Chemical Identification of Foodstuffs
Introduction: there will be a quiz on the procedures, purpose and warnings before you start the lab.

Purpose: Use chemical indicators to test for the presence of a simple carbohydrate, or complex
carbohydrates, or protein in an unknown solution. Special note: your unknown could contain a
simple sugar, starch, protein, all of them, just two of them, or none of them.

Hypothesis: does your u/k contain a sugar, starch or protein? Hint: use your senses, other than
your sense of taste and look at the known solutions at your lab table to help you form your
hypothesis.

Variables:
o Control- we have two: (2 pts)
o Manipulated (Independent)o Response (Dependent)- what are we recording in this lab?

Materials: list any warnings
Be sure to work at your assigned station because points will be taken off your lab if your lab
station is not cleaned up (even if you didn’t work there.)
Every station should have:
 One 250 or 400 ml
beaker
 Four test-tubes
 10 ml graduated cylinder
 Test-tube rack
Every lab table should have:
 a hot plate
 Benedict's solution (stains clothing)
 Iodine solution (stains clothing)
 Biuret's reagent (corrosive)
 Monosaccharide (corn syrup)
 1- plastic
pipette.
 a polysaccharide (starch)
 Protein (gelatin)
 Test-tube brush
 Sharpie pen
 Grey lab container for stations w/o H2O
Procedure: summarize all three parts in your own words so I know what you basically did to test for
sugars, starches and proteins.
Part 1: Test for Simple Sugars
1. Fill your beaker about 1/2 full of tap water and place it on the hot plate. Plug in hot plate and
turn it on to the highest setting. Allow the water to boil while you continue with the lab.
2. Clean and dry all your test tubes to ensure no left over contaminants from the previous period.
3. Mark one test tube unknown and ask your instructor to fill the tube 2/3 full with your assigned
unknown. Mark the tubes on the glass portion, near the top.
4. If you don't identify unknown at the top right corner of your lab write-up then you will
lose 10 pts-no exceptions! Place unknown tube in your test tube rack furthest away from the
other three test tubes and it should have it’s own pipette.
5. The remaining 3 test tubes should be marked as test tube #1, test tube #2, and test tube #3.
Mark the tubes on the glass portion, near the top.
6. Place ten drops of water into test tube #1, ten drops of corn syrup solution into test tube #2, and
ten drops of your assigned unknown in test tube #3.
 Be sure to always use a separate pipette for your unknown and answer question “a” in
your data analysis section of your write-up.
7. Using a graduated cylinder, add 3 ml of Benedict’s solution to all three tubes.
8. Carefully place all three test tubes in the boiling water bath for 3-5 minutes. When the color
stops changing in test tube 2 then you can turn off the heat.
9. Wait for test tubes to cool down and use your fingers to carefully remove the test tubes.
10. Compare your unknown in test tube #3 to test tubes 1 and 2, to determine whether or not your
unknown contains any simple sugars. Record your observed colors in the data table.
11. Answer questions b-e.
12. Let the water in the beaker cool down and carefully pour the hot water down the drain.
Part 2: Test for Starch
13. Clean test tubes #1, 2 and 3 from Part 2.
14. Add ten drops of water to test tube one, ten drops of starch solution to test tube two and 10
drops of unknown to test tube three. (make sure you gently swirl the known containers before
taking your sample)
15. Add three drops of Iodine solution to all three tubes.
16. Compare your unknown in test tube #3 to test tubes 1 and 2, to determine whether or not your
unknown contains any starch. Record your observed colors in the data table.
17. Answer questions f-i.
Part 3: Test for Protein
18. Clean test tubes #1, 2 and 3 from Part 3.
19. Add ten drops of water to test tube #1, ten drops of gelatin solution to test tube#2, and ten drops
of unknown to test tube #3.
20. Add ten drops of Biuret’s Reagent to all three tubes (Caution: Biuret’s Reagent is corrosive, if
you spill any reagent on your skin or eyes, wash it off with plenty of water--and tell your
instructor!)
21. Hold all three test tubes against a piece of white paper and record the resultant colors in your
data table and answer questions h-k.
22. Clean test tubes #1, 2 and 3 from Part 4 and leave them upside down in your test tube rack.
23. Leave your station and lab table set-ups as it was when you arrived or as indicated by your
instructor.
*Points will be deducted during lab for incorrect procedural steps performed by students. This
includes failing to wear or correctly wear safety goggles, boil all tests, contaminate your
unknown, or use up all your unknown in one test etc..
Data Table:
Fill in the color that each respective test tube looked like at the end of each testing procedure. You
must recopy this filled in table for your final write-up.
Test Result Colors
Tube #
1
2
3
Simple Sugar
Starch
Protein
Data Analysis:
a. Why use a separate pipette for the unknown solution?
b. What was the initial color of all three solutions, with Benedicts reagent, just before you
heated them?
c. What is the final color of test tube #2?
d. What is the function of test tube #1?
e. What is the color of a positive test for simple sugar?
f. What is the color in test tube #1 after iodine was added?
g. What is the color of test tube #2 after iodine was added?
h. What is the function of test tube #2?
i. What is the color of a negative test for starch?
j. What is the color in test tube #1 after Biuret’s was added?
k. What is the color in test tube #2?
l. Think of another way this procedural testing (using chemical reagents to look for a color
change) can be used. This should have nothing to do with checking for food chemical.
Explain your example. (2 pts)
Conclusion:

Give me your unknown letter (again) and support or reject your hypothesis about what your
unknown contained? Be sure to tell me your exact results for each test (reagents, your unknown
color and why it was a sugar, starch or protein.) If you don't refer to the specific colors for all
the tests then you will lose up to 6 points. You will automatically lose 4 pts if you get 1 out of
2, or 2 out of 3 correct for your unknown. (Total is 11pts)

Error analysis is required. Remember that this is not a spot to tell me where you went wrong,
but rather a reflection back on the lab to see where disagreements or dissimilar results may
have occurred.

Suggestions are required. It’s easy criticizing something, but you must give me a way to correct
the error(s) you mention.