The Determination of the Presence of Reducing Sugars Using Fehling's 
Solution

Brekke, Stewart E.
6238 N. Hoyne                                     Robeson H.S.
Chicago, Illinois 60659                           723-1700
 
Objectives:

1) to determine the presence of sugar using Fehling's Solution
2) to use laboratory apparatus such as bunsen burner, beakers, test 
   tubes, test tube rack and Fehling's solution 
3) to show that a plant produces sugar such as fructose or dextrose
4) to balance the equation carbon dioxide and water yields fructose
5) to demonstrate common laboratory techniques such as heating a test 
   tube and using beakers and reagents
   
Apparatus Needed: 

1) Fehling's solution (this can be made fresh using a recipe from a 
   suitable text)
2) beakers
3) test tubes
4) test tube rack
5) test tube holder
6) bunsen burner
5) various plant fruits, leaves or roots such as onions, oranges, 
   spinach, lemons (only one slice is needed from each type)

Recommended Strategy:

Crush the slice of onion or lemon in a beaker so that a juice is 
obtained. Then take the extract and pour it into a test tube. Add 
Fehling's solution filling the tube about half way. Attach the test 
tube holder and heat the solution. After a short time a yellow to red 
precipitate will form if the object contains a reducing sugar such as 
fructose or glucose. This is a test for such sugars. Often the students 
will be surprised that there is sugar in onions or lemons because the 
taste is bitter due to acids present. The phenomenological approach can 
be made by first giving a bit of lemon juice to some of the students 
and ask them if they think sugar is present. Most of the time the 
students will say that no sugar is present. Then proceed to test for 
the sugar using the above method.