Extraction of metals
Extraction depends on reactivity
- How a metal is taken from its ore depends on its place in the reactivity series.
- Metals below carbon → extracted by heating with carbon (carbon removes the oxygen).
- Metals above carbon → too reactive, so extracted by electrolysis.
Practice
A metal below carbon in the reactivity series is usually extracted by:
Metals below carbon can be reduced by carbon; metals above carbon need electrolysis.
Iron from the blast furnace
- coke (carbon) burns → carbon dioxide + heat,
- carbon dioxide + more carbon → carbon monoxide,
- carbon monoxide reduces iron(III) oxide to iron,
- limestone breaks down to calcium oxide, which removes sandy impurities as slag.
Practice
In the blast furnace, the iron ore is reduced by:
Carbon monoxide reduces iron(III) oxide to iron; limestone removes sandy impurities as slag.
Aluminium by electrolysis
- aluminium oxide is dissolved in molten cryolite to lower the melting point (saves energy),
- at the cathode: aluminium ions gain electrons → aluminium,
- at the anode: oxygen forms and burns away the carbon anodes (so they're replaced).
Practice
Aluminium oxide is dissolved in molten cryolite during extraction to:
Cryolite lowers the melting point of aluminium oxide, saving energy in the electrolysis.
You've got it
Key idea
- below carbon → heat with carbon; above carbon → electrolysis
- blast furnace: carbon monoxide reduces iron ore; limestone removes impurities as slag
- aluminium: electrolysis in molten cryolite; carbon anodes burn away