NAME: ____________________PERIOD:_____DATE:_______
Lab: Identifying Organic Compounds
Introduction:
The most common organic compounds found in living organisms are lipids,
carbohydrates, proteins, and nucleic acids. Common foods which often consist of plant
materials or substances derived from animals are also combinations of these organic
compounds. Simple chemical tests with substances called indicators can be conducted
to determine the presence of organic compounds. A color change of an indicator is
usually a positive test for the presence of an organic compound. In this lab, you will use
several indicators to test for the presence of lipids, carbohydrates (sugars and
starches), and proteins in particular foods.
Problem:
 How can you determine what types of organic compounds are found in some
common foods?
Pre-Lab-Discussion:
1. What are the four organic compounds that could be in food?
2. What is an indicator?
3. How is an indicator used to test for the presence of organic compounds in this
experiment?
4. What is the purpose of using distilled water as one of your test substances?
5. What is the purpose of washing the test tubes thoroughly?
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Materials:
 6 Test Tubes (pre-labeled)
 Test-Tube Rack
 Test-Tube Holder
 Hot Plate
 20ml Egg White and Water Mixture
 20ml Gelatin and Water Mixture
 20ml Melted Butter
 20ml Potato and Water Mixture
 20ml Apple Juice and Water Mixture
 20ml Distilled Water
 600ml Beaker
 Graduated Cylinder
 Iodine Solution
 Sudan III Stain
 Biuret Reagent
 Benedict’s Solution
Procedure:
Part A: Testing for Lipids
1. Make sure you have 6 test tubes with correct labels on them. You should have one
test tube for each of the food substances listed in the materials list.
2. Fill each test tube with 5ml (6 squirts) of the substance indicated on the masking
tape label.
3. Add 5 drops of Sudan III stain to each test tube. Sudan III stain is red and will form
a dark red layer at the top in the presence of lipids.
4. Gently shake the contents of each test tube. In the data table record any color
changes and place a check mark next to those substances testing positive for lipids.
5. Wash the test tubes thoroughly.
Part B: Testing for Carbohydrates
Sugars and starches are two common types of carbohydrates you will test for.
Starch Test
1. Refill each clean test tube with 5ml of the substance indicated on the masking tape
label.
2. Add 5 drops of iodine solution to each test tube. Iodine will change color from
yellow-brown to blue-black in the presence of starch.
3. Gently shake the contents of each test tube. In the data table, record any color
changes and place a check mark next to those substances testing positive for
starch.
4. Wash the test tubes thoroughly.
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Sugar Test
5. First set up a hot water bath by filling the beaker half full with tap water. Heat the
beaker of water on the hot plate. Bring the water to a gentle boil.
6. While the water bath is heating, fill each clean test tube with 5ml of the substance
indicated on the masking tape label.
7. Add 10 drops of Benedict’s solution to each test tube. When heated, Benedict’s
solution will change from blue to green, yellow, orange, or red in the presence of a
simple sugar, or monosaccharide.
8. Gently shake the contents of each test tube.
9. Place the test tubes in the hot water bath. Heat the test tubes for 3 to 5 minutes.
With the test tube holder, remove the test tubes from the hot water bath and place
them back in the test tube rack. In the data table record any color changes and
place a check mark next to any substances that test positive for a simple sugar.
10. After they have cooled, wash the test tubes thoroughly.
Part C: Testing for Proteins
1. Refill each clean test tube with 5 ml of the substance indicated on the masking tape
label.
2. Add 5 drops of biuret reagent to each test tube. Biuret reagent changes color from
blue to violet in the presence of protein.
3. Gently shake the contents of each test tube. In the data table, record any changes
in color and place a check mark next to any substances that test positive for protein.
4. Wash test tubes thoroughly.
Data and Observations:
Lipid Test
Carbohydrate Test
Protein Test
Substance
Sudan
Color
Lipids
Present

Iodine
Color
Starches Benedict
Present
Color

Egg White
Gelatin
Butter
Potato
Apple
Juice
Distilled
Water
3
Sugars
Present

Biuret
Color
Proteins
Present

Analysis:
1. Which test substances contain lipids?
2. Which test substances contain starch?
3. Which test substances contain simple sugars?
4. Which test substances contain proteins?
5. Which test substances did not test positive for any of the organic compounds?
6. Would you describe the tests that were performed in this experiment as being
qualitative or quantitative? Why?
7. People with diabetes are instructed to avoid foods that are rich in carbohydrates.
How could your observations in this experiment help you decide whether a food
should be served to a person with diabetes?
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8. What conclusion could you make if a positive test for any of the organic compounds
occurred in the test tube containing only distilled water?
9. A very thin slice is removed from a peanut and treated with Sudan III stain. Then a
drop of Biuret reagent is added to the peanut slice. When you examine the peanut
slice under a microscope, patches of red and blue-violet are visible. What
conclusions can you draw from your examination?
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