How are metals extracted from their ores?

A metal's place in the reactivity series decides how it is extracted. - Metals less reactive than carbon are extracted from their oxides by reduction with carbon, which removes the oxygen Metals more reactive than carbon cannot be extracted this way and need electrolysis Very unreactive metals such…

Reactivity Series and Metal Extraction Notes

AQA GCSE Chemistry: Revision notes

Key facts

Metals react with oxygen to form metal oxides: gaining oxygen is oxidation, losing oxygen is reduction.
Order of reactivity: K, Na, Li, Ca, Mg, Al, (C), Zn, Fe, (H), Cu.
More reactive metals lose electrons and form positive ions more easily.
Metals less reactive than carbon are extracted by reduction with carbon; more reactive metals need electrolysis.
(HT) OIL RIG: Oxidation Is Loss of electrons, Reduction Is Gain.

Metals and oxygen

Metals gain oxygen to form metal oxides, which is oxidation.

Metal + oxygen → metal oxide. For example, $\ce{2Mg + O2 -> 2MgO}$ .

Oxidation is gain of oxygen
Reduction is loss of oxygen

The metal gains oxygen, so it is oxidised.

1
Magnesium ribbon is heated
Mg
2
It reacts with oxygen in the air
bright white flame
3
Magnesium oxide forms
white powder: Mg has gained oxygen, so it is oxidised

Magnesium burning in air is oxidation: it gains oxygen

Oxygen Electrons (HT) Oxidation Gained Lost Reduction Lost Gained

	Oxygen	Electrons (HT)
Oxidation	Gained	Lost
Reduction	Lost	Gained

Oxygen

Oxidation:: Gained
Reduction:: Lost

Electrons (HT)

Oxidation:: Lost
Reduction:: Gained

In $\ce{2Mg + O2 -> 2MgO}$ , what happens to the magnesium?

The reactivity series

Metals are ranked by how vigorously they react with water and dilute acid.

The reactivity series, most to least reactive: potassium, sodium, lithium, calcium, magnesium, aluminium, (carbon), zinc, iron, (hydrogen), copper.

Carbon and hydrogen are not metals. Carbon is used to extract metals, and hydrogen is the reference for reactions with acids.

Metals
Non-metals
Semi-metals

Where the metals of the reactivity series sit: K, Na, Li, Ca, Mg, Al, Zn, Fe and Cu are ringed

Cold water Dilute acid Potassium, sodium, lithium Vigorous, often flames Very vigorous, dangerous Calcium Steady Vigorous Magnesium Very slow Vigorous Zinc, iron Little or none Reacts, slower than Mg Copper None None

	Cold water	Dilute acid
Potassium, sodium, lithium	Vigorous, often flames	Very vigorous, dangerous
Calcium	Steady	Vigorous
Magnesium	Very slow	Vigorous
Zinc, iron	Little or none	Reacts, slower than Mg
Copper	None	None

Cold water

Potassium, sodium, lithium:: Vigorous, often flames
Calcium:: Steady
Magnesium:: Very slow
Zinc, iron:: Little or none
Copper:: None

Dilute acid

Potassium, sodium, lithium:: Very vigorous, dangerous
Calcium:: Vigorous
Magnesium:: Vigorous
Zinc, iron:: Reacts, slower than Mg
Copper:: None

Which of these metals reacts with dilute acid but not with cold water?

Reactivity and ions

More reactive metals lose their outer electrons more easily to form positive ions.

Potassium loses its single outer electron very easily, so it reacts far more violently than copper, which holds its electrons strongly.

You can deduce an order of reactivity from experiments, such as comparing how fast hydrogen fizzes off different metals in the same dilute acid.

Lithium

2,1

Li⁺

Potassium

2,8,8,1

K⁺

2,8,8

Both metals lose their one outer electron to form a 1+ ion; potassium's is further out and held more weakly, so potassium is more reactive

More reactiveloses electrons more easily
Faster fizzing in acidhigher in the series

Magnesium fizzes vigorously in dilute acid but iron fizzes slowly, so magnesium is more reactive than iron.

A metal fizzes faster than zinc in the same acid. Where does it sit in the reactivity series?

Extracting metals

A metal's place in the reactivity series decides how it is extracted.

Metals less reactive than carbon are extracted from their oxides by reduction with carbon, which removes the oxygen
Metals more reactive than carbon cannot be extracted this way and need electrolysis
Very unreactive metals such as gold are found uncombined, so no chemical extraction is needed

1
Find the metal in the series
compare it with carbon
2
Very unreactive, e.g. gold
found uncombined, no extraction
3
Less reactive than carbon
heat the oxide with carbon (reduction)
4
More reactive than carbon
use electrolysis

Choosing an extraction method

Which method extracts iron from iron oxide?

Oxidation and reduction (HT)

Find which substance loses oxygen (reduced) and which gains it (oxidised). Higher tier also uses electrons.

In extraction reactions, the ore loses oxygen (reduction) and the carbon gains it (oxidation).

OIL RIG is the electron definition: Oxidation Is Loss, Reduction Is Gain of electrons. Both definitions describe the same reactions. A more reactive metal can also take the place of a less reactive one in a compound: a displacement reaction.

Mg atom

2,8,2

Mg²⁺

2,8

O atom

2,6

O²⁻

2,8

Mg + O → Mg²⁺ + O²⁻: magnesium loses 2 electrons (oxidised), oxygen gains 2 electrons (reduced)

OILOxidation Is Loss (of electrons)
RIGReduction Is Gain (of electrons)

Worked example

Identify what is oxidised and what is reduced in $\ce{2Fe2O3 + 3C -> 4Fe + 3CO2}$ .

1
Iron(III) oxide loses oxygen to become iron, so it is reduced.
2
Carbon gains oxygen to become carbon dioxide, so it is oxidised.

In $\ce{Fe + Cu^2+ -> Fe^2+ + Cu}$ , what happens to iron?

Try an exam question

Iron is extracted from iron oxide in a blast furnace: $\ce{2Fe2O3 + 3C -> 4Fe + 3CO2}$ . Explain why iron can be extracted using carbon, and state what is reduced.

[4 marks]

That's the notes covered.

Carry on to the next subtopic.