Identifying Organic Compounds
Problem:
What are some of the major types of
organic compounds in common food products?
Background:
The most common organic compounds found in
living organisms are lipids, proteins, and carbohydrates. Common foods, which often consist of plant
materials or substances derived from animals, are also combinations of these
organic compounds. Substances called
indicators can be used to test for the presence of organic compounds. An indicator is a substance that changes
color in the presence of a particular compound.
In this lab, several indicators to test for the presence of lipids,
proteins, and carbohydrates (polysaccharides and monosaccharides) will be used.
Hypothesis:
If various indicators are used, then those
indicators will detect organic compounds in common food products.
Steps:
Be careful to avoid breakage when
working with glassware. Always use
special caution when using laboratory chemicals and equipment.
1. Gather all necessary materials for this
lab.
2. Place 8 test tubes in a test tube rack.
Each test tube is to be used for each of the
following experiments. Label the first 4 test tubes (1-4) and the
last 4 test tubes (A-D)
with a pencil only.
Note: (1) one “dropper full” is the same as one
squeeze of the bulb.
Testing for Lipids
1. Place a “dropper full” of Vegetable Oil
and (2) two “dropper fulls” of water
(from the
community table) into test tube #1.
2. Add 10 drops of
test tube.
3. Gently swirl the test tube for about 10
seconds.
4. The
orange/red at the top of the test tube and
the separation of that layer from the water are
also indicators that lipids are presence.
5. In the Data Table, record the indicator
used, what was observed (i.e. color,
characteristics, and/or changes), and the
type of organic molecule identified.
6. Place the test tube back into the test tube
rack. Don’t clean the test tube at this time
(unless told otherwise); the sample is to
be used as a control of the “unknown test”
latter in the lab; otherwise,
use the information recorded in your Data Table.
Testing for Proteins
1. Place a “dropper full” of the Gelatin
mixture into test tube #2.
2. Add 5 drops of Biuret Reagent to the test
tube. Be careful not to touch the
dropper to
the test tube.
3. Gently swirl the test tube for about 10
seconds.
4. The Biuret Reagent will change the solution
to a light purple or light blue-violet in the
presence of protein.
5. In the Data Table, record the indicator
used, what was observed (i.e. color,
characteristics, and/or changes), and the
type of organic molecule identified.
6. Place the test tube back into the test tube
rack. Don’t clean the test tube at this time
(unless told otherwise); the sample is to
be used as a control of the “unknown test”
latter in the lab; otherwise, use the
information recorded in your Data Table.
Testing for Carbohydrates: Polysaccharides
1. Place a “dropper full” of the Potato mixture into test tube #3.
2. Add 2 drops of Lugol’s Solution to the test tube. Be careful not to touch the dropper
to the test tube.
3. Gently swirl the test tube for about 10 seconds.
4. The Lugol’s Solution changes color from yellow-brown to a dark
blue/purple/green-
black in the presence of polysaccharides.
5. In the Data Table, record the indicator used, what was observed (i.e.
color,
characteristics, and/or changes), and the
type of organic molecule identified.
6. Place the test tube back into the test tube rack. Don’t clean the
test tube at this time
(unless told otherwise); the sample is to
be used as a control of the “unknown test”
latter in the lab; otherwise, use the
information recorded in your Data Table.
Testing for Carbohydrates: Monosaccharides
* Note: Hot water bath is
required for this lab and has already been set-up.
1. Place a “dropper full” of the Apple Juice mixture into test tube #4.
2. Add 10 drops of Benedict’s Solution to the test tube. Be careful not to touch the
dropper to the test tube.
3. Gently swirl the test tube for about 10 seconds.
4. Place the test tube into the hot water bath. Observe any color change for 2 minutes.
The Benedict’s solution will change color
from blue to green to yellow to orange to
possibly red in the presence of the
simple sugars, or monosaccharides as they are
being created from the break down of disaccharides
by the heat.
Carefully remove the test tube from the
hot water bath and place the tube in the test
tube rack.
5. In the Data Table, record the indicator used, what was observed (i.e.
color,
characteristics, and/or changes), and the
type of organic molecule identified.
6. Place the test tube back into the test tube rack. Don’t clean the
test tube at this time
(unless told otherwise); the sample is to
be used as a control of the “unknown test”
latter in the lab; otherwise, use the
information recorded in your Data Table.
Testing For an Unknown Substance:
1. Place a “dropper full” of the Unknown Substance in “each” test tube
labeled A-D.
The test tube labels will be for the
following: (A. lipids, B. proteins, and
C. polysaccharides, D. monosaccharides)
2. Repeat the tests described in the lab previously by following the
same directions for
each test tube (A-D). In other words,
test for lipids in test tube (A); test for proteins
in test tube (B); and test for
polysaccharides in test tube (C); and test for
monosaccharides in test tube (D).
3. Once a color change has occurred; compare it to your controls and/or
data chart to
see what the “unknown substance”
contained; lipids, proteins, polysaccharides, or
monosaccharides.
4. In the Data Table, record the final indicator that worked, what was
observed (i.e.
color, characteristics, and/or changes),
and the type of organic molecule identified.
5. In the Analysis section of the Data Sheet, complete the short answer
questions.
6. Clean and dry all necessary equipment including the table. Return all used materials
as directed.
