To investigate the effect of changing the P.H. level during the fermentation of yeast; and to see how much the yeast ferments at the different P.H ’s.

List of apparatus:                Yeast

                        Petri dish

                        Spoon

                        Test tube rack

                        Sugar

                        Weighing machine

                        Warm water (40 centigrade)

                        P.H. buffers 2-11

                        Thermometer

                        10cm³ graduated pipette

                        Boiling tube with bung and delivery tube

                        250cm³ beaker

                        Clamp

                        Glass rod

                        10cm³ measuring cylinder

                        Stop watch

Below is a list of variables, which are to be kept constant for the whole of the Preliminary experiment. Although they may be changed when the proper experiment is carried out.

• Dissolve 8g of sugar in 125cm³ of warm water (40 centigrade)
• Add 15g of yeast and stir well
• Leave for 7 minutes for the yeast to become active

The experiment was set-up as shown on the separate sheet of paper.

1st experiment

• P.H. 3 during fermentation.
• 7 minutes left fermenting
• 5ml CO2 gas

2nd experiment

• P.H. 6
• 7 minutes fermenting
• 15ml CO2 gas

Decisions about Experiment

The preliminary experiment showed the outline of the prediction we made. The first experiment whereby the P.H. was 3 showed that a low P.H. i.e. a strong acid does not produce a huge amount of acids. This is because of the enzymes that are used in fermenting are being killed by the acid. The second experiment allowed us to see that a more neutral P.H does produce a larger amount of precipitate. Both of these results should have been higher than they actually are, this is due to some inaccuracies in the method of this experiment. These problems have to be changed before the proper experiment has been carried out.

The time for which the fermentation was allowed to be left has to be changed. In the preliminary as soon as the method was set-up properly. This did not allow a long enough time for the fermentation to take proper affect. This was because the glass tube linking the boiling tube and the measuring cylinder was full of water. This water has to be pushed back down the glass tube, this slows down the fermentation, and does not allow a vast amount of gas to be collected. To stop this from happening we must start the stopwatch when the gas has actually reached the measuring cylinder. The time allowed for the gas to be collected is too short; it does not give sufficient amount of gas in order to see how the P.H. effects the fermentation. Therefore the time for each experiment is extended to 10 minutes to allow sufficient gas to be collected.