2eExtraction and uses of metals

Separate Chemistry only.

Ores

An ore is a rock containing enough of a metal compound to make extraction worthwhile.

Those last words are part of the definition. Almost every rock contains traces of most metals; what makes something an ore is that there is enough to extract profitably. It is an economic judgement as much as a chemical one.

Why most metals are found combined

Metals react with oxygen and other elements over geological time, so nearly all are found as compounds.

The exceptions are the least reactive: gold, silver and platinum are found as the uncombined element, because they are so unreactive that they do not readily combine with oxygen or other elements in the ground.

(Not that they cannot react at all — they can, under the right conditions. They simply do not, in nature.)

How a metal is found is therefore direct evidence of its reactivity.

Which extraction method?

One comparison decides it: is the metal above or below carbon in the reactivity series?

Carbon sits between aluminium and zinc, so that boundary is where the methods change.

Why carbon works for iron

Carbon is more reactive than iron, so it can take the oxygen away:

Fe₂O₃ + 3CO → 2Fe + 3CO₂

The iron(III) oxide is reduced — it loses oxygen. The carbon monoxide is the reducing agent.

Why it fails for aluminium

Aluminium is more reactive than carbon, so carbon cannot displace it from its oxide. There is no cheaper route available, so electrolysis it must be.

That is the whole reason aluminium was once more valuable than gold, and why it stayed expensive until cheap electricity arrived.

The cost, and why it is accepted

Electrolysis uses vast amounts of electricity. It is used anyway because aluminium's properties — low density, corrosion resistance — make it worth the cost, and because recycling uses about 5% of the energy of extracting it fresh.

Separate Chemistry only.

Every use of a metal traces back to a property. Questions ask you to make that link explicitly — naming the property alone rarely earns full marks.

Aluminium

Aluminium is high in the reactivity series, so its corrosion resistance looks puzzling. The reason is a layer of aluminium oxide that forms instantly on the surface and then blocks any further reaction. The metal is reactive; the oxide layer protects it.

Copper

Ductile means it can be pulled into a wire; malleable means it can be hammered into shape. The two words are not interchangeable.

Iron and steel

Steel is chosen for bridges and buildings because it is strong, hard-wearing and, for a bulk material, cheap enough to use in quantity.

Types of steel

More carbon makes steel harder but more brittle. Both consequences matter: high-carbon steel keeps a sharp edge, and would shatter as a car body.

Low-carbon steel and mild steel are the same material under two names.

Commenting on a process

When asked to comment on an extraction process, the question wants the trade-off, not only the chemistry: cost, energy, availability of the ore, and whether recycling offers a cheaper route.

Separate Chemistry only.

An alloy is a mixture of a metal with one or more other elements, usually other metals or carbon.

The word mixture is the one that carries the marks. Calling an alloy a compound is the commonest error here, and it is wrong for a specific reason: the components are not chemically bonded, and the proportions can be varied.

That variability is the point. Steel is not one substance — choosing how much carbon to add is how you get mild steel or high-carbon steel from the same two elements.

Why alloys are harder

This explanation is worth learning as a sequence, because each step earns its own mark.

1. In a pure metal, all the atoms are the same size and sit in regular layers.
2. Those layers can slide over one another easily, which is why a pure metal is soft.
3. In an alloy, the added atoms are a different size.
4. They disrupt the regular arrangement of the layers.
5. So the layers can no longer slide easily, and the alloy is harder.

The counter-intuitive bit

A less regular structure is harder. Students often assume a neater arrangement would be stronger; here the opposite is true, because regularity is exactly what allows sliding.

So the explanation must name the different size of the added atoms. "The atoms are held together more strongly" is not the reason and is not credited.

Alloys still conduct

An alloy is held by metallic bonding, with delocalised electrons, so it still conducts electricity and heat. Alloying changes the hardness, not the type of bonding.

Brass

Brass is copper mixed with zinc. It is harder than pure copper because the zinc atoms are a different size, and it resists corrosion — which is why it is used for musical instruments and door fittings.