Name: _______________________________________
Date: ___________ Period: _________
LAB: TESTING FOR ORGANIC COMPOUNDS (CP 2010)
PROBLEM: How can we tell which macromolecules are in a food?
BACKGROUND:
All living things require energy and raw materials for life functions and to maintain
homeostasis. Plants are able to make their own food from substances in the environment, but
heterotrophs get all their raw materials in the foods they eat.
Substances in food that can be used by an organism for energy or for growth and repair are
called nutrients. Nutrients include carbohydrates, proteins, fats, minerals and vitamins. The
nutrients that you will study in this lab make up your body cells. Thus, YOU ARE WHAT YOU
EAT!! In this activity, you will use indicator solutions to test for the presence of carbohydrates (starch
and sugar), protein, and lipids. A specific change in the color or the indicator identifies the presence of
a specific organic compound found in foods.
We will use these indicators:
1. Benedict’s Solution tests for simple sugars (monosaccharides / disaccharides)
2. Lugol’s Iodine Solution tests for starch (a polysaccharide)
3. Biuret’s Solution tests for protein
4. Brown Paper Bag tests for lipids
Since most of the samples are diluted in water, we must make sure that water alone does not change
the indicator color. The reaction between the indicator solution plus water will serve as the control
against which to compare other reactions.
OBJECTIVE: Students will be able to:
1. observe color change of chemical indicators on food molecules of sugar, starch, fat, and protein
2. identify the nutrients present in unknown food samples
MATERIALS:
3 nutrient indicators (Benedict’s, Lugol’s, Biuret’s)
variety of food samples & unknowns
distilled water
glucose solution
hot water bath
test tubes and rack
well plate
starch mixture
toothpicks
test tube holder
protein mixture
brown paper bags
PROCEDURE:
Part A: Observing Indicators on Known Nutrients: In order to tell if a food has a particular
nutrient in it, we must first determine how each indicator works. A positive test usually results in a
color change for a specific nutrient. To do this, add the chemical indicators to foods of known
molecules to see how they react.
Test for Carbohydrates:
Test for simple sugars in _________________________:
1. Obtain 2 clean test tubes. Label one “water” and one “sugar sln.” Place 20 drops of water in
one and 20 drops of sugar solution in the other.
2. Place 2-5 drops of Benedicts Solution in each test tube.
3. Place both test tubes in a hot water bath for 3 minutes. Observe the contents of each tube for color
change. Record your results in the data table.
Test for Starch, a polysaccharide in ____________________________________:
1. Obtain a well plate. Place 10 drops of distilled water in one well and 10 drops of starch solution in
another well.
2. Add 2 drops of Lugol’s iodine solution to each well. Record the color change that results in the
data table.
Test for Protein in _________________________:
1. Place 10 drops of water in one well of your test plate. Place 10 drops of protein mixture provided in
another well.
2. Add 2 drops of Biuret Solution to each well. Record any color changes in the data table.
Test for Fat ______________________________:
1. Place 1 drop of vegetable oil on a square brown paper and label “oil”. Place a drop of water on the
same piece of paper and label “water”.
2. Set the paper aside until the water evaporates.
3. When the water evaporates observe the brown paper and record any differences in appearance in the
data table.
Part B: Testing for Unknown Nutrients
1. Place 20 drops of Unknown Solution #1 in 4 different test tubes. Test the solution for the presence
of simple sugars, starchs, proteins, and lipids. Each test tube should be put through a different test.
2. Record your results in Data Table 2a.
3. Repeat Steps 1 and 2 for Unknown Solution #2 and record your results in Data Table 2b.
Name: ______________________________________________ Date: _____________________
DATA SHEET: Testing for Organic Compounds in Food
TITLE: ___________________________________________________________________________
PURPOSE (see objectives): The purpose of this lab is to ____________________________________
__________________________________________________________________________________
MATERIALS:
The following materials were used during this lab____________________________
__________________________________________________________________________________
__________________________________________________________________________________
PROCEDURE (summarize what you are expected to do in a list – DO NOT COPY):
Part A: Simple sugars: _____________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
Starch: __________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
Protein: __________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
Lipid: ___________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
Part B: ___________________________________________________________________________
__________________________________________________________________________________
_________________________________________________________________________________
RESULTS:
Substance
tested
Table 1: Indicator Response to Known Nutrients
Type of
Indicator or
Negative Test
Positive Test
Molecule
Test
(using water as a (color change of indicator)
control)
Simple Sugar
Benedict’s
Solution
Polysaccharide
Lugol’s Iodine
Solution
Protein
Biuret’s Solution
Lipid
Unknown # 1
Paper Bag Test
Table 2a: Testing for Unknown Nutrients
Indicator or Test
Color change of
Meaning of color change
indicator
Benedict’s Solution
Lugol’s Iodine Solution
Biuret’s Solution
Paper Bag Test
Unknown # 2
Table 2b: Testing for Unknown Nutrients
Indicator or Test
Color change of
Meaning of color change
indicator
Benedict’s Solution
Lugol’s Iodine Solution
Biuret’s Solution
Paper Bag Test
ANALYSIS QUESTIONS:
1. What is an indicator? _____________________________________________________________
__________________________________________________________________________________
2. Why was water used as a control to test each indicator? __________________________________
__________________________________________________________________________________
3. Name the indicator or testing material used to detect the presence of the following nutrients:
a. simple sugars: ____________________________________________________________
b. protein: __________________________________________________________________
c. starch: ___________________________________________________________________
d. fats: _____________________________________________________________________
4a. Benedict’s solution turns from __________________________ to _______________________ in
the presence of sugar after heating.
b. Iodine solution turns from __________________________ to __________________________ in
the presence of starch.
c. Biuret solution turns from __________________________ to __________________________in the
presence of protein.
d. Paper turns from ____________________________ to __________________________ in the
presence of fat.
5. List each food you tested and the nutrients you found in each.
a. __________________________________________________________________________
b. __________________________________________________________________________
c. __________________________________________________________________________
d. __________________________________________________________________________
6. List the 2 unknown mixtures and the nutrients you found in them.
a. __________________________________________________________________________
b. __________________________________________________________________________
CONCLUSION:
The purpose of this lab was _________________________________________________________
__________________________________________________________________________________
After performing the tests in this lab, it was discovered that.. (explain your results and be specific).
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
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