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GCSE Biology · key term
A substance added to a sample to produce a chemical reaction that can reveal whether another substance is present.
Used by Edexcel and OCR
Specification 1.13B · Paper 1, Paper 2
Revise: Food Tests InvestigationFoods may contain several kinds of biological molecule. Their presence cannot always be recognised just by looking at the food, so chemical reagents are used. A reagent reacts with a particular type of substance and produces an observable result, such as a colour change, precipitate or emulsion.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
A chemical used to reveal whether a particular substance is present, usually through a visible change.
Name both the reagent and the positive observation: for example, “iodine solution changes from yellow-brown to blue-black”, not simply “it changes colour”.
Describe both the reagent and the observed result. Heating is needed for Benedict’s test but not for the iodine or Biuret tests.
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A qualitative food test uses a reagent and an observable result to identify one kind. It tells you whether that substance is present, rather than giving a precise measurement of its amount. If the food is in large pieces, cut or grind a small sample, then mix it with a little distilled water in a test tube.
A chemical added to a sample to test for a particular substance.