2.1Unit 1 · Inorganic Chemistry
Reactivity series — Edexcel IGCSE Chemistry Modular - UNIT 1 Revision Notes & Topical Questions
10 min read 7 parts Lesson 1 of 4 1 quiz
Lesson summary
Describe how metals react with water, steam and dilute acids.Metal + water → metal hydroxide + hydrogen (reactive metals).Metal + steam → metal oxide + hydrogen (e.g.
- Metals with water and acids
- Displacement
- Order of reactivity
- Rusting of iron
- Oxidation and reduction
- Carbon and hydrogen in the series
Section 1 of 7Reactivity series
Essential knowledge
Metals with water and acids
Metals with water and acids potassium, sodium, lithium and calcium react with cold water to form a hydroxide and hydrogen, e.g. 2Na + 2H2O → 2NaOH + H2. Magnesium, zinc and iron react with steam to form an oxide and hydrogen. Copper does not react with water.
With dilute acids, metals above hydrogen form a salt and hydrogen, e.g. Zn + H2SO4 → ZnSO4 + H2. The more reactive the metal, the faster the bubbling and the bigger the temperature rise. Copper, silver and gold do not react.
Displacement
Displacement a more reactive metal displaces a less reactive metal from a solution of its salt, e.g. Mg + CuSO4 → MgSO4 + Cu. No reaction occurs if the added metal is less reactive. Displacement also occurs with oxides (thermite: Al + Fe2O3).
Order of reactivity
K, Na, Li, Ca, Mg, Al, Zn, Fe, Cu, Ag, Au. Reactivity depends on how easily a metal atom loses its outer electrons to form a positive ion.
Rusting of iron
Rusting of iron iron rusts only when both water and oxygen (air) are present, forming hydrated iron(III) oxide. A test-tube experiment with boiled water plus oil (no air) and calcium chloride (no water) shows both are needed.
Rusting is prevented by barrier methods (paint, oil, grease, plastic) and by galvanising or sacrificial protection with zinc or magnesium, which are more reactive than iron and are oxidised in its place.
Oxidation and reduction
Oxidation and reduction oxidation is gain of oxygen or loss of electrons; reduction is loss of oxygen or gain of electrons. In a displacement reaction the more reactive metal is oxidised and the metal ion is reduced.
Practical
Practical to compare metals fairly, use the same mass and surface area of metal, same acid volume and concentration, and same starting temperature; judge by rate of gas production or temperature rise.
Carbon and hydrogen in the series
Carbon is placed between aluminium and zinc: metals below carbon can be extracted by heating their oxides with carbon. Hydrogen is placed between iron and copper in the simplified series: metals above it give hydrogen with dilute acids.
Calcium and water
Calcium reacts steadily with cold water to form calcium hydroxide and hydrogen: Ca + 2H2O → Ca(OH)2 + H2. The solution becomes cloudy because calcium hydroxide is only slightly soluble.
Displacement from metal oxides
Heating a metal with the oxide of a less reactive metal causes displacement, e.g. Mg + CuO → MgO + Cu. Magnesium removes oxygen, so it is the reducing agent; copper(II) oxide gives up oxygen, so it is the oxidising agent. No reaction occurs if the metal is less reactive.
Spectator ions and half equations
Ions that are unchanged in a reaction are spectator ions and are left out of the ionic equation. For magnesium in silver nitrate: Mg + 2Ag+ → Mg2+ + 2Ag. Half equations: Mg → Mg2+ + 2e− (oxidation) and Ag+ + e− → Ag (reduction).
Spotting oxidation from charges
If an ion's charge becomes more positive it has lost electrons, so it is oxidised, e.g. Fe2+ → Fe3+. If the charge becomes less positive it has gained electrons and is reduced, e.g. Cu2+ → Cu.
Why scratched iron keeps rusting
Barrier coatings only work while unbroken. Rust is porous and flakes off, so once a coating is scratched, water and oxygen keep reaching fresh iron underneath and the structure is gradually weakened.
Replacing sacrificial metal
Zinc or magnesium blocks on ships and pipelines are oxidised instead of the iron, so they are slowly used up. They must be replaced before they corrode away completely, or the iron will start to rust.
