Testing for Macromolecules

SBI3U1 Testing for Macromolecules

All living organisms are composed of various types of organic molecules, such as carbohydrates, starches, proteins, lipids, and nucleic acids. These substances, contained in the foods we eat, provide us with the energy and cellular building blocks necessary for life. Several of these molecules can be detected by simple chemical test.

Begin by performing the following tests on known foods to observe a positive result. It is recommended that you then repeat each test with sodium bicarbonate to observe a negative result. These observations will be helpful when you go on to test foods of unknown composition.

Materials:

Iodine

Benedict’s reagent

Biuret reagent

Ethanol

Test tubes and racks

Spot plates

Hot plate

Beakers

Stirring rods

Scoopulas

Unknown food samples

Cooking oil

Glucose solution

Starch powder

Gelatin solution

Sodium hydrogen carbonate

Procedure:

1. Test for Starch

Place a little starch powder in a depression on a spot plate. Add a few drops of iodine. Repeat with sodium bicarbonate.

Positive result: blue/black colour

Negatvie result: brown colour

2. Test for Glucose

Benedict’s reagent contains blue Cu2+ ions that join with monosaccharides. The Cu2+ ions then change colour. Place equal amounts of a strong glucose solution and Benedict’s reagent in a test tube. Lower the test tube into a beaker of boiling water and wait for two minutes. Repeat with equal amounts of sodium bicarbonate and Benedict’s reagent.

Strong positive result: brick red precipitate

Medium positive result: yellow orange precipitate

Weak result: green colour

Negative result: blue colour

3. Test for Proteins

Add a little gelatin solution to a test tube. Add a few drops of Biuret reagent. Repeat with sodium bicarbonate.

Positive result: purple colour

Negative result: blue colour

4. Test for oil and fat

Place a little ethanol in a test tube. Add a few...