This is a mind map on the 4 different food tests required to learn at GCSE level. It has all the information about how to create a food sample, the equipment needed, the method used for each type and safety hazards. It is a great resource and also has a summary - on top of that it's aesthetic!
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Aim The Iodine test for starch
Conduct qualitative chemical tests for starch, reducing sugars, proteins,The emulsion test for lipids Equipment
and lipids. Equipment - 5cm3 Food sample
- 1cm3 Food sample - A test tube
Safety precautions - Iodine solution
- Test tube
- Tie hair back and wear safety goggles when performing the Benedict’s - Pipettes.
- 2cm3 Ethanol
test using a Bunsen burner and hot water bath.
- Distilled water Method
- Handle Biuret solution with care. It contains copper sulphate
Method 1. Put 5cm3 of your food sample into a test tube.
(poisonous) and sodium hydroxide (corrosive). Wash immediately if
comes into contact with skin and wipe away any spills to surfaces. 1. Add a 2cm3 of ethanol to the food sample. 2. Add a few drops of iodine solution to the food sample using a
- Keep ethanol solution away from flames as ethanol is highly flammable. 2. Pour this mixture into a test tube of equal volumes of distilled water. (half pipette and gently shake the tube.
a test tube. 3. If starch is present, the solution turns from browny - orange to
Preparing a food sample 3. If lipids are present, a white emulsion is formed on the surface of the blue-black.
1. Get a piece of your food and break it up using a pestle and mortar mixture.
2. Transfer the ground up food to a beaker and add some distilled water
3. Give the mixture a good stir with a glass rod to dissolve some of the
food
4. Filter the solution using a funnel lined with filter paper. This will get rid
of all the solid bits of food
The biuret test for proteins
Equipment
- 2cm3 food sample Summary
- A test tube Prepare a food sample by breaking with pestle and
- A measuring cylinder The Benedict’s test for reducing sugars mortar. Transfer to beaker + distilled water. Stir. Filter
- 2cm3 Biuret solution Equipment solution with filter paper.
Method - 5cm3 Food sample
1. Add a few drops of Biuret’s reagent (sodium hydroxide and copper - A test tube Iodine test - starch - 5cm3 of food sample + few drops
(II) sulphate) to the food - 10 drops Benedict’s solution of iodine solution. Shake. Browny orange → blue black
sample in a test tube. - Hot water bath at 75°
2. Shake the solution to mix and wait for a few minutes. - Thermometer Benedict's test - reducing sugars - 5cm3 of food sample
3. If protein is present, the solution turns from blue to purple. - Pipettes + 10 drops of benedict’s solution - put into waterbath at
Method 75° for 10 mins. Blue → green/yellow/brick-red
1. Add a10 drops of Benedict’s solution to 5cm3 of your food
sample into a test tube. Biuret test - proteins - 2cm3 of food sample + 2cm3
2. Place in a hot water bath at 75°C for a 5 minutes. biuret solution. Shake. Blue → purple
3. If reducing sugar is present, the solution will change from
the normal blue to green, yellow or brick red - depending Emulsion test - lipids - 1cm3 food sample + 2cm3
on how much sugar is present. If reducing sugar is absent, ethanol + half test tube distilled water. White emulsion
the solution remains blue. formed at surface
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