Corrosion vs rusting
Corrosion is the general term for a metal being worn away by reaction with substances in its surroundings. Rusting is the particular corrosion of iron and steel, which needs both water and oxygen.
Test for hydrogen
A lighted splint held at the mouth of a test tube of hydrogen gives a squeaky pop. This confirms the gas made when a metal reacts with a dilute acid.
Section 2 of 7Process & sequence
1
Place equal-sized pieces of different metals in separate test tubes.
2
Add the same volume and concentration of dilute hydrochloric acid to each.
3
Keep the temperature the same and start timing.
4
Observe the rate of bubbling or measure the temperature rise.
5
Rank the metals from most to least vigorous reaction.
6
Confirm the order using displacement reactions with metal salt solutions.
Magnesium displacing copperwrite these steps in this order; each step is a marking point.
1
Mg added to CuSO4(aq)
2
Mg atoms lose 2 electrons
3
Cu2+ ions gain 2 electrons
4
Copper metal deposits
5
Solution turns colourless
Section 3 of 7Compare
| Metal | With cold water | With dilute HCl |
|---|---|---|
| Potassium | Very vigorous, H2 ignites | Explosive (not done) |
| Sodium | Vigorous, melts, fizzes | Explosive (not done) |
| Calcium | Steady fizzing | Vigorous |
| Magnesium | Very slow (reacts with steam) | Rapid fizzing |
| Zinc / Iron | No reaction (react with steam) | Moderate / slow fizzing |
| Copper | No reaction | No reaction |
OrderK > Na > Li > Ca > Mg > Al > Zn > Fe > Cu > Ag > Au (with carbon and hydrogen placed as reference points).
| Method | How it works |
|---|---|
| Paint, oil or grease | Barrier keeps out water and oxygen |
| Plastic coating | Barrier keeps out water and oxygen |
| Galvanising (zinc coating) | Barrier, plus zinc corrodes in preference if scratched |
| Sacrificial blocks of Mg or Zn | More reactive metal is oxidised instead of iron |
Section 4 of 7Worked examples
Oxidised
Iron is added to copper(II) sulfate solution. Describe what you would see and identify the species oxidised and reduced.
- The blue solution fades to pale green and a brown/pink solid (copper) forms on the iron.
- Fe + CuSO4 → FeSO4 + Cu.
- IonicFe + Cu2+ → Fe2+ + Cu.
- Iron loses electrons so it is oxidised; Cu2+ gains electrons so it is reduced.
Between zinc and copper
Metal X displaces copper but not zinc from their salt solutions. Where is X in the reactivity series?
- X is more reactive than copper (it displaces it) but less reactive than zinc (it cannot displace it).
- So X lies between zinc and copper, e.g. iron.
Section 5 of 7Key terms
Section 6 of 7Command terms
Command terms
Give / State / Name
Recall a fact; one idea per mark.
Define
Give the exact meaning using the specification keywords.
Describe
Give an account of what happens / the pattern in data, quoting values; no reasons needed.
Explain
Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.
Suggest
Use knowledge in a new context; more than one answer may be accepted.
Compare
Similarities and differences; each point must refer to both items.
Calculate
Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.
Discuss
Explore the issue from different angles and link the points.
Evaluate / Assess
Weigh strengths and weaknesses and reach a supported judgement.
Deduce
Draw a conclusion from the information given.
Justify
Support a statement/choice with evidence.
Section 7 of 7Exam technique
Keywords the mark scheme looks for in this lesson
Keywords the mark scheme looks for in this lesson
Reactivity series · Displacement reaction · Oxidation · Reduction · Redox · Oxidising agent · Reducing agent · Rusting · Sacrificial protection · Galvanising
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.
How to get full marks (examiner guidance)
How to get full marks (examiner guidance)
Use specification keywords exactly (e.g. electronegativity, nucleophile, dynamic equilibrium, activation energy).
Link ideas
Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.
Use the information in the question
“discuss/evaluate” answers must use the data provided and match the number of marks.
Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.
Avoid vague words
“it”, “stuff”, “things”, “goes up”, “energy is made”. Name the substance and the process.
Do not extrapolate a graph line beyond the data or to zero unless asked.
Six-mark extended responses are marked on content AND a logical, linked line of reasoning.
Marked practiceQuizzes for this lesson
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