Chemical Tests for Biomolecules

Free Chemical Tests for Biomolecules revision notes for OCR A Level Biology – covering specification points 2.1.2(q) and 2.1.2(r).

Biochemical tests can either be qualitative or quantitative.

Qualitative tests only give a positive or negative response, allowing you to identify a substance.

Quantitative tests allow you to determine the concentration of a substance in a solution.

The table below provides an overview of the different qualitative tests for identifying biological molecules:

Chemical	Reagent(s) Used	Positive Result	Negative Result
Biuret Test (Proteins)	Biuret reagent (or NaOH → CuSO₄)	Lilac	Stays blue
Benedict’s Test (Reducing Sugars)	Benedict’s reagent (+ 80 °C heat)	Green → Yellow → Orange → Brick-red	Stays blue
Benedict’s Test (Non-Reducing Sugars)	HCl (hydrolysis) + NaHCO₃ → Benedict’s reagent (+ 80 °C heat)	Green → Yellow → Orange → Brick-red	Stays blue
Iodine Test (Starch)	Iodine solution	Blue-black colour	Yellow-brown (no starch)
Emulsion Test (Lipids)	Ethanol → Water	Cloudy white emulsion	Solution remains clear

Want to dive deeper?