Download Activity 1: Determine the Presence of Organic Compounds

Activity 1: Testing for the Presence of Organic Compounds
Biochemists study the chemical composition of living things. They analyze the complex
chemical combinations and reactions involved in metabolism, reproduction, and growth.
Biochemists do most of their work in biotechnology, which involves understanding the complex
chemistry of life. These chemists may perform tests to identify organic compounds; compounds
that consist of carbon and hydrogen.
Carbohydrates, lipids, proteins and nucleic acids (DNA and RNA) are all organic
compounds. Each of these macromolecules plays an important role in your body. Carbohydrates
such as starches can be broken down into smaller units to give your body energy. Lipids such as
fat serve as long-term storage of energy and for cushioning vital organs while nucleic acids store
genetic material. Some proteins provide an organism’s structure while others digest
macromolecules.
Indicators are chemicals that change color when they react with a specific compound.
Benedict's solution is used to identify the presence of simple sugars and will turn yellowish
orange when heated. Lugol's iodine solution is used to identify the presence of starch and will
turn bluish black. Biuret solution is used to identify the presence of protein and will turn purple.
A brown paper bag can be used to observe the presence of fats. The paper will absorb the water
whereas oil cannot be absorbed and an oily spot will be evident.
In this lab you will test for the presence of organic compounds in various solutions. You
will test for starch, sugar, proteins and lipids. Before each experiment you must formulate a
hypothesis based on what you have learned about macromolecules and color change indicators.
Materials:
 6 test tubes per group
 Test tube rack
 Lab soaker or paper towels
 Brown paper bag cut into squares
 Benedict’s solution
 Lugol’s iodine
 Biuret solution
 Sharpie pens
 Gloves
 Lab coat or apron
 1 mL transfer pipettes
 Potato starch
 Gelatin
 Glucose solution
 Vegetable oil
 Parafilm wax paper
 Clock or timer
 Graduated cylinder
 Water bath with submerged test tube rack or beakers filled with water
Procedure:
1. Wear protective eyewear, gloves and apron or lab coat
2. Create a “placemat” with a lab soaker or paper towels
a. Keep all of your equipment and solutions on your mat
3. Using a Sharpie, label each test tube with your initials for identification
4. Label each tube appropriately for each experiment
a. Experiment 1: one tube labeled for starch one tube labeled water
b. Experiment 2: one tube labeled for glucose one tube labeled water
c. Experiment 3: one tube labeled for albumin one tube labeled for water
5. Place test tubes in a test tube holder
6. Mix appropriate indicator with solutions according to experiment
a. Experiment 1: add a few drops of iodine to each test tube
i. Place a small square of Para film wax over each test tube
ii. Mix gently
iii. Observe and record any color changes from the original color of the indicator
b. Experiment 2: using a transfer pipette, add 1mL Benedict’s solution to each tube
i. Heat at 100 Co for 2-3 minutes in a hot water bath
ii. Observe and record any color change from the original color of the indicator
c. Experiment 3: using a transfer pipette, add 1mL Biuret’s solution to each tube
i. Place a small square of Para film wax over each test tube
ii. Mix gently
iii. Observe an record any color change from the original color of the indicator
d. Experiment 4:
i. Label a piece of brown paper with your initials
ii. Draw 2 circles about the size of a quarter on your paper
iii. Put 2 drops of vegetable oil in one circle and 2 drops of water in the other
iv. Allow to dry at room temperature
v. If oil is present, it will leave a spot on the paper
vi. Observe and record your data
CLEAN UP
1. Using a sink, rinse out test tubes and put them back into test tube holders to dry
2. It is safe to throw the used transfer pipettes into the garbage
3. Throw away the brown paper, your gloves and your “placemat”
4. Put away your protective wear
NAME _______________________________
DATE ___________________
DATA TABLES
EXPERIMENT 1: TEST FOR STARCH WITH IODINE
HYPOTHESIS
______________________________________________________________________________
_____________________________________________________________________________
Tube
1
2
Indicator
A few drops of
Iodine
A few drops of
Iodine
Solution
1mL starch
1mL water
Treatment
Color
Change?
Starch Present?
Add a few
drops of
Lugol’s iodine
and observe
EXPERIMENT 2: TEST FOR SUGAR WITH BENEDICT’S SOLUTION
HYPOTHESIS
______________________________________________________________________________
_____________________________________________________________________________
Tube
1
Indicator
1mL Benedict’s
Solution
1mL glucose
2
1mL Benedict’s
1mL water
Treatment
Mix and heat test
tubes for 2 minutes
in a 100oC water
bath and observe
Color
Change?
Sugar
Present?
EXPERIMENT 3: TEST FOR PROTEINS WITH BIURET’S REAGENT
HYPOTHESIS
______________________________________________________________________________
_____________________________________________________________________________
Tube
1
Indicator
1mL Biuret’s
Solution
1mL gelatin
2
1mL Biuret’s
1mL water
Treatment
Color
Change?
Protein Present?
Mix and
observe
EXPERIMENT 4: TEST FOR LIPIDS WITH BROWN PAPER
HYPOTHESIS
______________________________________________________________________________
_____________________________________________________________________________
Solution
2 Drops oil
2 Drops of Water
Treatment
Allow circles to dry and observe
Fat Present?
Analysis Questions
1. What did the color changes indicate for experiments 1 through 3? Explain.
1.
2.
3.
2. How do you know that fat was present using the brown paper test? Explain.
3. Was your hypothesis accepted or refuted for experiment one? Use your data to explain.
4. Was your hypothesis accepted or refuted for experiment two? Use your data to explain.
5. Was your hypothesis accepted or refuted for experiment three? Use your data to explain.
6. Was your hypothesis accepted or refuted for experiment four? Use your data to explain.
7. Identify the controls in each experiment:
1.)
2.)
3.)
4.)