Extracting Metals from their Ores

What this lesson covers in the specification

Incandio is aligned to this specification. It is not published by, endorsed by or affiliated with Pearson, and it reproduces none of Pearson's wording — the statement numbers are given so you can check every lesson against your own copy.

• 2.22 — Most metals are extracted from ores; unreactive metals occur uncombined (bold C statement — Paper 2 only)
• 2.23 — How extraction method relates to position in the reactivity series (carbon for iron, electrolysis for aluminium) (bold C statement — Paper 2 only)
• 2.24 — Commenting on a metal extraction process from given information (bold C statement — Paper 2 only)

1 · Understand it

No exam language yet. The only question this section answers is: do I actually understand what is happening?

Almost every metal is found in the ground as a COMPOUND rather than as the metal itself, usually an oxide or a sulfide, and a rock containing enough of it to be worth mining is called an ORE. The reason is the whole of the previous pages: a reactive metal has long since reacted with whatever was available, and the compound is where it ended up.

The exceptions prove the point. GOLD and SILVER are found NATIVE — as the uncombined metal — precisely because they are so unreactive that nothing in the ground could attack them. That is why gold was among the first metals humans used, thousands of years before iron: it required no extraction at all, only picking up.

Statement 2.23 — the series read as an instruction

1. A metal BELOW carbon in the reactivity series can be extracted by REDUCTION WITH CARBON, because carbon is more reactive and will take the oxygen away from it.
2. Iron, zinc, tin, lead and copper are all below carbon, and all are extracted this way — iron in a blast furnace.
3. A metal ABOVE carbon cannot be extracted this way, because carbon is not reactive enough to take the oxygen from a metal that holds it more strongly.
4. Those metals must be extracted by ELECTROLYSIS of the molten compound, which needs no reagent more reactive than the metal — only electricity.
5. Aluminium, magnesium, calcium, sodium and potassium are all above carbon, and all are obtained by electrolysis.
6. So carbon's position in the series is not a curiosity. It is the dividing line between a cheap extraction and an expensive one.

Think of it like getting something back from someone who will not give it up

If a friend is holding your book loosely, you can offer them something they want more and they will hand it over — a trade, and it costs you very little. If they are holding it in a locked safe and want nothing you have, no trade will work and you have to force the safe, which is expensive and needs equipment. Carbon reduction is the trade: carbon wants the oxygen more than the metal does, so it takes it. Electrolysis is forcing the safe: nothing available wants the oxygen enough, so electricity is used to pull the compound apart directly. That difference in cost is why aluminium was once more valuable than gold and is now used for drink cans.

In the blast furnace the reaction is iron(III) oxide + carbon monoxide → iron + carbon dioxide, or Fe₂O₃ + 3CO → 2Fe + 3CO₂. It works because iron is below carbon, so the carbon can take the oxygen away from it.

That is a redox reaction described in the language of the previous page: the iron oxide is REDUCED, losing its oxygen, and the carbon monoxide is OXIDISED, gaining it. Carbon is therefore the REDUCING AGENT, and the reason it works is exactly that it sits above iron in the series.

Aluminium is the standard example of the other route, and it illustrates why the distinction is expensive. Aluminium oxide melts at over 2000 °C, so it is dissolved in molten cryolite to bring the working temperature down to around 950 °C — a saving of over a thousand degrees, and one of the most important pieces of process engineering in industrial chemistry. Even so, the process consumes enormous amounts of electricity, which is why aluminium smelters are built where electricity is cheap and why recycling aluminium saves about 95% of the energy of making it new.

Statement 2.24 — commenting on a process you have not met

Titanium is above carbon in the reactivity series. Its ore is converted to titanium chloride, which is then heated with sodium in an inert argon atmosphere. Comment on why this method is used and why titanium is expensive.

