4/11/10

Practical – Monitoring the Fermentation of Glucose

Aim: To investigate the fermentation of glucose.

Hypothesis: The mass of the flask will continue to lower as the carbon dioxide leaves the flask and escapes through the limewater.

Equipment:

- 50 mL Erlenmeyer flask- 5g sachet of dried yeast- 10-20g glucose- 40mL warm water (30-40ºC) –

Actually 36.5- Small beaker- Ordinary Stopper

- Delivery tube and stopper- Small beaker of limewater- Evaporating dish- Thermometer- Safety goggles- Electric balance

Risk Assessment:

Risks Precautions ResponseBroken Glass, dropping equipment

Hold with both hands, place in middle of bench

Use a dustpan to pick up glass. Notify teacher of breakages.

Cutting self on glass Wear gloves if possible, do not directly touch broken glass, place broken glassware in glass bin.

Wash hand under cold water until bleeding has stopped. Apply pressure with bandage to reduce bleeding, if severe, seek assistance or call emergency.

Tripping on bags, cords, chairs Tuck chairs, cords, and obstacles away from open areas. Leave bags outside the classroom

Check for injuries, if injuries present alert teacher, register first aid. Move outstanding items back into place.

Contamination of food, contamination of chemicals

Do not take food in the lab, do not consume any substances in the lab. Read labels carefully, do not return substances to source container.

Any food in the lab should be discarded and not eaten. If medical attention is required after eating food, call poison hotline.

Inhaling or ingesting or being affected by toxic chemical substances (i.e. untied hair, from spills)

Wear safety goggles, waft instead of smelling, place items in fume cupboard when not in use, tie up hair. Measure liquids into beaker before measuring cylinders to avoid spills.

Wipe up any spills immediately, if toxic poisoning has occurred, notify teacher, wash eyes or mouth out with water immediately. No not directly inhale fumes.

4/11/10

Method:

1. Erlenmeyer flask was placed on the electric balance, weighed, recorded and tared. 5g of yeast was then placed in the flask.

2. A beaker of hot water was cooled down by adding cold water as the temperature was continually measured. This was cooled to a temperature of 36.5 degrees Celsius, and then 40mL of the warm water was measured into a beaker.

3. 15g of glucose was measured in an evaporating dish after the dish had been tared. This was added to the flask at the same time as the water, and the stopper added to the flask.

4. The flask was swirled to ensure the contents were mixed, and using a finger to hold the delivery tube closed, the tube was submerged within a small beaker of limewater.

5. The mass of the flask was quickly taken using an electronic balance, reading to the nearest 0.1g. This measurement was repeated after 5 and 10 minutes, the next day, on day 5 and day 9. Any patterns of decreasing or increasing mass were recorded in the results, and observations and unexpected values were recorded in the results and discussion.

Results:

Mass of Erlenmeyer flask = 563 g

Temperature of water = 36.6ºC

Time of Recording (minutes) Mass (g) Mass of Substances (g)0 614.4 51.45 633.3 70.310 633.8 70.8Day 2 638.1 75.1Day 5 637.1 74.1Day 9 629.9 66.9Discussion:

The experiment was testing the effect of fermentation of glucose on the mass of a solution. As glucose fermented (with heat as a reaction booster) with yeast as the catalyst, the molecule broke down into carbon dioxide and ethanol. Carbon dioxide was released through the delivery tube and into the limewater. A white tinged crust formed on top of the limewater as a result of calcium carbonate being formed when carbon dioxide is bubbled through. The calcium carbonate, an insoluble substance cannot dissolve in the limewater and therefore provides a layer on top, preventing the carbon dioxide from escaping.

C6H12O6(aq) (catalyst = yeast, with heat) 2C2H5OH(aq) + 2C02(g)

4/11/10

The mass of the solution should have been reduced at the end of the experiment due to the loss of the carbon dioxide, but the result obtained did not mirror this. First, the mass increased by a large amount, possible due to air being let into the flask. It continued to increase over the next couple of days, but by only a small amount, possible due to inaccurate measurements on the electric balance (due to placement of beaker on table, placement of flask on balance and angle of tube). The produced carbon dioxide in the large flask that was used may have remained within the flask instead of exiting through the delivery tube, increasing the mass of the flask. After day two, the mass began to decrease again by quite a large amount but never reached the original mass of the flask. This suggests that the original measurement of mass was inaccurate, due to human, reading or other errors.

The experiment is fairly reliable as repetitions of measurements were made by each individual, but would have been more reliable if each person collaborated results and made averages to obtain a more accurate answer. Sterilisation of equipment before the experiment, a more exact measurement of reactants and more progressive measuring of masses could have been used to improve the experiment. Also, a smaller flask could have been used to reduce the chance of air entering the flask in order to obtain a more accurate result. The experiment could have also have been made more reliable by using the same electric balance the entire time, from beginning to end of the experiment.

Conclusion:

The reaction of the fermentation of glucose involves the use of heat and a catalyst of yeast. It reduced the glucose molecule into carbon dioxide gas, and ethanol. The mass of the Erlenmeyer flask should decrease as carbon dioxide exits the delivery tube throughout the experiment. Therefore, the hypothesis that the mass will decrease throughout the experiment was not supported by the obtained results, and a number of improvements could have been made to improve the accuracy of this result.