Section 1 of 8Extraction of Metals
1
Most metals are found as compounds (oxides, sulfides, carbonates) in ores; very unreactive metals such as gold occur uncombined.
2
Extraction involves reduction. Metals below carbon in the reactivity series are reduced by heating with carbon; metals above carbon need electrolysis, which is expensive because of the large amount of electricity used.
3
In the blast furnace, coke burns in hot air giving CO2 and heat; CO2 reacts with more coke to form carbon monoxide, which is the main reducing agent.
4
Carbon monoxide reduces iron(III) oxide to molten iron; CO is oxidised to CO2.
5
Limestone is thermally decomposed to calcium oxide (a basic oxide) which neutralises the acidic silicon(IV) oxide (sand) impurity, forming slag, CaSiO3.
6
Molten slag is less dense than molten iron, so it floats and can be run off separately; iron from the furnace (pig iron) contains about 4% carbon and is made into steel.
7
Aluminium is too reactive to be reduced by carbon; purified bauxite (alumina) is electrolysed.
8
(Supplement) Aluminium oxide has a very high melting point (over 2000 °C); dissolving it in molten cryolite lowers the operating temperature to about 950 °C and makes the melt a better conductor, saving energy.
9
(Supplement) At the graphite cathode aluminium ions gain electrons and molten aluminium collects at the bottom; at the graphite anodes oxide ions lose electrons forming oxygen, which reacts with the hot carbon to form carbon dioxide, so the anodes are replaced.
10
(Supplement) Zinc is extracted by roasting zinc blende (ZnS) in air to form zinc oxide and sulfur dioxide, then heating zinc oxide with carbon (coke); zinc vapour is condensed.
Section 2 of 8Process & sequence
- Coke, hematite and limestone are added at the top; hot air is blown in near the bottom.
- Coke burns in airC + O2 → CO2 (exothermic, heats the furnace).
- Carbon dioxide reacts with more cokeCO2 + C → 2CO (carbon monoxide).
- Carbon monoxide reduces iron(III) oxide
- Fe2O3 + 3CO → 2Fe + 3CO2;
- molten iron runs to the bottom.
- Fe2O3 + 3CO → 2Fe + 3CO2;
- Limestone decomposesCaCO3 → CaO + CO2.
- Calcium oxide removes sand impurityCaO + SiO2 → CaSiO3 (slag), which floats on the iron and is tapped off separately.
Extracting aluminium by electrolysiswrite these steps in this order; each step is a marking point.
- Bauxite is purified to aluminium oxide
- Aluminium oxide is dissolved in molten cryolite
- Current passes through graphite electrodes
- Al3+ ions gain electrons at the cathode forming molten aluminium
- O2− ions lose electrons at the anode forming oxygen
- Oxygen reacts with the carbon anodes forming CO2, so anodes are replaced
Section 3 of 8Compare
| Metal | Position relative to carbon | Extraction method |
|---|---|---|
| K, Na, Ca, Mg, Al | above carbon | electrolysis of molten compound |
| Zn, Fe (Pb) | below carbon | reduction of oxide by heating with carbon/carbon monoxide |
| Cu, Ag | low | carbon reduction (or found as compounds that are easily reduced) |
| Au (Pt) | very unreactive | found native (uncombined) |
| Raw material | Contains | Purpose |
|---|---|---|
| Hematite | Fe2O3 | source of iron |
| Coke | C | fuel (heat) and makes CO reducing agent |
| Limestone | CaCO3 | decomposes to CaO, which removes acidic SiO2 as slag |
| Hot air | O2 | burns the coke |
| Feature | Cathode (−) | Anode (+) |
|---|---|---|
| Material | Graphite lining of the steel cell | Large graphite blocks |
| Process | Al3+ gain electrons — reduction | O2− lose electrons — oxidation |
| Product | Molten aluminium, siphoned off | Oxygen gas |
| Problem | — | Carbon reacts with the oxygen (C + O2 → CO2), so anodes are replaced regularly |
Section 4 of 8Worked examples
224 g
Calculate the maximum mass of iron obtained from 320 g of iron(III) oxide (Ar Fe = 56, O = 16).
- Mr Fe2O3 = 2(56) + 3(16) = 160. Moles = 320 ÷ 160 = 2.00 mol.
- Fe2O3 + 3CO → 2Fe + 3CO2, ratio 1 : 2, so 4.00 mol Fe.
- Mass = 4.00 × 56 = 224 g.
