MORE reactive metal (typically zinc or magnesium) is bolted or attached to the iron object in electrical contact.
How it works. Because the attached metal is MORE reactive, it preferentially loses electrons (Zn → Zn²⁺ + 2e⁻ or Mg → Mg²⁺ + 2e⁻), corroding away while the iron is preserved. The electrons supplied to the iron keep its electrical potential too low for it to lose electrons itself.
Example. Zinc blocks bolted to ship hulls (replaced every few years); magnesium 'anodes' attached to buried iron oil pipelines or domestic boiler hot-water tanks.
Limitation. The sacrificial metal must be replaced regularly as it corrodes; needs electrical contact with the iron; only works where there is an electrolyte (seawater, moist soil) to complete the electrochemical cell.

Method 4 — Tin plating ('tin cans') / chromium plating (less reactive metal barrier).

What it does. Coats the iron with a layer of a LESS reactive metal — tin, chromium, or nickel — usually by electroplating.
How it works. Pure barrier method. The unreactive coating doesn't itself corrode and shields the iron from air/water.
Example. 'Tin' cans for food (tin-plated steel — tin is non-toxic and unreactive); chrome-plated steel taps, car bumpers; nickel-plated kitchen utensils.
Limitation. If scratched, the situation is now WORSE than for galvanising: because the coating metal is LESS reactive than iron, the iron will preferentially corrode at the scratch — and the coating actually ACCELERATES rusting at the exposed spot ('cathodic protection in reverse'). Must keep the coating intact.

Summary table.

Method	Mechanism	Example	Limitation
Paint / oil	Barrier	Cars, railings	Fails if scratched
Galvanising	Barrier + sacrificial	Roof sheets	Zinc eventually consumed
Sacrificial Zn/Mg blocks	Sacrificial only	Ship hulls, pipelines	Blocks must be replaced
Tin / Cr plating	Barrier only	Food cans, taps	Accelerates rust if scratched

Why this scores

Edexcel 6-mark mark scheme: 1 mark for stating each of FOUR methods + how it works (mechanism); 1 mark for an example or limitation across the four methods (1 per method, max 2). Stretch yourself for marks 5-6 by including BOTH barrier and sacrificial roles of galvanising. Common error: confusing sacrificial protection (separate block, transferable) with galvanising (whole-surface coating).

Key Definitions and Keywords — Reactivity Series

Definitions to memorise and the exact keywords mark schemes credit for reactivity series answers — sharpened from recent examiner reports for the 2026 Pearson Edexcel IGCSE 4CH1 sitting.

Reactivity series
Examiner keyword
An ordered list of metals from most to least reactive (most willing to lose electrons / form positive ions). Standard 4CH1 order: K > Na > Ca > Mg > Al > (C) > Zn > Fe > (H) > Cu > Ag > Au. Carbon and hydrogen are included as reference points for extraction methods.
Displacement reaction
Examiner keyword
A redox reaction in which a more reactive metal takes the place of a less reactive metal in a compound or solution. Example: Fe + CuSO₄ → FeSO₄ + Cu (Fe more reactive than Cu, so Fe displaces Cu).
Oxidation (oxygen definition)
Examiner keyword
Gain of oxygen by a species. Example: Mg + O → MgO; Mg is oxidised (gains O).
Reduction (oxygen definition)
Examiner keyword
Loss of oxygen from a species. Example: CuO + H₂ → Cu + H₂O; Cu²⁺ is reduced (CuO loses oxygen).
Oxidation (electron definition)
Examiner keyword
Loss of electrons by a species. Example: Fe → Fe²⁺ + 2e⁻ (Fe is oxidised). Mnemonic: OIL — Oxidation Is Loss (of electrons).
Reduction (electron definition)
Examiner keyword
Gain of electrons by a species. Example: Cu²⁺ + 2e⁻ → Cu (Cu²⁺ is reduced to Cu). Mnemonic: RIG — Reduction Is Gain (of electrons).
Oxidising agent
Examiner keyword
A species that brings about oxidation of another — it accepts electrons and is itself reduced. Examples: O₂, Cl₂, Cu²⁺ (in displacement reactions).
Reducing agent
Examiner keyword
A species that brings about reduction of another — it donates electrons and is itself oxidised. Examples: more-reactive metals (Mg, Zn, Fe in displacement); carbon (in metal extraction); hydrogen.
Rusting
Examiner keyword
The corrosion of iron in the presence of BOTH water AND oxygen, producing hydrated iron(III) oxide (Fe₂O₃·xH₂O) — the orange-brown 'rust'. Equation: 4Fe + 3O₂ + xH₂O → 2Fe₂O₃·xH₂O.
Sacrificial protection
Examiner keyword
Preventing rusting by attaching a more reactive metal (Zn or Mg) to the iron object. The reactive metal corrodes preferentially, protecting the iron. Used on ship hulls, oil pipelines, water tanks.
Galvanising
Examiner keyword
Coating iron or steel with a layer of zinc (often by hot-dipping). Provides both a BARRIER (preventing air/water from reaching iron) AND SACRIFICIAL protection (if scratched, the Zn still corrodes preferentially).