1. Titanium is ABOVE carbon, so reduction with carbon will not work — carbon cannot take the chlorine or oxygen from it.
2. Sodium is used because sodium is MORE reactive than titanium, so it can displace it. This is a displacement reaction, the same chemistry as the reactivity series pages.
3. But sodium is itself obtained by electrolysis, because sodium is above carbon too. So the process contains a hidden electrolysis and all of its cost.
4. The argon atmosphere is needed because both sodium and hot titanium would otherwise react with the oxygen and nitrogen in air.
5. So titanium is expensive because the extraction is a multi-stage batch process requiring an expensive reactive metal, an inert atmosphere and, indirectly, electrolysis.

Answer: Carbon cannot reduce it; a more reactive metal is used instead, and that metal's own extraction is what makes titanium costly.

That question is the shape statement 2.24 takes: you are given a process for a metal you have never studied and asked to comment sensibly. Everything needed is on this page — where the metal sits relative to carbon, whether the reagent used is more reactive than it, and what the conditions are protecting against.

One general point worth carrying into any such question. Extraction always costs energy, because you are undoing a reaction that happened spontaneously over geological time. The more reactive the metal, the more strongly it holds its compound, and so the more energy is needed to reverse it. Cost, position in the series, and difficulty of extraction are three descriptions of one fact.

2 · Grade 9 Notes

A different job from the section above. You have already understood it; this is the precise set of things to LEARN — definitions to reproduce word for word, processes in order, equations with units, and the answers that score full marks.

The vocabulary of extraction

Ore

A rock containing enough of a metal compound to make extraction worthwhile.

Native metal

A metal found uncombined in the ground, because it is too unreactive to have formed compounds — gold and silver.

Reduction

Removal of oxygen from a compound, or gain of electrons. Extracting a metal from its oxide is always a reduction.

Cryolite

The molten compound in which aluminium oxide is dissolved, lowering the working temperature from over 2000 °C to about 950 °C.

Statement 2.23 — which method, and why

Statement 2.24 — commenting on an extraction process

1. Find the metal's position relative to CARBON in the reactivity series.
2. Below carbon: expect reduction with carbon, and a relatively cheap process.
3. Above carbon: expect electrolysis, or displacement by an even more reactive metal, and a costly process.
4. If another metal is used as the reagent, check it is MORE reactive than the one being extracted.
5. Ask what any unusual conditions are for — an inert atmosphere excludes oxygen and nitrogen; a solvent such as cryolite lowers the temperature.

Why extraction costs what it does

• Extraction UNDOES a reaction that happened spontaneously, so it always costs energy
• The more REACTIVE the metal, the more strongly it holds its compound and the more energy is needed
• GOLD and SILVER need no extraction at all — they are found native
• ALUMINIUM smelting uses enormous amounts of electricity, so recycling saves about 95% of the energy
• Cost, position in the series and difficulty of extraction are three descriptions of one fact

Model answer [4 marks]

Explain why iron is extracted using carbon but aluminium is extracted by electrolysis. [4]

Iron is below carbon in the reactivity series, so carbon is more reactive than iron and is able to take the oxygen away from iron oxide, reducing it to iron. This makes reduction with carbon a suitable and relatively cheap method for iron. Aluminium is above carbon in the reactivity series, so carbon is not reactive enough to remove the oxygen from aluminium oxide and the reaction would not occur. Aluminium must therefore be extracted by electrolysis of its molten compound, which does not depend on any reagent being more reactive than the metal but does require a large amount of electricity.

Model answer [3 marks]

Explain why gold is found as the uncombined metal in the ground, while iron is not. [3]

Gold is very low in the reactivity series and is extremely unreactive, so it does not react with oxygen, water or other substances in the ground and remains as the uncombined metal. Iron is much higher in the reactivity series and is far more reactive, so over long periods it reacts with oxygen and other substances to form compounds. Iron is therefore found as an ore, from which it must be extracted, whereas gold can be used as it is found.

Not this: Aluminium is extracted by electrolysis because aluminium oxide has a very high melting point.

This: The melting point is a practical difficulty, solved by dissolving the oxide in cryolite. The REASON electrolysis is needed is that aluminium is ABOVE CARBON in the reactivity series, so carbon cannot take its oxygen away.

Mark-losing trap. CARBON'S POSITION is the dividing line: below it, reduce with carbon; above it, electrolyse.

