(e) Extraction and uses of metals
- Syllabus
- 2024
- Topic
- —
- Level
- —
Learning objectives
222C Metal ores and native metalsKnow that most metals are extracted from ores found in the Earth’s crust and that unreactive metals are often found as the uncombined element223C Extraction method and reactivityExplain how the method of extraction of a metal is related to its position in the reactivity series, illustrated by carbon extraction for iron and electrolysis for aluminium224C Evaluating metal extraction processesBe able to comment on a metal extraction process, given appropriate information detailed knowledge of the processes used in the extraction of a specific metal is not required225C Uses of aluminium, copper, iron and steelExplain the uses of aluminium, copper, iron and steel in terms of their properties the types of steel will be limited to low-carbon (mild), high-carbon and stainless226C AlloysKnow that an alloy is a mixture of a metal and one or more elements, usually other metals or carbon227C Why alloys are harderExplain why alloys are harder than pure metals
Relate metal reactivity to how it occurs in the Earth
Most metals in the Earth's crust occur chemically combined with other elements in ores. Extraction separates the useful metal from its compounds and the rest of the ore.
| Metal behaviour | How it is commonly found | Why |
|---|---|---|
| reactive metal | as a compound in an ore | it has readily reacted with substances in the environment |
| unreactive metal | sometimes as the uncombined, native element | it is less likely to have formed a compound |
Gold is very unreactive, so it may be found native. A metal being present in an ore does not mean the ore is made only of that metal; it contains metal compound and other material.
Unreactive metals are often—not always—found uncombined, and most metals still require extraction from ores. 'Native' means the element is uncombined, not that it is pure enough to use without separation.
Choose extraction by position relative to carbon
The reactivity series determines whether carbon can remove oxygen from a metal oxide. Metals below carbon can be extracted by reduction with carbon or carbon monoxide; metals above carbon require electrolysis of a molten compound.
| Example | Position relative to carbon | Suitable method | Reason |
|---|---|---|---|
| iron | below carbon | carbon extraction | carbon removes oxygen from iron oxide |
| aluminium | above carbon | electrolysis | carbon cannot displace aluminium from aluminium oxide |
\ce{Fe2O3 + 3CO -> 2Fe + 3CO2}\qquad\ce{Al^{3+} + 3e^- -> Al}
Electrolysis must use a molten aluminium compound so its ions can move; an aqueous solution would not produce aluminium metal. This objective uses iron and aluminium to illustrate the rule, not to require detailed knowledge of a blast furnace or industrial cell.
Evaluate an extraction process from supplied evidence
To comment on an unfamiliar extraction process, convert the supplied information into linked advantages, disadvantages and a qualified judgment. Detailed recall of a named industrial process is not required.
| Supplied information | Evidence-based comment |
|---|---|
| energy or temperature | lower energy demand may reduce operating cost and fuel use |
| yield or metal recovered | a higher yield gives more useful metal from the same input |
| purity | higher purity may suit demanding uses but may need extra processing |
| raw-material or equipment cost | abundant inputs or simpler equipment may make the process cheaper |
| emissions, waste, land or water effects | less pollution or waste reduces environmental impact |
| recycling data | recycling may use less ore and energy, but collection and separation still have impacts |
A strong conclusion states the deciding criterion and uses comparative data when supplied: for example, one method may use less energy but recover less metal, so the preferred method depends on whether cost, yield or environmental impact has priority.
Do not invent missing temperatures, costs or emissions. A process is not automatically 'best' because it wins on one measure; acknowledge any material trade-off shown by the information.
Link each metal or steel use to a property
A use is explained only when the relevant property is linked to what the object must do. Different steels have different carbon or alloy content, so they should not be treated as one material.
| Material | Relevant properties | Property-linked uses |
|---|---|---|
| aluminium | low density, corrosion resistant, malleable, conducts heat and electricity | aircraft need low mass; cans and foil need shaping; pans and cables need conduction |
| copper | excellent electrical and thermal conductor, ductile, corrosion resistant | wires need conduction and drawing; water pipes need corrosion resistance; cookware needs heat transfer |
| iron | relatively soft and malleable but rusts unless protected | gates, railings and shaped ironwork use its formability |
| low-carbon (mild) steel | strong, tough and relatively malleable | car bodies, nails and structural shapes need strength with shaping |
| high-carbon steel | harder, stronger and less malleable | cutting tools, blades and drill bits need a hard edge |
| stainless steel | hard and corrosion resistant | cutlery, sinks and chemical equipment must resist wear and corrosion |
Do not give a property without explaining its relevance: 'aluminium is used for aircraft because it is low density' is linked; 'because it is a metal' is not. Hardness, strength, toughness and malleability are different properties.
Define an alloy as a mixture containing a metal
An alloy is a mixture of a metal with one or more other elements. The added elements are usually other metals or carbon.
| Alloy | Main metal | Other element or elements |
|---|---|---|
| steel | iron | carbon |
| stainless steel | iron | chromium and often nickel, plus carbon |
| magnalium | aluminium | magnesium |
Because an alloy is a mixture, its elements are not combined in one fixed chemical formula. Changing their proportions can change the alloy's properties.
An alloy is not necessarily a mixture of metals only: steel contains the non-metal carbon. It is not a compound, and 'two or more elements' is incomplete unless at least one is a metal.
Explain why alloys resist layer movement
In a pure metal, equal-sized atoms or positive ions form regular layers that can slide over one another when a force is applied. This makes many pure metals relatively soft and malleable.
| Structure | Arrangement under force | Result |
|---|---|---|
| pure metal | regular layers of similarly sized particles slide more easily | softer and easier to shape |
| alloy | differently sized particles distort the regular layers and obstruct sliding | harder to deform |
Different-sized particles → disrupted regular arrangement → layers cannot slide as easily → a larger force is needed to change shape. Metallic bonding remains; hardness does not arise because the alloy becomes an ionic or molecular substance.
Hardness means resistance to scratching or permanent shape change. It is not identical to strength or toughness, and the explanation must mention disrupted layers and reduced sliding rather than simply saying that atoms are 'packed tighter'.