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GCSE Chemistry · key term
A substance containing only one element or one compound.
Used by AQA, Edexcel and OCR
Specification 4.8.1.1 · Paper 2
A single element or a single compound that is not mixed with any other substance.
Revise: Pure SubstancesIn chemistry, a pure substance is a single element or a single compound, with no other substance mixed into it. A sample containing only iron is pure because iron is one element. A sample containing only water is also pure, even though each water molecule contains both hydrogen and oxygen atoms: water is one compound.
Specification 2.5, 2.6 · Paper 1
A material containing only one element or one compound, with no other substances mixed in.
A substance containing only one element or one compound, with the same composition throughout.
Specification C2.1a, C2.1b, C2.1e, C2.1k · Paper 1 (Foundation), Paper 3 (Higher)
A sample containing only one chemical substance: either one element or one compound.
Revise: Defining PurityA pure substance contains only one chemical substance.
A substance containing only one element or one compound, rather than a mixture of substances.
A single element or compound that is not mixed with any other substance.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
A material that contains only one element or only one compound, with no other substances mixed with it.
Revise: Purity definitionA pure substance contains only one element or only one compound. There are no other substances mixed with it.
A substance consisting of just one element or one compound, rather than a mixture.
Avoid claiming that every impurity changes a boiling point in the same direction. The reliable distinction is a specific temperature for a pure substance compared with a range for a mixture.
In a melting-point table, a single sharp temperature indicates a pure substance; a start-to-finish range indicates a mixture.
When interpreting data, use both features: a pure substance melts at or very close to its known melting point and over a narrow range; an impure sample usually melts at a lower temperature and over a wider range.
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