Acid Base Lab

At the beginning of the lab my group and I developed a problem and a hypothesis. Our problem was "How does yeast react with acids and bases?" Our hypothesis was "If we mix yeast with various acids and bases, then we will get different outcomes for each one, with the acid producing the largest reaction." After running our tests, my hypothesis was completely incorrect. The first test we ran was the acidic test. We added yeast to the cola and hydrogen peroxide mix and then put on the stopper and swirled it around. Then, we connected the tube and recorded our results for two minutes. At about 130 kPa the stopper popped off. We put it back on and hoped for the best. To our surprise, it rose again to 132.63 kPa. We concluded that the pressure would have been MUCH higher if the top did not pop off. The next test we did was the neutral test, a mixture of silk milk and hydrogen peroxide. This surprisingly had the highest pressure at 177.18 kPa. The pressure popped of of this one too, but this occurred after the test was finished. Our third and final test was the basic test. This reached a pressure of 164.7 kPa, but popped during the experiment. With this one, we also thought that the pressure would be much higher. In my opinion, if the stoppers did not pop, the basic would have the highest pressure, the neutral would have the second highest pressure and the acidic would have the lowest pressure. Unfortunately, we may never know.

Focus Questions:

Q: In which mixture was the yeast activity the greatest?

A: The yeast activity was the greatest in the neutral mixture, because the pressure rose to 177.18. I also know that the yeast activity was the greatest in this one because when the stopper came off, it frothed almost to the point of overflowing. In the other ones when the top popped of the froth disappeared along with the air pressure. During the experiment (with the stopper on), the froth rose to over half the height of the test tube.

Q: In which mixture was the yeast activity the lowest?

A: The yeast activity was the lowest in the acidic mixture, because the pressure rose to 132.63. Also, when the stopper came off there was no foam left at all. The only thing that could be found was the cola at the bottom and the residue along the walls. During the experiment (with the stopper on), the froth barely rose at all.

Q: What can you conclude from the results of the experiment?

A: After the experiment, I can conclude that the yeast reacts best with the base and the worst with the acid. Knowing this, I think that yeast reacts best in a neutral mixture. If a mixture is more basic it reacts slightly less, but if the mixture is more acidic then the reaction will be MUCH smaller.