Identifying Organic Compounds
BACKGROUND:
o Common foods, which often consist of plant materials or substances derived from animals, are
also combinations of these organic compounds.
o Simple chemical tests with substances called indicators can be conducted to determine the
presence of organic compounds.
o A color change of an indicator is usually a positive test for the presence of organic compound.
MATERIALS:
4 test tubes
wellplate
toothpicks
Q-tips
brown paper square
400 ml beaker
hot plate
test tube rack
goggles
Biuret solution
Benedict’s solution
Iodine solution
distilled water
dextrose solution
sucrose (table sugar) solution
olive oil
potato or corn starch solution
3 unknown samples
marking pen
SAFETY:
 Wear safety goggles for entire lab period.
 Use lab chemicals cautiously, they can irritate skin or stain of skin or clothing.
 Never touch or taste any chemicals.
 Use tongs or hot pads when handling heated materials.
PRELAB:
List the 4 groups of organic compounds found in living things.
PROCEDURES:
Test 1: Lipid Test
Negative (0) dried paper not translucent
Positive (+) dried paper translucent
1. Draw lines to make a 2X3 grid on a piece of brown paper.
2. Write the name of one test substance in each section (distilled water, olive oil, sample A, sample B,
sample C).
3. Use Q-tip to rub a small amount of each substance onto the brown paper until a “wet” spot
appears on the paper. Let paper dry for 15 mins.
4. Hold the piece of brown paper up to a bright light or window and look for a translucent spot on
the brown paper.
5. Record your results in data table
Test 2: Polysaccharide Test
Negative (0) yellow/gold
Positive (+)blue-black
1. Place well-plate on a piece of paper and label (distilled water, dextrose solution, starch solution,
sample A, sample B, sample C).
2. Place 4 drops of each substance in its labeled well. Add 3 drops of Lugol’s solution (iodine) to each
well. Also place a drop of iodine on the brown paper bag.
3. Stir each well with a clean toothpick.
4. Record the color of each well in data table.
Test 3: Monosaccharide Test
Negative (0) blue
Positive (+) blue-green; (++) green; (+++) yellow; (++++) brick red
1. Set up a hot water bath . Fill the beaker with 150 ml of water and turn the hot plate to its highest
setting. Both lab groups at the bench can share the water bath.
2. Label test tubes (distilled water, dextrose solution, starch solution, sample A, sample B, sample C).
Add 1ml (width of index finger) of solution to labeled test tube.
3. Add 5 drops of BENEDICT’S solution to each test tube.
4. When the water steams, place test tubes in water bath for 3-5 mins.
5. Use folded paper towel to remove test tubes from water bath and place them back in test tube rack.
6. Record results in data table.
7. Wash test tubes with soapy water and a test tube brush and set upside down to drain in rack.
Test 4: Protein Test
Negative (0) blue
Positive (+) pink - purple
1. Label 6 clean wells of the well-plate (distilled water, albumin solution, sample A, sample B, sample C).
2. Add 5 drops of each sample to its labeled well.
3. Add 4 drops of Buiret’s solution to each well. (Biuret reagent contains sodium hydroxide, a strong
base. If you splash any reagent on you immediately wash it off with water and notify the teacher)
3. Stir each well with a clean toothpick.
5. Record results in data table.
6. Wash well plate thoroughly with soapy water and a test tube brush.
6. Turn well-plate upside down on paper towel to dry and clean your lab bench.
DATA TABLE:
SAMPLE
water
olive oil
dextrose sol’n
starch sol’n
albumin sol’n
sample A
sample B
sample C
Lipid test
(brown paper)
Translucent
+/-
Monosaccharide Test
(Benedict’s)
Color?
+/-
Polysaccharide Test
(Iodine)
Color?
+/-
Protein Test
(Buiret’s)
Color?
+/-
ANALYSIS QUESTIONS: Use complete sentences!
1. Claim: Which substances contain lipids?
Evidence: What is your evidence of this?
Warrant: Warrant: Explain why this evidence supports the claim. Use the following sentence starter:
As a rule,
2. Claim: Which substances contain monosaccharides (simple sugars)?
Evidence: What is your evidence of this?
Warrant: Warrant: Explain why this evidence supports the claim. Use the following sentence starter:
As a rule,
3. Claim: Which substances contain polysaccharides (complex carbohydrates)?
Evidence: What is your evidence of this?
Warrant: Warrant: Explain why this evidence supports the claim. Use the following sentence starter:
As a rule,
4. Claim: Which substances contain proteins?
Evidence: What is your evidence of this?
Warrant: Warrant: Explain why this evidence supports the claim. Use the following sentence starter:
As a rule,
5. What is the purpose of using distilled water as one of the test substances?
6. What is the purpose of using substances that are known to contain the organic compound as
one of the test substances?
Critical Thinking:
7. Your brown lunch bag and it now has a large, translucent spot on the bottom. What explanation
could you give for this occurrence?
8. What conclusion could you make if a positive test result occurred for any of the organic
compounds in the test tube containing only distilled water?
9. Celiacs disease is a digestive disorder where a person cannot digest gluten, a protein found in
wheat. Which indicator would we use to test for gluten? How might this test be helpful to
a person with this disease?
10. Buiret’s solution will stain skin a purple-brown color. Explain why this happens.
11. The stomach contents of crime victims are often analyzed to provide information about
the victim’s activities before their death. Based on your results, predict which unknown
sample indicates a: A. fast-food meal, B. spaghetti dinner and C. peanut-butter and
jelly sandwich, with fruit and yoghurt. Explain your reasoning.
Lab Make-up assignment: do the lab simulation at this site, record your results and answer the questions
above.
http://www.okc.cc.ok.us/biologylabs/Documents/Organic%20Compounds/Organic%20Compounds.htm