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Biology-Mr.Willets
Lab-Tests For Organic Compounds
There are a variety of chemical tests used to find out if certain organic compounds are present or not. Today, you will perform some of these tests. The first four parts show you how the tests work. Part five involves testing some foods. (NOTE- when you are asked to put about 1/2 inch of a liquid in a test tube, use the width of your pinky finger as being about that size)
Part 1- Benedict's Test for Monosaccharides
a) Place about one half inch of glucose solution (a monosaccharide) in a clean test tube.
b) Add five drops of Benedict's solution
c) Place the test tube in the hot water bath at the front desk.
d) Observe for several minutes and note any color changes that occur-
e) Clean out your test tube.
The original blue color was due to the Benedict's. What colors (in order) appeared as the sample was heated? _________________________________________________________________________
This will happen if Benedict's is added to a monosaccharide. What could we do to prove to ourselves that Benedict's solution will not change color without monosaccharide?______________________________ ____________________________________________________________________________
Part 2- Iodine Test for Polysaccharides
a) Place about one half inch of starch (a polysaccharide) solution in a clean test tube.
b) Add one drop of iodine solution (iodine is brown although it may appear reddish in the bottle)
c) Note any color change that occurred.
What color change occurred? ______________________________________________________
This happens when iodine is added to a polysaccharide. To show that it won't happen with glucose, put some glucose solution in a clean test tube and add some iodine. Does it change to blue/black or remain brown?______ The color change to blue/black will only occur with a polysaccharide.
Part 3- Biuret Test for Proteins
a) Place about one half inch of protein solution in a test tube
b) Add five drops of Biuret A solution and five drops of Biuret B solution.
c) Swirl the test tube and observe.
What color appears in the test tube? __________________ This happens when Biuret is added to protein.
(sometimes, if the color is not obvious, a few more drops of each Biuret solution are needed- remember this when doing this test later on in this lab)
Part 4- Brown Paper Test for Fats
a) Take a piece of brown paper and rub a drop of oil on it using the Q-tip in the jar of oil.
b) Hold the paper up to the light to see the effect the oil has on the paper.
The oil has made the paper __________________________(do you know the right word?) This can be used to detect the presence of fats.
c) To prove that water will not have the same effect, repeat using water.
d) There are chemical tests for fats but we will not do any of those.
Part 5- Food Testing
There are 4 food products available at the side of the room. You should test as many as there is time for. For each food, test for monosaccharide (Benedict's Test), polysaccharide (iodine test) and protein (Biuret test). We won't do the fat tests. CLEAN ALL TEST TUBES BETWEEN TESTS!!!
A) Get a saltine cracker. Crumble about 1/3 of it into a clean test tube. Add a little water.
Crumble another 1/3 into another test tube and add a little water. Let both these test tubes sit for while you continue with this part. Take the remaining 1/3 cracker and place a drop of iodine on it. What color do you see? What does this tell you?
In one of the test tubes that has the cracker and water, place 5 drops of Benedicts and place the test tube in the hot water bath. After several minutes, does it change color? What does this tell you?
In the other test tube with cracker and water, put 5 drops of Biuret A and 5 drops of Biuret B. Does it change color? What does this tell you?
Record the results of these tests
B) Get a packet of Nutra-Sweet. Place 1/3 of it into each of three test tubes and add a little water to each.
Instead of packets, there might be a container of the powder. If so, put a scoop of Nutra-Sweet into each test tube and then add the water.
Add 5 drops of Benedicts to one and heat. Is there a color change? Add 5 drops Biuret A and 5 drops Biuret B to another. Is there a color change? Add 3 drops of iodine to the third. Is there a color change? In each case, what do the color changes (or lack of change) tell you? Record the results.
C) Put a dropper of egg white into each of three test tubes. No need to add any water. Run the tests for monosaccharides, polysaccharides and proteins. Record the results
D) Put a dropper of Gator-Ade into each of three test tubes and test them as before. No need to add water.
Record the results