Monomer and Polymer Chemistry
This activity , a modification of a Frey Scientific activity, was designed to help students understand monomer/polymer chemistry of starches and sugars.
In today's environmentally conscious society we are always looking for new and better ways to conserve natural resources. Packing materials have in the past often consisted of pellets formed from a petroleum base
Today, many suppliers are using a starch based pellet that not only doesn't use petroleum, but can be easily broken down to reduce landfill volume. We will recycle these pellets in today's activity. We will use these pellets to form a starch solution.
Human saliva contains the enzyme amylase which aids in the breakdown of starches into sugars (which are smaller molecules). If you can place a piece of bread or cracker in your mouth, let your saliva react with it for a few seconds, the food should start to taste sweet. People produce an average of 1-1.5 liters of saliva every day.
METHODS OF MOLECULE IDENTIFICATION
Starch test solution is a combination of iodine and potassium iodide that turns dark blue to black when put in contact with starch. Use this test by adding a couple drops of the test solution to a small quantity of the sample to be tested. In general, the more starch present, the darker the color.
A Benedict's test for sugar involves adding a few drops of Benedict's solution to the suspect solution and heating gently (often in a boiling water bath). A positive sugar test will produce a brick-red color.
A Fehling's test for sugar involves the addition of Fehling's solution to the suspect solution and the heating of the mixture to near boiling. A red color (or yellow-green) indicates the presence of sugar.
- Make a starch solution by adding one starch packing pellet to 40 ml of water in a small beaker. Mix this well to get the pellet to dissolve completely. This is the starch solution you will use.
- Place approximately 10 ml of the starch solution in a paper dixie cup. Place 2-3 drops of the solution in a white depression plate. Add a drop of iodine to the depression well. Record results.
- Add 1 ml of saliva to the 10 ml starch solution and mix well. Record the time you add the saliva. Every 2 minutes remove 2-3 drops of the solution, place in a depression and immediately add a drop of iodine. Record the color of the solutions until you see significant changes (at least 10 minutes). Be sure to rinse your dropper between each test.
start color =
Time 2min 4min 6min 10 min 12min 14min
- Put 10 ml of starch solution in a test tube. Add 1-2 ml of vinegar. Put the test tube in a boiling water bath for 5 minutes. Test the solution for starch and sugar. If time allows, test a control for this procedure. Record your results.
QUESTIONS FOR STUDENTS:
- Why is it necessary to rinse your dropper between tests in PI?
- How could the amount of saliva used affect your results?
- What human system is simulated by the acid used in PII (vinegar=acid)?
- Explain the control you chose in Procedure II.