July 27, 2005

Test for Sugar

A sugar is a compound of carbon, hydrogen, and oxygen. It belongs to the group of nutrients called carbohydrates. Sugars taste sweet and are a source of energy for your body. Some sugars have to ability to give up 2 electrons. Copper ions eagerly accept 2 electrons, and when they do, they lose their ionized state and become copper metal—a great thing for chemists because there is a dramatic color change. Copper ions are blue, and copper metal is red. So if a color change from blue to red occurs, because the sugar gives up electrons to the copper, a chemist can tell that the sugar is present.

Disappointingly, one sugar that does not reduce copper ions to copper metal is ordinary table sugar, sucrose. But you can use the simple sugars found in fruits and honey for this test.

Here are two ways you can do the test. You can make up your own test solution, or you can use Fantastik cleaning solution. The test solution must contain copper ions in an alkali solution.

Materials and Equipment

• Fantastik or if you plan to make your own solution, you will need: copper scrubbing pad or copper pennies, a jar with a lid, ammonia, washing soda and measuring spoons
• heat-resistant custard cups
• pot holders or tongs
• food samples such as: honey or syrup, soda cracker, lemon, grapefruit, apple, banana, grapes, jellies, breads, cakes, etc.

Procedure

Before you do this test, CHECK WITH AN ADULT, AS YOU'LL BE USING THE STOVE.

You can use Fantastik as your test solution or make your own solution. The color change is much more dramatic in homemade test solution. To make your own test solution, put the copper scrubbing pad or 4 or 5 pennies in a jar containing about 1/4 cup of ammonia. Put the lid on the jar and let it stand overnight or until the solution is dark blue.

When the solution is ready, bring a cup of water to a boil, then remove it from the heat. Add a teaspoon of washing soda to the water. When the washing soda solution is cool, add 2 tablespoons of the ammonia-copper solution to it and mix. This is your alkaline copper-ion testing solution for sugar. Save the ammonia-copper mixture to make more test solution in the future. Keep the jar tightly closed.

If you use Fantastik, pour enough in a custard cup so that you can see its light blue color.

Put about 1/4 teaspoon of syrup or honey into the Fantastik or into approximately 2 tablespoons of your homemade test solution. Heat the mixture until it comes to a boil and then let it boil for a few seconds. Then remove from the heat. The Fantastik will turn a reddish yellow and the homemade solution will turn dark red: These are positive tests for sugar. Look for this color change when you test unknowns.

Repeat the procedure with a small sample of another food you want to test in a fresh batch of test solution. Make sure the solution boils briefly. Look for the color change that is a positive test for sugar.

WARNING: DO NOT EAT ANY OF THESE EXPERIMENTS.

Observations and Suggestions

There is an enzyme in your saliva that changes starch to sugar. See for yourself. Test a fresh piece of soda cracker for sugar in a test solution. You should have a negative test. Chew another soda cracker. Hold it n your mouth for five minutes, mixing it well with saliva. Test a small sample of chewed cracker for sugar. You should now get a positive result.

Reprinted with permission from Chemically Active! Experiments You Can Do at Home by Vicki Cobb. Text © 1985 by Vicki Cobb (www.vickicobb.com). Published by HarperTrophy.

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