9.6Metals
Extraction of metals — Combined Science 0653 - Chemistry Revision Notes & Topical Questions
5 min read 9 parts Lesson 11 of 11 Unit quiz
Lesson summary
9.6 Extraction of metals — COMBINED SCIENCE (CHEMISTRY) notes: Relate the ease of extracting a metal from its ore to its position in the reactivity series.Ore — = rock containing enough of a metal to make extraction worthwhile.Native metals — very unreactive metals such as gold a…
- Oxide ores
- Raw materials
- Supplement: electrolyte
- Supplement: electrodes
- Blast furnace
- Native metals — very unreactive metals such as gold and platinum are found uncombined
Section 1 of 9Ores and native metals
Ore
- = rock containing enough of a metal to make extraction worthwhile.
Native metals
- Native metals very unreactive metals such as gold and platinum are found uncombined.
Oxide ores
- Oxide ores hematite is the iron ore and bauxite is the aluminium ore.
Section 2 of 9Extraction as reduction
- Reduction
- extracting a metal from its oxide means removing oxygen.
Section 3 of 9Method and reactivity series
| Position | Metals | Method |
|---|---|---|
| Above carbon | Potassium, sodium, calcium, magnesium, aluminium | Electrolysis of molten compounds, which needs a lot of electricity and is expensive |
| Below carbon | Zinc, iron | Heating with carbon or carbon monoxide |
| Very unreactive | Copper, silver, gold | Often found uncombined or need little processing |
- Ease
- the higher a metal is in the series, the harder it is to extract.
Section 4 of 9Extraction of iron in the blast furnace
Raw materials
- Raw materials hematite, coke (impure carbon) and limestone are added at the top;
- hot air is blown in at the bottom.
Zone 1
- Zone 1 coke burns to form carbon dioxide and provides heat: C + O2 → CO2.
Zone 2
- Zone 2 carbon reacts with carbon dioxide to give carbon monoxide, the main reducing agent: CO2 + C → 2CO.
Zone 3
- Zone 3 carbon monoxide reduces iron(III) oxide to iron: Fe2O3 + 3CO → 2Fe + 3CO2.
- Molten iron collects at the bottom and is tapped off.
Section 5 of 9Removing impurities
Limestone
- Limestone calcium carbonate decomposes: CaCO3 → CaO + CO2.
Slag
- Slag calcium oxide reacts with silicon dioxide impurity: CaO + SiO2 → CaSiO3.
- The molten slag floats on the iron and is tapped off separately.
Section 6 of 9Extraction of aluminium
Method
- Method aluminium is above carbon in the series, so it is extracted by electrolysis.
Supplement
Supplement electrolyte
- purified aluminium oxide is dissolved in molten cryolite to lower the melting point from over 2000 °C.
Supplement
Supplement electrodes
- the cell is steel lined with graphite as the cathode, with graphite blocks as anodes.
Cathode
- Al3+ + 3e- → Al, and molten aluminium collects at the bottom.
Anode
- 2O2- → O2 + 4e-; the oxygen reacts with the graphite anodes to form CO2, so they wear away and are replaced.
Overall
- 2Al2O3 → 4Al + 3O2.
Section 7 of 9More from the specification
Substance
- A material with only one type of particle.
Blast furnace
- Furnace used to extract iron from iron ore.
Section 8 of 9Key terms
| Term | Meaning |
|---|---|
| Ore | Rock containing a metal or its compound worth extracting. |
| Native metal | Metal found uncombined. |
| Blast furnace | Furnace for extracting iron. |
| Slag | Calcium silicate formed from impurities. |
| Cryolite | Molten compound that lowers the melting point of aluminium oxide. |
| Reduction | Removal of oxygen from a compound. |
Section 9 of 9Exam technique
1
Saying aluminium is extracted by heating with carbon — it is above carbon, so electrolysis is needed.
2
Saying extraction is oxidation — it is reduction.
3
Forgetting that limestone removes impurities as slag.
4
Saying iron is reduced by coke directly in zone 3 — carbon monoxide is the reducing agent.
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