Common Mistakes and Misconceptions — Reactivity Series

The traps other students keep falling into on reactivity series questions — taken from recent Pearson Edexcel IGCSE 4CH1 examiner reports and mark schemes — and how to avoid them.

✕Predicting that a LESS reactive metal can displace a MORE reactive one (e.g. Cu can displace Zn)
4CH1 Examiner Reports 2022-2024
Why it happens
Not understanding which way the electron flow needs to go.
How to avoid it
The MORE reactive metal loses electrons more easily, so it does the displacing. Order: in 'Zn + CuSO₄', Zn is MORE reactive → Zn displaces Cu (yes reaction). In 'Cu + ZnSO₄', Cu is LESS reactive → no reaction. Check the series: the metal that's HIGHER in the list wins.
✕Mixing up oxidation and reduction with OIL RIG
Why it happens
Remembering OIL RIG but applying it the wrong way.
How to avoid it
OIL = Oxidation Is Loss (of electrons). RIG = Reduction Is Gain (of electrons). The reaction happens TO the species ITSELF — not 'the agent'. Mg → Mg²⁺ + 2e⁻: Mg loses e⁻ → Mg is OXIDISED (= itself oxidised; Mg is the reducing agent).
✕Confusing the roles of the three test tubes in the rusting experiment
4CH1 Examiner Reports 2023-2024
Why it happens
Not understanding what each variable controls.
How to avoid it
Tube A: water + O₂ (positive control — rusts). Tube B: water but NO O₂ (boiled + oil — proves O₂ needed). Tube C: O₂ but NO water (CaCl₂ removes moisture — proves water needed). Outcome: A rusts; B and C don't. Conclusion: BOTH O₂ AND water needed.
✕Saying that galvanising fails as soon as the coating is scratched
4CH1 Examiner Reports 2022-2024
Why it happens
Thinking that a barrier only works if intact.
How to avoid it
Galvanising provides TWO mechanisms: barrier + sacrificial protection. Even if scratched, the surrounding ZINC is more reactive than iron → it oxidises preferentially (Zn → Zn²⁺ + 2e⁻). So the iron stays protected. Contrast with TIN-plating: if scratched, tin is LESS reactive than iron → iron rusts faster.
✕Stating that 'zinc doesn't rust' as the reason for galvanising
Why it happens
Confusing 'doesn't rust' (no reaction with O₂ and H₂O) with 'protects iron' (provides electrons).
How to avoid it
Zinc DOES corrode (forms ZnO and Zn(OH)₂); it just corrodes preferentially because it's more reactive. The point of galvanising is that the zinc's corrosion SHIELDS the iron beneath — not that zinc is itself uncorrodible.
✕Identifying only some redox reactions as 'redox' (e.g. excluding combustion)
Why it happens
Associating redox only with metal-displacement contexts.
How to avoid it
REDOX = ANY reaction involving electron transfer / oxidation state change. Includes: combustion (Mg + O₂ → MgO), displacement (Fe + Cu²⁺ → Fe²⁺ + Cu), thermal reduction (CuO + C → Cu + CO), electrolysis (cathode + anode reactions). All of these are redox.

