Apparatus required per class group of 24 students
Yeast
Glucose
Distilled water
Sodium hypochlorite solution (15% w/v)
Potassium iodide solution (10 % w/v)
Conical flasks
Graduated cylinder (250ml)
24
12
Graduated cylinder (50ml)
Beaker (250ml)
Beaker (50ml)
Boiling tubes
Thermometer
Funnel
Filter paper
Timer
Labels
24
24
24
24
12
12
12
12
12
Syringes (5 ml)
Rubber bungs
Fermentation locks
Electronic balances
24
24
24
3
Weigh boats
Incubator
Waterbath 1
The apparatus for this experiment lends itself to being preprepared in a ‘box of equipment’ – see Section 1.
Biology SLSS 2009
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1
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Advance preparation o Prepare solutions o Set incubator and water bath.
Advance chemical preparation
(a) 10% w/v Glucose solution o Dissolve 20 g of glucose in 200 ml of distilled water. o Each group will require 2 x 200 ml batches of solution.
(b) Sodium Hypochlorite Solution o Add 1-2 pellets of sodium hydroxide to sodium hypochlorite solution. o This solution should be kept in a tightly sealed container. or o Weigh out 15 g of sodium hypochlorite and make up to 100 ml with water.
(c) Potassium Iodide Solution o Dissolve 10 g of potassium iodide in a small amount of distilled water. o Transfer the solution to a volumetric flask and make up to 100 ml.
Safety precautions o Sodium hypochlorite is highly corrosive and causes severe burns. It is harmful if inhaled, in contact with skin or if swallowed. For further information see MSDS.
Expected outcome of experiment o This experiment produces alcohol at a low concentration.
o A positive iodoform test results in the formation of yellow crystals in the boiling tube.
Disposal and post-experiment work o Excess glucose solution can be stored in the refrigerator.
o Potassium iodide can be flushed to a foul water drain.
o Sodium hypochlorite should be kept for chemical disposal.
For the datalogging method for this experiment, please see Section 3.
Biology SLSS 2009 2

Apparatus required per group o 10 g of Yeast o 400 ml Glucose solution o Sodium hypochlorite solution o Potassium Iodide solution o 2 x Weight boats o 2 x Conical flasks o Graduated cylinder 250 ml o 2 x Graduated cylinders 50 ml o Beaker 250 ml o Beaker 50ml o 2 x Boiling tubes o Thermometer
Assembled apparatus o Funnel and Filter paper o Timer o Label o 2 x 5 ml syringes o 2 x Rubber bungs o 2 Fermentation locks o Electronic balance o Stirring rod o Weigh boat o Incubator (30 O C) o 2 Droppers o Water bath (50 O C – 60 O C)
Biology SLSS 2009 3

Method
To produce alcohol using yeast:
1. Prepare 400 ml of a 10% w/v glucose solution.
2. Into each of the two conical flasks, add 200 ml of the glucose solution.
3. To one of the conical flasks, add 5g of yeast and swirl. Label this ‘yeast + glucose’.
4. The second flask acts as a control
– it has no yeast. Label this ‘control’.
5. Half fill two fermentation locks with water. Attach one fermentation lock to each flask.
6. Place both flasks in an incubator at 30 O C overnight.
To show the presence of alcohol: Iodoform test for alcohol.
7. Remove both flasks from the incubator and filter the contents of each into separate boiling tubes and label as before. Filter until 3 ml of each is collected.
8. To each boiling tube, add 3 ml of the potassium iodide solution and 5 ml of the sodium hypochlorite solution.
9. Warm gently for 4-5 minutes in the water bath.
10. Allow to cool and observe any changes.
11. Record and compare results.
12. Replicate the investigation or cross reference your results with other groups.
13. At the end of the experiment, clean all of the equipment and replace it in its correct place.
Results:
Flask Original colour of filtrate
Final colour of filtrate
Other changes
Yeast + Glucose solution
Control (no yeast)
Conclusion/Comment
Biology SLSS 2009 4