52.9 %
Calculate the percentage by mass of aluminium in Al2O3 and the mass of aluminium from 51 tonnes of Al2O3 (Ar Al = 27, O = 16).
- Mr = 2(27) + 3(16) = 102. % Al = (54 ÷ 102) × 100 = 52.9 %. Mass Al = 51 × (54 ÷ 102) = 27 tonnes.
0.60 mol
(Supplement) How many moles of electrons are needed to produce 5.4 g of aluminium at the cathode?
- Al3+ + 3e− → Al. Moles Al = 5.4 ÷ 27 = 0.20 mol. Electrons = 3 × 0.20 = 0.60 mol.
Section 5 of 8Keep going
Extraction of Metals IGCSE Chemistry 0620: what to do next
These Extraction of Metals IGCSE Chemistry 0620 notes covered the key ideas, worked examples and exam technique for this topic. Check your Extraction of Metals IGCSE Chemistry 0620 understanding with the practice questions below, then reread any Extraction of Metals IGCSE Chemistry 0620 point you were unsure about before moving on.
Extraction of Metals IGCSE Chemistry 0620: revision checklist
- Revise the main Extraction of Metals IGCSE Chemistry 0620 definitions until you can write them from memory.
- Practise Extraction of Metals IGCSE Chemistry 0620 exam questions under timed conditions.
- Link each Extraction of Metals IGCSE Chemistry 0620 idea to a diagram or a worked example.
- List the common Extraction of Metals IGCSE Chemistry 0620 mistakes and how to avoid them.
- Explain one Extraction of Metals IGCSE Chemistry 0620 idea out loud as if teaching a friend.
- Summarise Extraction of Metals IGCSE Chemistry 0620 in five key points on a revision card.
- Practice: Extraction of Metals IGCSE Chemistry 0620 practice questions
- Previous lesson: 8.4 Reactivity Series & Corrosion of Metals — 0620 Notes
- Next lesson: 8.6 Water & Water Pollution — 0620 Notes
- Course: Cambridge IGCSE Chemistry 0620 — all units
- Official syllabus: Cambridge IGCSE Chemistry 0620 syllabus
Section 6 of 8Key terms
Section 7 of 8Command terms
Command terms
State / Name
Give a short answer only; no explanation is needed (1 mark = 1 fact).
Define
Give the precise meaning. Learn the syllabus definitions word-for-word: every keyword in the definition is a marking point.
Describe
Say what happens / what the data show, with key features and figures. Do not give reasons.
Explain
Give reasonswhat happens AND why/how, linked with “because”, “so”, “therefore”.
Suggest
Apply knowledge to an unfamiliar situation; any sensible, scientifically-based answer can score.
Compare
Give similarities AND differences, each as a direct comparison (“X is … whereas Y is …”).
Outline
Set out the main points briefly.
Calculate
Work out from given facts; show working, give the unit and the requested significant figures.
Identify
Name/select from given information.
Predict
Give an expected result without a full justification.
Evaluate
Judge the importance or quality of the evidence/method, with reasons.
Section 8 of 8Exam technique
Keywords the mark scheme looks for in this lesson
Keywords the mark scheme looks for in this lesson
Ore · Extraction · Reduction (in extraction) · Hematite · Bauxite · Blast furnace · Coke · Reducing agent · Thermal decomposition · Slag · Cryolite · Electrolysis · Zinc blende
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)
1
Use the exact scientific term and learn syllabus definitions word-for-word.
2
Write “rate of … increases”, not “… increases”.
3
Say “concentration gradient”, never just “gradient”; name particles precisely (atoms, molecules, ions) — never “it”.
4
Give units with every numerical answer and use the significant figures asked for; show all working.
5
Compare = a similarity AND a difference; describe = what happens; explain = why it happens.
6
Repeats let you identify anomalies and calculate a mean — they do not make an experiment “valid”.
Words to avoid
1
carbon reduces iron oxide in the blast furnace (only)carbon monoxide is the main reducing agent that reduces iron(III) oxide to iron
2
limestone removes impuritieslimestone decomposes to calcium oxide, which reacts with silicon dioxide to form slag
3
cryolite is a catalystcryolite is a solvent that lowers the melting point of the electrolyte and improves conductivity, saving energy
4
the anodes wear awayoxygen produced at the carbon anodes reacts with them to form carbon dioxide, so they burn away
5
aluminium is extracted by electrolysis because it is expensivealuminium is more reactive than carbon, so it cannot be reduced by carbon