FACT
WATCH: Watch a
video
demonstration of
the test for glucose.
See video:
SHORTCODEat
http://www.everythingscience.co.za- dropper
Method:- Place a piece of potato or bread and the lettuce leaf in the petri dish.
- Using the dropper add a few drops of iodine solution onto the potato or bread.
Figure 2.11: Experimental set-up: test for the presence of starch using iodine.Observations:Record your observations.Questions:Can this method be used to determinehow muchstarch is present? Explain your answer.Certain monosaccharides, such as glucose, are known asreducing sugars. These are defined
as sugars that can easily undergo oxidation reactions (i.e. lose an electron or gain an oxygen
atom) and act as areducing agent. In order to test for carbohydrates we typically test for
the presence of reducing sugars using either theBenedict’sorFehling’s test. Both solutions
(Benedict’s and Fehling’s) contain copper sulphate which reacts with reducing sugars to
produce a colour change.
Investigation: Testing for the presence of reducing sugars (Essential investigation-CAPS)Aim:To test for presence of sugars using Benedict’s or Fehling’s test.Apparatus:- 4 heat resistant test tubes
- 1 beaker
- bunsen burner or water bath with hot water (+50◦C)
- test tube rack (if using a water bath)
- glucose solution
Chapter 2. The chemistry of life 33