Download Title: Organic Molecules

Daiva Kuncaite
Bio 201
Prof. Wijesinghe
09/29/2009
Week II
Title: Organic Molecules
Objectives: carry out the experiment to determine if the substance is organic or inorganic. Use
various regents and methods to identify organic substances class. Identify organic compounds
found in the assigned unknown solution.
Introduction: The key factor that distinguishes organic substances from inorganic is the element
carbon. The main organic compound find in living organisms are protein, lipids, carbohydrates
and nucleic acids. Carbohydrates ratio of C:H:O is 1:2:1. They are polar molecules and soluble
in water. The simplest carbohydrates are monosaccharide (ex. Glucose). Two monosaccharide
forms disaccharides (ex. Sucrose, lactose) and more than two molecules of monosaccharide form
polysaccharide (ex. Starch). Lipids in their structure contains less O than in carbohydrates,
therefore lipids are nonpolar and water insoluble. Proteins are polymers of the amino acids.
Proteins have complex structure but also have a vast variety of functions.
Procedure: Since we carried many experiments I will explain each experiment procedure
individually. To determine if the substance is organic we took a small amount of each desired
substance in the test tube and using a Bunsen burner checked if the substance burned and
blackened. Each test tube we hold using test tube holder and away from the face in order to avoid
any damage. To carry on further experiments we had always prepare positive control and
negative control test tubes. The negative control always indicated that molecules we are looking
for are not presented. The positive control always indicates the presence of desired molecule. For
each experiment water served as negative control. However, positive control changed
accordingly to the experiment. To determine presence of reducing sugar, which is mainly
mosaccharides, we took each desired substance about 2 ml in the test tubes and added 2-3 drops
of Benedict’s reagent. Then we brought the water to boiling in the beaker on the heating plate.
Placed each test tube in the hot water bath for no longer than one minute and observed the
changes. The positive control was glucose solution. To determine the presence of starch we used
iodine reagent. We pour about 2 ml of each desired substance in the test tube and added one
drop of iodine in each. We observed the appearance of the blue-black color. The positive control
was starch solution. To determine the presence of fats we did test using Sudan IV reagent,
which stains the fats. We took about 5 ml of desired substance in the test tubes and added 5 drops
of the Sudan IV reagent, which stained the fats red. The positive control was vegetable oil. To
determine the presence of fats we also used Greasy Spot Test. On the white paper towel we lay
out the desired substances, crush them, and labeled them. After the substances dried we recorded
our observations. To determine the presence of proteins we used Biuret reagent. We took 2 ml
of the desired substances in the test tube and added 2-3 drops of Biuret reagent and recorded the
appearance of purple or lavender color which indicated the presence of protein. The positive
control was Albumin solution. The professor assigned the unknown solution # 2 to test for the
Daiva Kuncaite
Bio 201
Prof. Wijesinghe
09/29/2009
Week II
presence of any organic substance(s). We divided assigned solution in 4 test tubes. First test tube
we test for reducing sugar by adding few drops of Benedict’s reagent’s in the solution and
placing the test tube in the hot water bath. The second test tube we tested for starch by adding
few drops iodine. The third test tube we tested presence of protein by adding Biuret reagent. The
last test tube we test for lipids by adding few drops of Sudan IV reagent.
Results and Conclusions:
Determination if the substance is organic
Since gelatin, sugar and milk had burned and blackened we concluded that these three
substances are organic, whereas salt and chalk dust are inorganic compound and didn’t changed
color during the experiment.
Reducing Sugar
The negative control test tube with water after adding Benedict’s reagent turned sky blue and
remain the same after the hot bath, whereas the positive control test tube with the glucose
solution turned orange after the hot water bath. Therefore the color change to yellow/orange
indicated the presence of reducing sugar. The positive results appeared in milk, Apple juice,
dilute molasses, onion juice, lactose and sucrose solution. Sucrose solution supposed to give
negative results if we use pure sucrose. However, the industrial sucrose we used in the
experiment might have contained glucose contaminations which lead to the positive results of the
test. Since lactose gave positive result, milk also showed the positive results sign in yellowish
appearance, because it contains lactose as component. Therefore lactose is a reducing sugar.
Powder cracker in water and starch solution showed no presence of the reducing sugar as it was
expected.
Starch
The negative control test tube after adding iodine turned amber-brown color, which indicated no
presence of starch. The positive control test tube with starch solution had turned black-blue color
after adding iodine. In addition, we received positive results indicating the presence of starch in
paper, potato, and bread. However, paper contains cellulose, a different type of polysaccharide
then starch, therefore we got positive results.
Fat test using Sudan IV
The negative control test tube with water after adding reagent turned pink, evenly distributed
color. The positive control test tube was mixing water with oil and few drops of reagent, which
colored in red the fat layer on the surface of water. However, when we added the reagent in the
Daiva Kuncaite
Bio 201
Prof. Wijesinghe
09/29/2009
Week II
third test tube which contained water, oil and detergent we observed emulsification. The red
droplets of oil appeared instead of layer and the boundaries between oil and water diminished.
Greasy Spot Test
Water stain as negative control had dried without leaving oily stain on the paper towel. The
vegetable oil, a positive control had left an oily stain after drying. In addition potato chip and
peanuts gave positive results which indicated the presence of fats. Sucrose solution gave negative
result as it was expected.
Protein
The negative control test tube containing water gave a blue color after adding Biuret reagent. The
positive control test tube containing Albumin, which is a protein, after adding reagent, gave
purple color. Milk and crushed peanuts showed slightly purple color, which indicated that they
have some amount of protein present. However, sucrose solution, powdered cracker and
vegetable oil remained blue colored, which indicated no presence of the proteins.
Unknown #2
The test for starch and protein gave positive results, which lead us to the conclusion that the
unknown #2 contains two organic substances: starch and protein. Test for reducing sugar and
lipids gave negative results.
Homework:
1. What reagent do you use to test for a monosaccharide?
Benedict’s reagent.
2. Do all of the tests require heating? Which one do?
Not all tests require heating. Only test for reducing sugar using Benedict’s reagent and in
determination if the substance is organic.
3. What color is a positive test for protein?
Purple/lavender
4. Why does sucrose (table sugar) give a negative result for Benedict’s test?
Sucrose is non reducing sugar and doesn’t react with the Benedict’s reagent. However, the
industrial sucrose we used in the experiment might have contained glucose contaminations which
lead to the positive results of the test.
Daiva Kuncaite
Bio 201
Prof. Wijesinghe
09/29/2009
Week II
5. What are the monomers of proteins called?
Amino acids.
6. Most lipids fall into the category of triglycerides. What is the term for a triglyceride that
is a liquid at room temperature?
Unsaturated
A solid?
Saturated
7. What simple test can you run to tell if a substance is organic or not?
Burn the material. If the material burns and blackens the material is organic.
8. What element do all organic substances contain?
Carbon