CARBOHYDRATE LAB
Objective: To establish test protocols for the detection of starch and sugar, and to
understand the limitations of each test.
Materials:
Iodine solution ** avoid eye/skin contact, stains skin and clothing (it stains) **
Benedict’s solution ** avoid eye/skin contact
Small beakers (100 - 250 ml)
Test tubes
Test tube rack
Test tube holder
Hot plate - Beaker of water (about 90o C)
Starch solution (positive control for starch)
Glucose solution (positive for reducing sugars)
Solutions of fructose, sucrose, lactose, maltose, methyl cellulose, etc...
Plant tissues (potato, carrot, radish, apple, orange, etc...
Other materials to be tested
PREPARE A SIMPLE TABLE FOR RECORDING YOUR RESULTS
TEST FOR STARCH
Put several drops of iodine solution into a small test tube containing a small amount of starch
solution.....describe the results of this positive control.
(Note: Use white paper for a background for better color detection.)
Repeat with a test tube containing a small amount of water....describe the results of this
negative control.
Test for the presence or absence of starch in a variety of materials in a Petri dish. Note:
Fresh food will not show results immediately as does the starch solution. Give unknowns
time for the starch solution to diffuse into cells/tissues.
Prepare a table for your data (“Iodine test for starch”)
TEST FOR SUGARS - Note: Benedict’s test will be positive only for ‘reducing’ sugars
(simple aldehyde sugars). Reducing sugars are able to donate free electrons to the copper
compound in the test reagent, resulting in a color change. Glucose is a reducing sugar.
Put about 10 drops each of sugar solution and a few drops of Benedicts solution into a
test tube.
Place the tube into hot (almost boiling) water for 3-5 minutes.
** Glucose is positive; water is negative **
Test other sugars, starch solution, soft drinks, etc...
Try diluted solutions of known positives.
Prepare a table for your data (“Benedict’s test for sugar”)
QUESTIONS
What are the limitations of the iodine test?
What are the limitations of the Benedict’s test?