Practice questions

Exam-style questions with step-by-step worked solutions. Try one before checking the method.

Past paper style quiz

Get a report showing which sub-topics you've nailed and which ones still need work.

Video lesson

Short walkthrough of the concepts students most often get stuck on.

Reactivity Series — frequently asked questions

The things students keep getting wrong in this sub-topic, answered.

Reactivity Series — Pearson Edexcel International GCSE Chemistry 4CH1 Study Notes (2026 onwards, Spec Issue 4)

Metal

Observation

Reaction

Reacts VIOLENTLY; ignites with lilac flame

2K + 2H₂O → 2KOH + H₂

Vigorous; melts into ball; moves on surface

2Na + 2H₂O → 2NaOH + H₂

Steady fizz; cloudy Ca(OH)₂ forms

Ca + 2H₂O → Ca(OH)₂ + H₂

Very slow with cold water (faster with STEAM)

Mg + H₂O → MgO + H₂ (steam)

Al, Zn, Fe, Cu, Ag, Au

No visible reaction with cold water

—

Metal

Observation

K, Na, Ca

Reacts EXPLOSIVELY — dangerous; not normally tested

Reacts vigorously — strong fizz; H₂ pops

Reacts slowly (oxide layer needs to be removed first); then vigorously

Reacts steadily — fizz

Reacts slowly — gentle fizz; pale green FeCl₂ solution

Cu, Ag, Au

NO reaction — below H in the series

Metal

Observation

K, Na

Burn vigorously with characteristic flames (red, yellow)

Burns brilliant WHITE light → white MgO

Slow oxidation forms protective Al₂O₃

Zn, Fe

Slowly form oxide with heat

Slowly forms black CuO on heating

Ag, Au

Au does not oxidise; Ag tarnishes very slowly

Reaction

Outcome

Why

Mg + ZnSO₄ → MgSO₄ + Zn

Reaction occurs

Mg > Zn

Zn + MgSO₄

No reaction

Zn < Mg

Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag

Reaction occurs

Cu > Ag — silvery deposit on Cu wire

Ag + CuSO₄

No reaction

Ag < Cu

Mg + 2HCl → MgCl₂ + H₂

Reaction occurs

Mg > H (displaces H)

Cu + HCl

No reaction

Cu < H

Process

Oxygen definition

Electron definition

Oxidation

GAIN of oxygen

LOSS of electrons

Reduction

LOSS of oxygen

GAIN of electrons

Tube

Contents

Outcome

Why

Iron nail + tap water + air

RUSTS

Both water and O₂ present

Iron nail + boiled water + oil layer on top

NO rust

Water but NO O₂ (boiled out + sealed by oil)

Iron nail + anhydrous CaCl₂ (dries the air)

NO rust

O₂ but NO water

Method

Barrier?

Sacrificial?

Best for

Paint / oil

Yes

Cars, large structures

Galvanising

Yes

Yes (if scratched)

Roofs, fencing, nails

Sacrificial blocks

Yes

Ships, pipelines, tanks

Tin / Cr plating

Yes

No (worse if scratched)

Food cans, decorative

Metal	Cold water	Dilute HCl
W	No reaction	Slow fizz
X	Vigorous fizz, dissolves	Explosive (dangerous)
Y	No reaction	No reaction
Z	No reaction	Vigorous fizz

Metal

Cold water

Dilute HCl

No reaction

Slow fizz

Vigorous fizz, dissolves

Explosive (dangerous)

