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GCSE Chemistry · key term
The presence of an unwanted substance in a sample or on equipment, which can affect a test result.
Used by AQA, Edexcel and OCR
Specification 4.8.3.1 · Paper 2
Unwanted material introduced into a sample or apparatus, which may produce a misleading result.
Revise: Flame TestsSodium produces an especially intense yellow flame, so even a small sodium contamination can hide a weaker colour such as potassium's lilac.
Specification 9.2C · Paper 2
The unwanted presence of another substance in a sample or on the apparatus, which may produce a misleading result.
Specification C4.2c, C4.2e · Paper 2 (Foundation), Paper 4 (Higher)
Unwanted material in a sample or on apparatus that can alter the observed result.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
The presence of an unwanted substance in a sample or on equipment, which may affect a test result.
Revise: Flame tests techniqueDifferent metal elements can produce different colours, but even a small amount of another substance may interfere: sodium contamination, for example, produces a strong yellow colour that can hide a weaker one. A matching flame colour is therefore useful evidence for a metal ion, especially for a single unknown salt, but an unclear or mixed colour should not be treated as a certain identification.
A yellow flame can result from sodium contamination, so mention cleaning the wire if a method or reliability question is asked.
In a method question, describe cleaning the wire loop before testing the sample; contamination can change the flame colour.
A persistent yellow colour can result from sodium contamination. Interpret an unexpected result cautiously rather than assuming that every sample contains sodium.
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