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Category: Science and Technology
Date Submitted: 10/01/2014 03:48 PM
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...