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Biology-Glucose, Starch, Lipids and Protein Tests

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zoferume's version from 2017-05-30 18:57

Summary

This page helps you learn Glucose, Starch, Lipids and Protein Tests

Test For Glucose

Question Answer
Stage 1Place a small spatula measure of glucose in a test tube and add a little water.
Stage 2Then add several drops of Benedict’s Solution (contains alkaline copper sulphate).
Stage 3Add enough until the mixture is blue.
Stage 4Half fill a beaker with water and heat it on a tripod and gauze. Place the test tube in the beaker and allow the water to boil. (Using a beaker as a water bath is safer than heating the test tube directly)
Stage 5Continue to boil the water for a few seconds.
Stage 6The clear blue solution will change colour gradually forming a cloudy orange or ‘brick red’ precipitate of copper (I) oxide.
memorize

Test For Starch

Question Answer
Stage 1Place some starch powder in a spotting tile.
Stage 2Then add a couple of drops of dilute iodine solution.
Stage 3The iodine reacts with the starch which forms a ‘blue black’ colour.
memorize

Test For Lipids

Question Answer
Stage 1Use a pipette to place a drop of olive oil in the bottom of a test tube.
Stage 2 Add about 2cm of ethanol and shake to dissolve the oil.
Stage 3 Pour the mixture slowly into a test tube that is about three quarters full with cold water.
Stage 4 A white cloudy layer forms on the top of the water (The white layer is caused by the ethanol dissolving in the water and leaving the lipid behind as a suspension of tiny droplets called an emulsion.)
memorize

Test For Proteins (It is called the ‘biuret test’.)

Question Answer
Stage 1Add a little powdered egg white to 2 cm depth of water in a test tube.
Stage 2Shake to mix the powder with the water.
Stage 3Now add an equal volume of dilute (5%) potassium hydroxide solution and mix.
Stage 4Finally, add two drops of 1% copper sulphate solution. A mauve colour develops.
memorize