Name____________________
USING INDICATORS TO TEST FOR ORGANIC
COMPOUNDS
Background: Organic compounds include carbohydrates, proteins, fats, and
vitamins. These organic compounds make up the nutrients of the foods we
eat. Carbohydrates include simple and complex sugars and starches.
Gelatin is a form of concentrated protein and cooking oil contains lipids.
Ascorbic acid (also called vitamin C) and citric acid are additional nutrients
that our bodies need.
Objective: By the end of this exercise, you should be able to relate organic
compounds with their chemical indicator, and tell the positive and negative
test results for carbohydrates, proteins, fats, and vitamins.
Directions: Each member of the lab group needs to record the results of
each test in his notebook, and what each test tells him about the presence or
absence of the chemicals being tested. Answer all questions from this handout in your notebook. Be sure to echo the question.
SAFETY GOGGLES MUST BE WARN AT ALL TIMES IN THE LAB AREA
I.
TEST FOR STARCH
(a type of complex carbohydrate called a polysaccharide)


Clean out test tubes and number 6 test tubes in a test tube rack.
To the numbered wells, add the following...
#1
1 ml of glucose (monosaccharide)
#2
#3
#4
#5
#6
1 ml of sucrose (disaccharide)
1 ml of starch
(polysaccharide)
1 ml of distilled water
1 ml of gelatin (protein solution)
1 ml of cooking oil (fat solution)
N.B: 1 ml = 20 drops


Record the color of each solution before adding the indicator.
Add 5 drops of iodine solution to each test tube and record the color.
Data Table: Results of Starch (iodine) test
Test tube #1
(glucose)
Test tube #2
(sucrose)
Test tube #3
(starch)
Test tube #4
(water)
Test tube #5
(gelatin)
Test tube #6
(oil)
Color
before
Color
after
indicator
Questions:
1. If you were testing an unknown solution for starch, how would you know
whether starch is present or not?
2. What indicator do you use to test for the presence of starch?
3. What is the reason for well #4?
II.
TEST #1 FOR GLUCOSE
(a type of carbohydrate that is a simple sugar – monosaccharide)






Number 6 test tubes.
To the numbered test tubes add...
#1
1 ml of glucose (monosaccharide)
#2
#3
#4
#5
#6
1 ml of sucrose (disaccharide)
1 ml of starch
(polysaccharide)
1 ml of distilled water
1 ml of gelatin (protein solution)
1 ml of cooking oil (fat solution)
Add 1 ml of Benedict’s Solution to each well.
Record the color in each test tube.
Place the test tubes in a hot water bath. This is a beaker filled with hot water. For this
experiment, the hot water will speed up any reactions. Do not over heat, as this may
give you a false positive.
Record the colors after heating.
Data Table: Results of Monosaccharide (Benedict’s) test
Test tube #1
(glucose)
Test tube #2
(sucrose)
Test tube #3
(starch)
Test tube #4
(water)
Test tube #5
(gelatin)
Test tube #6
(oil)
Color
before
Color
after
indicator
Questions:
4. What color change tells you that a simple sugar (monosaccharide) is present?
5. Why do you need to heat the mixture?
III. TEST #2 FOR GLUCOSE
(a type of carbohydrate that is a simple sugar – monosaccharide)




On a spot plate, number wells #1 – 6.
To the numbered wells, add the following...
#1
1 ml of glucose (monosaccharide)
#2
#3
#4
#5
#6
1 ml of sucrose (disaccharide)
1 ml of starch
(polysaccharide)
1 ml of distilled water
1 ml of gelatin (protein solution)
1 ml of cooking oil (fat solution)
Take a small piece of Tes-tape and dip it into each one of the solutions.
Record the color of the tape and use the color chart on the package to interpret the
results. Record these findings.
Data Table: Results of Monosaccharide (TesTape) test
Well #1
(glucose)
Well #2
(sucrose)
Well #3
(starch)
Well #4
(water)
Well #5
(gelatin)
Well #6 (oil)
Color
before
Color
after
indicator
Questions:
6. What color indicates a positive result for the presence of glucose
(monosaccharide)?
7. What results of the above two monosaccharide tests could indicate the presence
of disaccharide?
8. Explain a method of a possible test for the presence of disaccharide?
IV.


GELATIN TEST (a concentrated protein solution)
Clean out your test tubes or wells.
To the numbered test tube or wells, add the following...



#1
1 ml of glucose (monosaccharide)
#2
#3
#4
#5
#6
1 ml of sucrose (disaccharide)
1 ml of starch
(polysaccharide)
1 ml of distilled water
1 ml of gelatin (protein solution)
1 ml of cooking oil (fat solution)
Record the initial color of each well.
Add 5 drops of Biuret reagent to each well.
Record the color of each well in your.
Data Table: Results of Protein (Biuret) test
Test tube #1
(glucose)
Test tube #2
(sucrose)
Test tube #3
(starch)
Test tube #4
(water)
Test tube #5
(gelatin)
Color
before
Color
after
indicator
Question:
9. What color indicates a positive result for the presence of protein?
10. Describe the protein solution.
Test tube #6
(oil)
V.


LIPIDS (FATS) TEST (cooking oil)
Clean out your test tubes or wells.
To the numbered test tube or wells, add the following...



#1
1 ml of glucose (monosaccharide)
#2
#3
#4
#5
#6
1 ml of sucrose (disaccharide)
1 ml of starch
(polysaccharide)
1 ml of distilled water
1 ml of gelatin (protein solution)
1 ml of cooking oil (fat solution)
Record the initial color of each well.
Add 5 drops of Sudan IV to each well.
Record the color of each well in your.
Data Table: Results of Lipids (Sudan IV) test
Test tube #1
(glucose)
Test tube #2
(sucrose)
Test tube #3
(starch)
Test tube #4
(water)
Test tube #5
(gelatin)
Test tube #6
(oil)
Color
before
Color
after
indicator
Questions:
11. What color indicates a positive result for the presence of lipids?
12. Describe the lipid liquid. Does it dissolve in water or remain separate?
CITRIC ACID & ASCORBIC ACID TESTS
VI.
You can run all trials and tests concurrently.
citric acid test

Into three wells, add in the following order...
1.
2.
3.
4.
10 drops of citric acid solution.
10 drops of manganese sulfate.
2 drops of potassium permanganate.
Record the color.
control

Into three wells, add in the following order…
1. Add 10 drops of water to a well.
2. Repeat steps #2 and #3 of the citric acid test.
3. Record the color.
ascorbic acid test
 Into three wells, add in the following order…
1. Add 10 drops of ascorbic acid to a well.
2. Repeat steps #2 and #3 of the citric acid test.
3. Record the color.
Data Table: Citric Acid & Ascorbic Acid Tests
Citric acid
Water (control)
Color Changes
test for both ascorbic acid and citric acid
Ascorbic Acid
1.
2.
3.
4.
5.
6.
Predict the color you expect to get in.
Add 10 drops of citric acid to a well.
Add 10 drops of ascorbic acid.
Repeat steps #2 and #3 of the citric acid test.
Record the color.
State a conclusion from this test.
Prediction:
Data Table:
Citric acid &
Ascorbic acid
Color Changes
Conclusion: