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
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
