CARBOHYDRATES - HOW SWEET THEY ARE! J

There are two biochemical tests used to test for the presence of specific groups of carbohydrates – the Benedict’s test and the Iodine test. The following table shows the reaction patterns for the three groups of carbohydrates:

Benedict’s Test / Iodine Test / Carbohydrate Type
+ / - / Monosaccharide
- / - / Disaccharide
- / + / Polysaccharide

Test Results:

A positive Benedict’s test will look / An orange color
A positive Iodine test will look / A purplish black color

In this lab you will perform these tests to identify the food source for four unknowns.

Materials:

water bath water

Benedict's solution Unknowns A, B, C

Iodine solution test tubes

marker test tube rack

*You must wear safety goggles and apron at all times!*

Procedure:

Benedict’s Test:

1. Label five test tubes with your group number - A, B, C and control.

2. Add 16 drops of Unknown A to test tube A.

3. Add 16 drops of Unknown B to test tube B.

4. Add 16 drops of Unknown C to test tube C.

5. Add 16 drops of water to the tube labeled “control”.

6. Add 8 drops of Benedict's solution to each of the five test tubes.

7. Carry the test tube rack to a water bath and place all five test tubes in the rack in the hot water bath for 4 minutes.

8. Carefully remove your tubes, place them in your test tube rack, and return to your station.

9. Record your results in the Data Table. An orange color indicates a positive reaction.

10. Discard solutions in sink. Thoroughly rinse the test tubes after.

Iodine Test:

1. Label five test tubes with your group number - A, B, C and control.

2. Add 16 drops of Unknown A to test tube A.

3. Add 16 drops of Unknown B to test tube B.

4. Add 16 drops of Unknown C to test tube C.

5. Add 16 drops of water to the tube labeled “control”.

6. Add 4 drops of iodine solution to each test tube. Do not heat the iodine solution!

7. Swirl the test tubes gently. A purplish black color is a positive reaction. Record in the Data Table.

8. Discard solutions in sink. Thoroughly rinse the test tubes after.

When both tests are completed, wipe down the tabletop with cleaner and paper towel. Remove safety equipment. Use your test results, the table below, and your knowledge of carbohydrates to identify each unknown solution.

Carbohydrate Content in Foods
Food / % Carbohydrates
Rice / 79.9% starch
Maple syrup / 77.0% sucrose
Honey / 82.3% glucose

***Hint: is starch a monosaccharide, disaccharide or polysaccharide?

***Hint: is sucrose a monosaccharide, disaccharide or polysaccharide?

***Hint: is glucose a monosaccharide, disaccharide or polysaccharide?