Acid and Base Yeast Lab

How does yeast react with acids and bases?

The hypothesis was that the yeast would be most active in the acidic solution. To test the lab, we added yeast to an acid, neutral, and a base. The yeast was made in a solution so it could be added as a liquid. The air pressure inside of the test tube was taken for each substance once the yeast was added.

For the acid test, the pressure climbed rapidly. At about 130 kPa, the stopper popped, and the pressure plunged. The pressure topped out 132.63 kPa.

In the neutral test, the pressure climbed to 177.18 kPa, and then, again, the stopper popped and the pressure plunged rapidly. The pressure never came back to what it was before the pop.

In the base test, the pressure climbed rapidly. At 164.70 kPa, the stopper popped and the pressure dropped lower than the start and the other two tests.

In all of the tests, the stopper popped. The pressure would have been much higher if the stopper hadn't popped. It is hard to determine which one had the most pressure build-up, because the one that had the "highest" pressure was the one that held out the longest. There is no ability to say which one would have  had the highest pressure. 

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In which mixture was the yeast activity greatest?

The yeast activity was greatest in the neutral mixture. This may have been because it held out longest against the pressure, making it to 177 kPa before the stopper popped. It did get more foamy and frothy than the other ones, so it may have had the highest pressure if none of them popped. This could be because yeast neutralizes hydrogen peroxide, which was in all of the test tubes, and the water just diluted it, it didn't add any other chemicals.

In which mixture was the yeast activity the least?

The yeast activity was least in the acidic mixture. The acidic mixture was also the earliest one to pop, popping at 130 kPa. It was not rising as fast as the others in the beginning, so it would have probably been the lowest pressure no matter what. 

What can you conclude from your results?

From my results, I can conclude several things. One is that the pressure accumulated in the beaker was so great that the stopper actually popped out of it. Another thing is that yeast does not have a major reaction with the acids and bases. I think that a large influence of the pressure came from the yeast neutralizing the hydrogen peroxide.