Mark-losing trap. Cryolite lowers the TEMPERATURE. It is not the reason electrolysis is used.

Mark-losing trap. Gold and silver are found NATIVE because they are unreactive — no extraction is needed at all.

3 · Prove it — the five questions

The five questions climb Grade 6 → Grade 7 → Grade 8 → Grade 9 → Grade 9 challenge, and are marked inside Incandio on your own device, by rule, with an authored diagnosis of the mistake you actually made. The mark schemes stay in the app so that the practice is worth doing; the questions themselves are here.

1. Grade 6 · State [1 mark] — Why is gold found in the ground as the uncombined metal?
2. Grade 7 · Predict [2 marks] — Zinc is below carbon in the reactivity series. Which method would be used to extract zinc from zinc oxide?
3. Grade 8 · Explain [3 marks] — Explain why aluminium cannot be extracted by heating aluminium oxide with carbon.
4. Grade 9 · Explain [6 marks] — Select every statement that belongs in a full-mark explanation of why the method used to extract a metal depends on its position in the reactivity series.
5. 9+ · Analyse [6 marks] — A student reads that titanium, which is above carbon in the reactivity series, is extracted by heating titanium chloride with sodium. They conclude that this contradicts the rule that metals above carbon must be extracted by electrolysis. Select every statement that belongs in a full-mark analysis.

The people behind this science

Two ways into the same idea — the one who opened the route for every metal carbon could not touch, and the one who established that an ore is a compound at all. Inside Incandio each of them answers knowing exactly which lesson you have just finished.

Humphry Davy — the one who opened the route for every metal carbon could not touch

This page's division between carbon reduction and electrolysis is Davy's discovery stated as industrial practice. Potassium and sodium had resisted every chemical attempt at extraction precisely because they are above everything that might have displaced them, and Davy's insight was that electricity needs no reagent at all — it supplies the electrons directly. Every aluminium smelter in the world is running his method at scale. He is the right person to ask why some compounds simply cannot be opened by chemistry, and what made him think a battery would succeed where reagents had failed.

• “Why could no chemical reagent free potassium from its compound?”
• “What made you think electricity would succeed instead?”
• “How is electrolysis different from a displacement reaction?”
• “Which metals did you expect to yield, and which surprised you?”
• “Did you imagine this being done on an industrial scale?”

Antoine Lavoisier — the one who established that an ore is a compound at all

Calling an ore 'a metal combined with oxygen' presupposes Lavoisier's whole account. Under phlogiston theory the relationship ran the other way: the ore was the simple substance and the metal was the ore plus phlogiston, so smelting ADDED something rather than removing it. Lavoisier's weighings showed that the metal is lighter than its oxide, so smelting must remove something — the oxygen. That inversion is what makes extraction a REDUCTION, and it is why the reactivity series can predict which reagent will work.

• “What is an ore, in terms of what it is made of?”
• “What did people think smelting was doing before you?”
• “How did weighing settle which way round the relationship goes?”
• “Why is a metal lighter than its ore?”
• “What does it mean to say extraction is a reduction?”

Then defend it

On Incandio a lesson is not finished when the questions come out right. You teach the idea back to Ember, an AI apprentice who asks the awkward question, and then you argue it against Humphry Davy in a structured debate marked against descriptors you can read before you enter. Learn it, teach it, then defend it — all three happen on this page once the app loads.

Carry on through the course

• Previous lesson: Redox
• Next lesson: Uses of Metals, and Alloys
• Group 1 — the Alkali Metals — Metals soft enough to cut with a knife, which set fire to water — and get worse as you go down.
• Group 7 — the Halogens — A green gas, a brown liquid and a grey solid — and a trend that runs the opposite way to Group 1.
• The Gases in the Air — Four gases, one of which is doing almost all the chemistry — and how to measure it without ever touching it.
• Combustion and Carbonates — Three things burning in oxygen, one carbonate breaking apart, and the 0.04% gas that changes the climate.
• The Reactivity Series — Putting eleven metals in order by watching what each one will and will not do.
• All of Chemistry · Incandio Science