Qualitative Testing for the Presence
of Carbohydrates and Proteins
Purpose
To conduct qualitative tests that reveal the
presence of carbohydrates (simple sugars and
starch) and proteins.
Lugol’s Test for Starch
1. Label 4 test tubes starch,
protein, glucose, and
distilled water.
2. Place 10 drops of Lugol’s
solution (iodine) into each
test tube
3. Record the initial color of
the Lugol’s iodine.
4. Add 1 ml of starch,
protein, glucose or
distilled water to the
appropriate test tube.
5. Record the final color of
Lugol’s iodine.
Lugol’s
iodine
Starch
Lugol’s iodine
solution + starch solution
Benedict’s Test for Simple Sugars
1.
2.
3.
4.
5.
6.
Label 4 test tubes: starch,
protein, glucose, and distilled
water.
Add 1 ml of the Benedict’s
solution to each test tube.
Record the initial color of the
Benedict’s solution.
Add 1 ml of the appropriate
substance to each test tube.
Heat the test tubes in a hot
water bath for 5 minutes.
Record the final color of the
Benedict’s solution.
Benedict’s
solution
After heating Benedict’s
solution with different
simple sugars
Biuret Test for Proteins
1. Label 4 spots on the spot
plate: starch, protein,
glucose, and distilled
water.
2. Place 10 drops of Biuret
solution to each spot.
3. Record the initial color of
the Biuret solution.
4. Add 10 drops of starch,
protein, glucose or
distilled water to the
appropriate spot.
5. Record the final color of
Biuret
Biuret solution
+ protein
Biuret
solution
Qualitative Testing for the Presence of
Carbohydrates and Proteins in Unknowns
• Purpose – To conduct and interpret qualitative
tests to determine if an unknown contains
simple sugars, starch and/or protein
Identifying Unknowns
Hypotheses
• If an unknown contains a simple sugar, then
when _______ is added to it, the indicator will
turn _____ because
• Repeat for starch and protein
Homework
• You will be given 3 unknowns and will
determine whether each unknown contains
simple sugars, starch and/or protein.
• Your homework is to write out a step by step
procedure of the tests you will conduct to
determine what your unknowns contain.