Edexcel Biology GCSE - CP 3 - Food tests - Practical notes

Sep 5, 2026

Practical notes for Edexcel Biology GCSE CP 03 focus on conducting qualitative chemical tests to identify major nutrients: starch, reducing sugars, proteins, and lipids. The procedure details the iodine test, Benedict’s test, Biuret test, and an emulsion test using ethanol and distilled water. Expected colour changes and observations are specified, and guidance covers recording results, potential errors from subtle colour shifts, and safety precautions for hot water baths, biuret reagents, and flammable ethanol.

LanguageEnglish

CategoryExam

FormatPDF

Pages3

Reading Time8 min

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Food tests

Aim

The Iodine test for starch

The Benedict’s test for reducing sugars

Test for protein

Test for lipids

Sources of error

Safety precautions

Edexcel Biology GCSE CP 03: Food testsPractical notes # Food tests Aim Conduct qualitative chemical tests for starch, reducing sugars, proteins, and lipids. ## The Iodine test for starch Equipment ● Food sample ● A test tube ● Iodine solution (0.01 mol/dm3) ● Pipettes. Method 1. Put some of the food sample into a test tube. 2. Add a few drops of iodine solution to the food sample using a pipette. 3. If starch is present, the solution turns from brown to blue-black. Note any colour change in atable of results. ## The Benedict’s test for reducing sugars Equipment ● Food sample ● A test tube ● Benedict’s solution ● Hot water bath ● Thermometer ● Pipettes Method 1. Add an equal volume or excess of Benedict’s solution to the food sample in a test tube. 2. Place in a hot water bath for a few minutes. 3. If reducing sugar is present, a brick red precipitate is formed. If reducing sugar is absent,the solution remains blue. Note any colour change in a table of results. # Test for protein Equipment ● A test tube ● A 10cm3 measuring cylinder ● Biuret solution Method 1. Add a few drops of Biuret’s reagent (sodium hydroxide and copper (II) sulphate) to the foodsample in a test tube. 2. Shake the solution to mix and wait for a few minutes. 3. If protein is present, the solution turns from blue to purple. # Test for lipids Equipment ● Food sample ● Test tube ● Ethanol ● Distilled water Method 1. Add a few cm3 of ethanol to the food sample. 2. Pour this mixture into a test tube of equal volumes of distilled water. 3. If lipids are present, a white emulsion is formed on the surface of the mixture. 4. This is called the emulsion test. # Sources of error Colour change of Benedict’s test and Biuret test may be subtle and difficult to judge if theconcentration of the tested molecule is low. # Safety precautions Tie hair back and wear safety goggles when performing the Benedict’s test using a Bunsen burnerand hot water bath. Handle Biuret solution with care as it contains copper sulphate (poisonous) and sodium hydroxide(corrosive) . Wash immediately if it comes into contact with skin and wipe away any spills onsurfaces. Keep ethanol solution away from flames as ethanol is highly flammable.

FAQs

What is the aim of these food tests in the notes?

The aim is to carry out qualitative chemical tests to detect starch, reducing sugars, proteins, and lipids in food samples.

How do you carry out the iodine test for starch and what result indicates starch?

Add iodine solution to the food sample. If starch is present, the brown solution turns blue-black, and any colour change should be recorded.

What safety precautions are required for these tests?

Tie hair back and wear safety goggles for the Benedict’s test with a hot water bath. Handle biuret solution carefully because it contains copper sulphate and sodium hydroxide, and keep ethanol away from flames due to its flammability.

Sep 5, 2026

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