If we put yeast in the acidic, neutral, and basic mixtures, the one in the neutral will allow the yeast to expand and raise the gas pressure because if the pH level is too high or too low it will not allow the yeast to react to its full potential.
Results:
When putting in the hydrogen peroxide, the measurement was approximate, and therefore there may have been less or more of the chemical, but the amount of it in all three of the test tubes was equal.
The first group of tests we did had been done incorrectly, but our mistake wasn't noticed until we already tested the first two of the tubes. Instead of only putting in two drops of the yeast solution like we were supposed to, we accidentally added 3mL, which was way too much. The following results were from the incorrect amount of yeast.
When testing the acid, the pressure skyrocketed and the solution fizzed to almost the middle of the test tube upon the addition of the Diet Coke. Once the air pressure hit 126 or so, the sensor plug actually popped off. When we reattached the plug, the pressure raised again and once it hit that 126-130 spot it popped off again. This reaction had occurred three times before we when on to the next mixture.
Next, we tested how the yeast would react to the neutral. This one had similar results to the acid, but the bubbles raised higher and we held down the top of the lid. The air pressure of the yeast and Skim Milk mixture reached about 158. It was at this point that we were considering possible mistakes that may have been made because not many other groups were having even similar results. Our group looked over the procedures again and saw that we were only supposed to put three drops of the yeast solution into the acid, neutral, or basic test tube. After discovering this, we scratched what we had already done, cleaned the materials, and got ready to start again. This next time, we only put in the 2 drops as the procedures directed.
When testing the acid there was a steady scale upward, but there was not much of a physical reaction, besides slight bubbling. The pressure started at 98 and ended at 104.5.
When we added the neutral base, the pressure slowly rose, becoming considerably higher then the other. The pressure started at 100 and ended at 105.4.
The last test, the base looked like it was going to split the acid and neutral right down the middle in the graph, but it leveled out almost right away so it ended with the lowest pressure. The pressure started at 98.81 and ended at 101.6.
This graph shows the air pressure of the yeast when added to three different substances. The red was the acid, blue neutral, and green base. In order from highest to lowest air pressures, there was the neutral, acidic and base.Conclusion:
My hypothesis was supported by this experiment because the neutral mixture, which consisted of skim milk and Hydrogen Peroxide, gave the greatest reaction and provided the highest air pressure. It worked for the reasons that I predicted in my hypothesis, since the pH level in the acid, Diet Coke, is too high and the pH level in the base, Stomach Antacid, was too low, they did not allow the yeast to react to its full potential. Since the skim milk was neutral with its acidity level in the middle, it did let the yeast react as much as it could. One thing I learned from this experiment was how important it really is to read the directions. Luckily, since this is just an 8th grade science lab, it probably will not affect me very much in the rest of my life. But, the same principle can be applied to many, many aspects of the real world. For example, if someone were to be driving their care down the road and wasn't paying attention to the traffic lights (the "instructions") they may end up being in a car accident and could lose their life, or take the one of the other person in the accident. The entire first part of our experiment was a complete mistake, but since we redid it from the beginning, keeping the correctly made yeast solution, the actual results were not affected.
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