Download Testing for Organic Molecules Lab Lab #___

Name: __________________________________
Period: _____
Date: _______________
Testing for Organic Molecules Lab
Lab #___
Background:
Organic macromolecules are the large, molecular compounds, which contain carbon and hydrogen. Frequently, they also
contain oxygen and nitrogen. These compounds are essential to life for a variety of reasons. There are four main classes of
organic molecules, each with specialized roles to play within an organism.
Nucleic acids store and transmit hereditary information. Nucleic acids are chains of smaller, repeating units called
nucleotides. Carbohydrates are an essential energy source for living things. Simple sugars, or monosaccharides, are used for
immediate energy. Complex carbohydrates, or polysaccharides like starch, consist of chains of monosaccharides. These
macromolecules are used for longer-term energy storage, or for structural purposes. Similarly, lipids, typically consisting of a
glycerol molecule and fatty acids, are also used for energy storage and structural purposes. Proteins have an extremely diverse
range of functions. They consist of chains of amino acids and depending on their specific structure, can act as enzymes or
hormones and are essential to the growth and repair of cell.
Despite having many of the same elements in common, the different types of organic compounds are each structured
differently. This means that they will interact with chemicals in different ways and so we are able to use indicators to test for
the presence of these different types of organic compounds.
Materials:
Chemical reagents in dropper bottles
1. Lugols Solution (Iodine)
2. Biuret Solution
Foods to Be Tested
1.
2.
3.
4.
Bread
Butter
Egg Whites
Lemon Juice
1.
2.
3.
4.
5.
6.
7.
Other Materials
1 Test tubes with rack
Small beaker
Dropper
1 Q-tip
1 Brown Paper
2 Petri dishes
Blue Litmus paper
Pre Lab Questions: You will find the answers to these questions in the background information
1. Name the 4 macromolecules
2. What are the 2 major elements that make up organic compounds?
3. Why do organic compounds interact differently with certain chemicals?
4. Why do we use indicators?
Hypotheses:
5. Which food(s) do you think contain high amounts of carbohydrates?
6. Which food(s) do you think contain high amounts of proteins?
7. Which food(s) do you think contain high amounts of lipids?
8. Which food(s) do you think helps metabolize nucleic acids?
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Pre-Procedure:
How do each of the following indicators and materials work?

Lugol’s Solution (Iodine):

Biuret Solution:

Litmus Paper:

Brown Paper Bag:
Procedure: Place a CHECK MARK after you have completed each step
Test #1 - Test for the Presence of Starches (Carbohydrate)
1. ______ Place about an inch of bread into a small Petri dish.
2. _______Add two or three drops of Lugol's solution onto the center of the bread.
3. ______ Check for any color change. A positive test for carbohydrates is indicated if the bread turns blue-black in color.
4. _______ Write your results in row 1 in the data table on page 3
Test #2 - Test for the Presence of Lipid
1.
2.
3.
______ On a piece of brown paper, rub butter over its surface using a Q-tip
______ Hold the paper up to the light and observe. A positive test for fat is indicated if a translucent (see through)
spot is left on the paper. (Translucent spots do not dry).
______ Write your results in row 2 in the data table on page 3.
Test #3 - Test for the Presence of Protein
1.
2.
3.
4.
______ Add egg whites to a test tube using a dropper
______ Add about ten drops of Biuret solution to the test tube with the egg whites in it.
______ Shake the tube side to side carefully and observe. A positive test for protein is indicated by a change in
the color of Biuret from blue to pink or purple.
______ Write your results in row 3 in the data table on page 3.
Test # 4 for the Presence of Vitamin C (Ascorbic Acid)
5.
6.
7.
8.
______ Lay a piece of litmus paper in a petri dish
______ Carefully add one drop of lemon juice to one end of the pH paper
______ Observe if there is any color change. A positive test for acid will turn the blue paper red.
______ Write your results in row 4 in the data table on page 3.
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Data Table:
Color
Change?
Food
Tested
Nutrient Tested For
Solution or
Item Used
(Yes or no)
1. Conclusion (Was the nutrient present?)
Record Yes or No
2. Record your observations from the test to
support your conclusion.
1. ________________
1. Bread
2. ________________________________________
__________________________________________
__________________________________________
1. ________________
2. Butter
2. ________________________________________
__________________________________________
__________________________________________
1. ________________
3. Egg
White
2. ________________________________________
__________________________________________
__________________________________________
1. ________________
4. Lemon
Juice
2. ________________________________________
__________________________________________
__________________________________________
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Analysis Questions: You do not have to rephrase the question – however, be thorough and specific in your answers!
1. What is the difference between monosaccharides and polysaccharides? Give an example of each
2. There are large quantities of polysaccharides (starch) in potatoes. If you added several drops of Lugol’s solution on a
potato, predict which color the potato would turn. Use evidence (your observations) from test #1 to support your answer.
3. If you pour oil (fat) onto a brown paper bag, what will your results look like? Use evidence (your observations) from test
#2 to support your answer.
4. Explain how you could test if a candy bar contains protein? (refer to test #3)
5. Research has proven that you need vitamin C to maintain a healthy metabolism. Adding lemon juice to your diet has
shown to help metabolize (break down) nucleic acids into nucleotides. Why is important that we maintain a healthy
metabolism and metabolize these nucleic acids into their building blocks?
6. How can the use of solution indicators help us understand the type of nutrients we consume in various foods? Use
evidence from the lab to support your response
7. Which of the foods from this lab would be beneficial in providing long term energy storage?
8. Which of the foods from this lab should be consumed in order to maintain cell structure?
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