How do we get a metal out of its ore, and why does the method depend on reactivity?
Extraction of metals: ores, how the method of extraction depends on the reactivity series, reduction by heat, reduction by carbon or carbon monoxide, and electrolysis for very reactive metals.
An SQA National 5 Chemistry answer on the extraction of metals from ores, covering how the method depends on the reactivity series, extraction by heat alone, reduction by carbon or carbon monoxide, and electrolysis for the most reactive metals.
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What this key area is asking
The SQA wants you to explain that metals are usually found as compounds in ores, that the method of extraction depends on the reactivity of the metal, and to describe extraction by heat alone, reduction by carbon or carbon monoxide, and electrolysis for the most reactive metals. It applies the reactivity series from the metals key area to industry.
Ores and why most metals are combined
The least reactive metals, such as gold and silver, are found as the uncombined metal because they do not react readily with anything.
The method depends on reactivity
Reduction by carbon
For a metal below carbon in the reactivity series, heating the metal oxide with carbon (or the carbon monoxide it forms) removes the oxygen. This is reduction, because the metal ions gain electrons and the oxygen is taken away. For example, in the blast furnace, iron oxide is reduced to iron:
Electrolysis for reactive metals
Worked example: choosing a method
Examples in context
The reactivity series explains the timeline of human history. Gold and copper, low in the series, were used first because they are easy to find uncombined or easy to extract. Iron came later, once furnaces hot enough for carbon reduction were built, giving the Iron Age. Aluminium, though very common in the Earth's crust, was once more precious than gold because there was no way to extract it until electrolysis was developed, which is why it now depends on cheap electricity.
Try this
Q1. Define the term ore. [1 mark]
- Cue. A naturally occurring rock or mineral containing enough metal compound to make extraction worthwhile.
Q2. Name the method used to extract a metal more reactive than carbon. [1 mark]
- Cue. Electrolysis.
Q3. Explain why gold is found as the uncombined metal. [2 marks]
- Cue. Gold is very unreactive, so it does not combine with oxygen or other elements to form compounds.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA N5 2019 style3 marksExplain why aluminium is extracted by electrolysis but iron can be extracted by heating its ore with carbon. Refer to the reactivity series in your answer.Show worked answer →
Markers reward the link to reactivity for each metal and the matching method.
The method of extraction depends on how reactive the metal is. Aluminium is a very reactive metal, high in the reactivity series and above carbon, so carbon cannot remove the oxygen from its ore. The strong bonds in aluminium oxide can only be broken by electrolysis, which uses electricity to reduce the metal ions.
Iron is less reactive than aluminium and lies below carbon in the reactivity series, so carbon (or carbon monoxide) can reduce iron oxide by removing the oxygen when the ore is heated, which is cheaper than electrolysis. The general rule is that the more reactive the metal, the harder and more expensive it is to extract.
SQA N5 2021 style3 marksGold is found in the Earth as the metal itself, while most metals are found as compounds in ores. Explain this difference, and define the term ore.Show worked answer →
A 3 mark answer needs the reason gold is uncombined, the reason most metals are combined, and a definition of ore.
Gold is found as the uncombined metal because it is very unreactive, so it does not react with oxygen, water or other substances to form compounds. It stays as the pure element.
Most metals are reactive enough to combine with other elements, especially oxygen, so they are found as compounds, usually metal oxides, rather than as the pure metal.
An ore is a naturally occurring rock or mineral that contains enough of a metal compound to make it worth extracting the metal from it.
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Sources & how we know this
- SQA National 5 Chemistry Course Specification — SQA (2019)