No reaction

Vigorous fizz

Metal

Cold water

Dilute HCl

K (potassium)

Reacts VIOLENTLY — fizzes very vigorously, hydrogen ignites with a lilac flame, may explode

Reacts explosively — dangerous; not normally tested

Na (sodium)

Reacts vigorously — fizzes, melts into a ball, moves on surface, may pop

Reacts violently — dangerous; not normally tested

Ca (calcium)

Reacts steadily — fizzes, white cloudy suspension of Ca(OH)₂ forms

Reacts vigorously — strong fizzing

Mg (magnesium)

Reacts VERY slowly with cold water (barely any reaction); reacts MUCH faster with STEAM: Mg + H₂O → MgO + H₂

Reacts vigorously — strong fizzing, hydrogen evolved

Al (aluminium)

No visible reaction in cold water (protected by thin oxide layer Al₂O₃)

Reacts slowly once oxide layer is removed; vigorous afterwards

(C) (carbon)

—

Zn (zinc)

No reaction

Reacts steadily — fizzes; produces H₂

Fe (iron)

No reaction (rusts SLOWLY in moist air — different process)

Reacts slowly — fizzes weakly; produces H₂

(H) (hydrogen)

—

Cu (copper)

No reaction

NO reaction (Cu is below H — cannot displace H from acid)

Ag (silver)

No reaction

Au (gold)

No reaction

No reaction (gold is so unreactive it is found NATIVE in nature)

Reaction	Outcome	Reason
Zn + MgSO₄	No reaction	Zn < Mg in series
Mg + ZnSO₄	Reaction	Mg > Zn in series
Cu + AgNO₃	Reaction	Cu > Ag in series
Fe + HCl	Reaction	Fe > H in series

Reaction

Outcome

Reason

Zn + MgSO₄

No reaction

Zn < Mg in series

Mg + ZnSO₄

Reaction

Mg > Zn in series

Cu + AgNO₃

Reaction

Cu > Ag in series

Fe + HCl

Reaction

Fe > H in series

The reaction. Magnesium burns brilliantly in oxygen with a bright white light to form a white solid:

$2\text{Mg(s)} + \text{O}_2\text{(g)} \rightarrow 2\text{MgO(s)}$

MgO is an ionic solid: Mg²⁺O²⁻ in a giant ionic lattice.

Analysis in terms of OXYGEN (the historical definition).

Mg is OXIDISED: it GAINS oxygen — going from elemental Mg(s) to combined Mg in MgO.
O₂ is REDUCED: oxygen LOSES its 'separate' identity — going from O₂ (uncombined element) to O²⁻ in MgO. (In Edexcel's loose 'oxygen' definition, the gas oxygen becomes 'oxide' in a compound — counted as 'losing oxygen' from the perspective of going from O₂ to combined O.)

Analysis in terms of ELECTRONS (the modern definition).

This is the more useful definition for ionic / redox reactions.

Mg is OXIDISED: each Mg atom LOSES 2 electrons to form Mg²⁺. Oxidation Is Loss (OIL).

$\text{Mg} \rightarrow \text{Mg}^{2+} + 2e^-$

O₂ is REDUCED: each O atom GAINS 2 electrons to form O²⁻. Reduction Is Gain (RIG).

$\text{O}_2 + 4e^- \rightarrow 2\text{O}^{2-}$

(Note: for one O₂ molecule, 4 electrons are needed — supplied by 2 Mg atoms losing 2 e⁻ each.)

The full electron-transfer picture. 4 electrons are transferred from 2 Mg atoms to 1 O₂ molecule. This forms 2 Mg²⁺ ions and 2 O²⁻ ions, which assemble into 2 'MgO' formula units in the ionic lattice.

Oxidising agent vs reducing agent.

