Extraction and uses of metals
Extraction and Uses of Metals
SB p.160Look around: aircraft overhead, cables strung between pylons, rails, reinforcing bars, coins in your pocket. Metals carry modern life — and almost every one of them began as rock dug out of the ground. Very few occur as the pure element ready to use. The rest are locked into compounds in the Earth's crust, and the branch of chemistry that wins them back is extraction: redox reactions run on an industrial scale, using exactly the reactivity-series logic you built in Chapter 14 (u2:c14).
One idea organises the whole chapter. A metal's position in the reactivity series decides how hard it is to extract — and therefore how it is extracted, and roughly what it costs. Gold sits so low that it can be found native, as the uncombined element, glinting in a pan; iron needs a furnace fed by carbon; aluminium demands huge quantities of electricity. Extraction method, price and even the metal's everyday job all trace back to that one ranking.
The chapter runs in two halves. First, extraction: what an ore is, why carbon can strip oxygen from some metal oxides but not others, why electrolysis takes over above zinc, and how to reason your way through an extraction process you have never seen. Then the payoff: what the extracted metals are actually for — the uses of aluminium, copper, iron and steel, the alloy families (brass, bronze, the steels), and why hammering other elements into a metal makes it harder. Each half is examined every year in Paper 2C, and the command word is usually "explain": explain the method from the position, explain the use from the property, explain the hardness from the structure.
Four earlier chapters load this one. From Chapter 14 (u2:c14) you need the reactivity series itself — especially carbon's reference position — and the redox vocabulary: oxidation as gain of oxygen or loss of electrons, reduction as the reverse, and the agent terms. From Chapter 9 (u1:c09) you need metallic structure: a regular lattice of positive ions surrounded by delocalised electrons, because the explanation of alloy hardness is pure lattice reasoning. From Chapter 10 (u1:c10) you need electrolysis of molten ionic compounds — electrodes, half-equations and which electrode attracts which ion — because that is literally how aluminium is won. Equations throughout assume the balancing and state-symbol skills of Chapter 5 (u1:c05).