Sec.
Name:
.
_
Experiment Tests For Presence of Organic
Nutrients (B. Science 10-2-3f)
Purpose: To determine whether sugar, starch, fat,
or protein molecules are present in a substance
by using chemical tests.
Materials: brown paper
Benedict's solution
Sudan '"
Biuret reagent corn syrup (clear)
vegetable oil1 % gelatin
1% starch
iodine solution
test tubes (lg. & sm)
test tube rack
10 ml graduated cylinder
'Methods: Wear Protective Eyeware
:1. Test for simple sugar. (Benedicts +
.
.
,",_",-,.-.- _-
-
---- simple sugar = red color)
R. I=>lace5 drops of water into one of the large test tubes.
b. Place 5 drops of corn syrup into the second large tt!st tube, starch into another tube,
gelatin into another tube, and vegetable oil into another tube.
c. Add 2 ml of Benedict's solution to each. Place in a boiling water bath for at least 5
minutes. Record the color of each tube, and if sugar was present.
2.. Test for starch (iodine + starch = blue. to black)
a. Place 5 drops of water into tube 1, (small test tube).
b. Place 5 drops of starch solution into the second small test tube, syrup into another
tube, gelatin into another tube, and vegetable oil into another tube.
c. Add 2 drops of iodine to each tube. Record color of each tube, and if starch was
present.
Test for fats and oits (oil dried - get translucent spots) or (oil + Sudan
lIil it will turn pink)
a. Spread 2 drops of vegetable oil on a piece of brown paper. On another section of
tt"fe brown paper spread 2 drops of water.
b. Hold the paper up to the light after it has dried some. Indicate which spot is
translucent.
3"
c. A more accurate test is to place about 1 cm of the substance to be tested in a dry
small test tube and add 10 drops of Sudan 11'- Set aside for 30 minutes. Record the
color of the tube after the 30 minutes, and indicate if fats were present. Do this test for
starch, syrup, gelatin, and vegetable oil.
4"
Test for proteins (Biuret + protein = pink or purple)
a. Place 2 drops of water into the first small test tube and 2 drops of gelatin (protein)
into tube 2. Add 2 drops of Biuret reagent to each tube. (CAUTION: USE CARE IN
HANDLING BIURET REAGENT. It may burn skin or clothing).
b. Observe & record the color that results. Indicate if proteins were present.
c. Repeat the test for starch, syrup, and vegetable oil.
Sec.
Results:
Carbohydrate Test
IBenedicts I Sugar II Iodine
Substance I Color
IPresent " Color
11
water
I
I
1% starch I
I
11
1% gelatin 1
I
11
syrup
I
I
11
veg. oil
I
1
11
Name:
.__.
_
Protein Test
Lipid Test
!!Sudan
I
Oil
"Biuret IProtein
I Starch
I Present "Color IPresent " Color IPresent
1
11__
'
II __
~I
_
1
1' __
'
11. __
-,1
_
--.01
_
1
11__
'
11__
1
11__
'
11
I
1
11__
'
11
1
Paper:
_
Conclusions:
1. What color does iodine turn when put on starch?
2. What is the positive test for oil using the brown paper test?
3. What is the color of the solution for a positive test for oil using Sudan III?
4_ What have you observed as being the positive test for starch?
5. What color change in Biuret reagent indicates the presence of protein?
6. What indicator reacts by turning from blue to brown or orange when heated with
certain sugars?
Discussion:
1. Which substance had a positive test for simple sugar in methods step one?
2_ What was the purpose of the first test tube (which was negative) in methods step 1?
3. What do we notice when the Biuret reagent reacts with protein?
4. What change occurs in the color of Sudan '" when it is in the presence of fat?
5. If an unknown sample was given to you and it caused Benedict's solution to turn
brick red, what organic compound was in this sample?
6. Your brown lunch bag has a large, translucent spot on the bottom. What
explanation could you give for this occurrence?
7. What conclusions could you make if a positive test for any of the organic
compounds occurred in the test tube containing only distilled water?
8. If you were given a solution of a unknown substance and you had to determine if it
was a sugar, starch, oil, or protein, how would you do this?
sugar
starch
oil
protein
9. We are studying the four major groups of organic chemicals that are needed in the
foods we eat. As we decide what to eat and as we eat what should we keep in mind
(Matthew 10:31 )?