OCR GCSE Biology food tests- B2

preparing a sample (especially for solid foods)

1. break up the food using a pestle and mortar

2. transfer to a test tube and add distilled water

3. mix the food with water by stirring with a glass rod

4. filter the mixture using a funnel and filter paper

test for glucose (a reducing sugar)

1. add benedict’s solution to sample solution in a test tube

2. heat in boiling water bath for 5 minutes

3. take out the test tube and observe the colour

4. a positive test for glucose will show a colour change from blue to orange / brick red

test for starch using iodine

1. add drops of iodine solution to the food sample

2. positive test will show a colour change from orange- brown to blue-black

test for protein

1. add drops of Biuret solution to the food sample

2. a positive test will show a colour change from blue to violet/ purple

test for lipids

1. mix food sample with 2cm³ of ethanol and shake

2. allow time for the sample to dissolve in the ethanol

3. strain the ethanol solution into another test tube

4. add the ethanol solution to an equal volume of cold distilled water (2cm³)

5. a positive test will show a cloudy emulsion forming. if negative, it will turn colourless

food test results table

important hazards

• biuret solution contains copper (II) sulfate- dangerous

  • solution: wear goggles

• iodine is an irritant to the eyes

  • solution: wear goggles

• sodium hydroxide in buiret solution is corrosive

  • solution: wash your hands immediately

• ethanol is highly flammable

  • keep it away from a bunsen burner