| Biology demonstration manual |
Lesson: Les ailments
Rationale: Test for the presence of glucose in food samples.
Sodium carbonate (Na2CO3) (science kit)
Copper sulfate (CuSO4) (science kit)
Sodium citrate (I had this sent from the States.)
test tubes (IycÃ©e) (or glasses)
needle and 5 ml syringe (pharmacies)
balance (IycÃ©e) (or make one with the science kit manual.)
graduated cylinder (science kit)
Suggestions for food sample:
Positive: milk, banana, sweet potatoe
Negative: manioc flour, peanut butter, oil
To prepare solutions:
1. Fehling's solution:
This is actually Benedict's solution but since the French use Fehling's, I tell the student's that it is Fehling's. The two solutions react the same but Benedict's isn't caustic and keeps longer.
a. Dissolve 17.3 g of sodium citrate and 10 g of Na2CO3 in 80 mls of warm water.
b. Dissolve 1.7 g of CuSO4 in 20 ml of cold water.
c. Add the CuSO4 solution to the sodium citrate solution while stirring.
2. Start a water bath.
3. For liquids (milk, oil) add I ml to a labeled test tube. For solids (flour, peanut butter, banana) mix or mash in I ml of water.
4. Add I ml of Fehling's (Benedict's) to each tube.
5. Put the tubes in a boiling water bath for ~ 3 minutes.
6. A red-orange precipitate indicates the presence of glucose.
Note: Fehling's (Benedict's) does not give a red precipitate with complex sugars such as sucrose. Starches will give a cloudy green color.
Source: Mackean Class Experiments in Biology, p. 13; Teacher's Book, p. 4, 19.