Rev. 1/25/13
Team members:
Unknown # (from instructor) ---------------
Date:
Block:
Honors Biology – Chemical Analysis of Organic Groups
Introduction:
There are 4 main groups of organic molecules important to life.
Proteins, carbohydrates, lipids & nucleic acids. These groups can be
determined in unknown samples with chemical indicator
solutions…solutions that react with the unknown in an obvious &
predictable manner (usually by color change). Five simple tests exist
that can determine the presence of lipids, proteins, and two different
types of carbohydrate: glucose (a simple monosaccharide sugar) and
starch (a complex molecule made of simple sugars bound together &
used to store energy in plants).
These 5 diagnostic tests, including the reagents, procedures and their
reactions to specific molecule types are summarized in Table 1.
Table 1.
Reagents/Tests for Various Organic Molecules
Type of
Reagent
Type of
Molecule
Tested
Sudan II (III)
Lipid
Benedict’s
Solution
Glucose
(simple sugar)
Biuret’s
Solution
Protein
Iodine
Brown Bag
Test
Starch
Lipid
Instructions
Double sample
size by adding
water (Add 3
drops of
Sudan, shake &
let set for 5
minutes
Add 3 drops,
shake & heat
in hot water
bath for 10
minutes
Add 3 drops
Add 3 drops
Rub sample on
brown paper
Appearance
of Positive
Test
Red layer on
clear layer
Appearance
of Negative
Test
Uniform red
color
throughout
sample
Yellow, brick
red or green
color
Light blue
Changes to
purple
Light blue
Midnight blue
Dark shiny
spot,
somewhat
translucent
Yellowish
Spot dries to
normal
appearance of
paper
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Hypothesis:
If the behavior of indicator reagents are observed in samples of known
molecular types to which they react, then positive reactions with an
unknown sample can reveal the molecular type of that sample as well.
Materials:
1 test tube rack
12 test tubes
~6” tape
1 test tube clamp
4 organic reagents
1 scrap of brown paper towel
4 known aqueous samples (5-10 ml.) – lipid, starch, glucose, protein
1 unknown sample (~20 ml) - lipid, starch, glucose or protein
Procedure:
Part One—Identifying Positive Tests
Comparing positive reactions between reagents and the
macromolecules they are specific towards and the negative reactions
between these same reagents and water, a control (C), identifies the
appearance of a positive reaction for each reagent.
Label 8 test tubes – lipid, protein, glucose, starch, and lipid C, protein C,
glucose C & starch C.
Tear your brown paper into 2 pieces…label one lipid & the other lipid C
Place ~ ½ “ water in the C (control tubes) & test with each of the organic
reagents following the instructions presented in introduction. Test the
brown paper labeled lipid C with water. Set these aside for later
comparison with the positive tests.
Next, receive a sample of each of the known organic compounds in the
appropriately labeled test tubes. Twisting a paper towel into a swab,
apply a small spot of lipid onto the paper towel labeled lipid. Set this
aside for later comparison. Following the instructions provided in the
introduction, test each of the known samples with the appropriate
indicator solution.
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Compare the appearance of the positive tests, with the known samples,
to the negative tests with the controls. Make any necessary notes to
Table 1 to better describe the appearance of positive & negative tests.
Part Two—Identifying an Unknown Sample
Obtain a sample of an unknown organic compound from your
instructor. Write the unknown identifier # in the space provided on the
header of your teams lab handout. Next, divide the unknown sample in
approximately equal amounts between 4 clean test tubes. Also wet a
swab with the unknown and apply a small spot to a piece of brown
paper labeled unknown. Number the test tubes (1-4) & enter the
number on Table 2 in the row immediately below the reagent you will
use to test that sample. Note: it is critical that you are very
organized. Treat each test tube with the appropriate reagent (see
Table 1 for instructions). Compare your results for each test with the
examples of positive & negative (water control) tests described in Table
1. Record the results (positive or negative) for each of the 4 indicator
solutions & the brown paper. Using that data, record the type of
molecule (lipid, sugar, protein or starch) found in your unknown sample
in your conclusion.
Data:
Table 2.
Results of an Unknown Sample
Sudan
III
Test Tube Number
Benedict’s
Biuret’s
Iodine
Brown
Paper
Not
applicable
Test Result (+ or -)
Conclusion:
Based on the test results, the unknown sample is a___________________.
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