The oxidising agent is the species that CAUSES oxidation of something else — i.e. it accepts the electrons. Here, O₂ is the oxidising agent (it removes electrons from Mg; it is itself reduced).
The reducing agent is the species that CAUSES reduction of something else — i.e. it donates the electrons. Here, Mg is the reducing agent (it gives electrons to O₂; it is itself oxidised).

Mnemonic check. 'The oxidising agent OXIDISES; in doing so, it is itself REDUCED.' So O₂ (oxidising agent) gets reduced to O²⁻. ✓ Same for Mg (reducing agent) is oxidised to Mg²⁺.

General principle. This applies to ALL redox reactions:

In displacement: Fe + Cu²⁺ → Fe²⁺ + Cu. Fe is the reducing agent (gives e⁻ → oxidised to Fe²⁺). Cu²⁺ is the oxidising agent (takes e⁻ → reduced to Cu).
In combustion of metals with oxygen.
In thermal reduction of metal oxides with carbon (e.g. CuO + C → Cu + CO).
In electrolysis (cathode = reduction; anode = oxidation).

Method

Mechanism

Example

Limitation

Paint / oil

Barrier

Cars, railings

Fails if scratched

Galvanising

Barrier + sacrificial

Roof sheets

Zinc eventually consumed

Sacrificial Zn/Mg blocks

Sacrificial only

Ship hulls, pipelines

Blocks must be replaced

Tin / Cr plating

Barrier only

Food cans, taps

Accelerates rust if scratched

Reactivity Series

Short Study Notes in the form of Slides

Detailed Study Notes

What you’ll learn

How it’s examined

1Iron nail in copper(II) sulfate — displacement reaction (5 marks, Paper 1)

2Required practical: investigating rusting of iron (6 marks, Paper 1)

3Order metals using reactions with acid and water (5 marks, Paper 1)

4Define oxidation and reduction in two ways (4 marks, Paper 1)

5Explain sacrificial protection of iron (4 marks, Paper 1)

Reactivity series

Displacement reaction

Oxidation (oxygen definition)

Reduction (oxygen definition)

Oxidation (electron definition)

Reduction (electron definition)

Oxidising agent

Reducing agent

Rusting

Sacrificial protection

Galvanising

✕Predicting that a LESS reactive metal can displace a MORE reactive one (e.g. Cu can displace Zn)

✕Mixing up oxidation and reduction with OIL RIG

✕Confusing the roles of the three test tubes in the rusting experiment

✕Saying that galvanising fails as soon as the coating is scratched

✕Stating that 'zinc doesn't rust' as the reason for galvanising

✕Identifying only some redox reactions as 'redox' (e.g. excluding combustion)

Practice questions

Past paper style quiz

Assess your understanding

Video lesson

Reactivity Series — frequently asked questions

Reactivity Series

Short Study Notes in the form of Slides

Detailed Study Notes

What you’ll learn

How it’s examined

1Iron nail in copper(II) sulfate — displacement reaction (5 marks, Paper 1)

2Required practical: investigating rusting of iron (6 marks, Paper 1)

3Order metals using reactions with acid and water (5 marks, Paper 1)

4Define oxidation and reduction in two ways (4 marks, Paper 1)

5Explain sacrificial protection of iron (4 marks, Paper 1)

Reactivity series

Displacement reaction

Oxidation (oxygen definition)

Reduction (oxygen definition)

Oxidation (electron definition)

Reduction (electron definition)

Oxidising agent

Reducing agent

Rusting

Sacrificial protection

Galvanising

✕Predicting that a LESS reactive metal can displace a MORE reactive one (e.g. Cu can displace Zn)

✕Mixing up oxidation and reduction with OIL RIG

✕Confusing the roles of the three test tubes in the rusting experiment

✕Saying that galvanising fails as soon as the coating is scratched

✕Stating that 'zinc doesn't rust' as the reason for galvanising

✕Identifying only some redox reactions as 'redox' (e.g. excluding combustion)

Practice questions

Past paper style quiz

Assess your understanding

Video lesson

Reactivity Series — frequently asked questions