4.1 (c) To conduct a qualitative test for reducing sugar
Teacher Notes
Apparatus required per class group of 24 students
Benedict’s solution
48 ml
Boiling tubes
24
Boiling tube rack
12
Boiling tube holder
12
Distilled water
Glucose solution
24 ml
Water bath
1
( or apparatus to set
(12 sets)
up water bath)
Advance preparation
o Prepare solutions.
o Set up water bath.
Advance chemical preparation
(a)Benedict’s reagent (qualitative):
o To make 1 litre. Dissolve 17.3 g copper sulfate-5-water in 200 ml of cold distilled
water.
o Dissolve 100 g anhydrous sodium carbonate and 173 g sodium citrate ( 2hydroxypropane-1,2,3-tricarboxylate) in about 800 ml of warm distilled water.
o When both solutions are cool, slowly add the copper sulphate to the
carbonate/citrate mixture with constant stirring.
(b) Glucose solution (1% w/v).
o Dissolve 1 g glucose in water and make up to 100 ml with water.
1
Safety precautions
o
For further information see MSDS
Expected outcome of experiment
o A positive test for a reducing sugar is a brick red colour
o A negative test for a reducing sugar is a blue colour
Disposal and post-experiment work
o Benedict’s reagent – flush a small amount (50 g) to foul water drain.
o Glucose - flush to foul water drain with water.
4.1 (c) To conduct a qualitative test for reducing sugar
2
Student Notes
Apparatus required per group
o 2 x boiling tubes and rack
o Test tube holder
o 4 ml Benedict’s solution
o 1 ml glucose solution
o Distilled water
o Bunsen, tripod, gauze and 400 ml beaker if necessary.
Assembled apparatus
Method
1. Set up a hot water bath.
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2. Label two boiling tubes ‘A’ and ‘B’.
3. Place 2 ml of the glucose solution into tube A.
4. Place 2 ml of water into tube B. This acts as the control.
5. Add 2 ml of Benedict’s reagent to each tube.
6. Swirl each tube.
7. Place both tubes in the hot water bath and heat for 5 minutes.
8. Using the test-tube holder, carefully remove both tubes from the water bath and place
in the
test-tube rack.
9. Record result.
10. At the end of the experiment, clean all of the equipment and replace it in its correct
place.
Results:
Sample
Initial colour
Final colour
A – Glucose solution
B - Water
Conclusion/Comment
4
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