Acid and Base Yeast Lab

Our test today involved yeast (REALLY starting to hate this smell), hydrogen peroxide, Diet Coke, stomach antacid, and skim milk. We also needed a gas pressure sensor. So, here's the low down on what we did:

First,

we filled each tube with three mL of hydrogen peroxide (six squirts from the eyedropper). We were given three strips of sticky notes to which we wrote "A" (for acid) on one, "N" (for neutral) on another, and "B" (for base) on the last before placing the sticky notes under the first, second and third tube. Then we added three mL of Diet coke to the first tube, three mL of skim milk to the second tube, and three mL of antacid to the third tube.

Now

that the set-up was done, we created the "Yeast Suspension." Why it is called "Yeast Suspension," I am not sure considering the yeast wasn't at any point suspended in the air or halted at any point (I hope that doesn't mean we did it incorrectly). The way we created this (whether it be right or wrong) was by filling 20 mL of water into the graduated cylinder then pouring that into the beaker. Dean added half a teaspoon of yeast to the water which we then stirred to mix it all up. That was our "Yeast Suspension."

Lastly

we filled up the eye dropper with our watery yeast from the "Yeast Suspension." In the first test tube, Tube A, we dripped in two drops of yeast. Then using the black stopper from the gas pressure sensor (the tubing of the pressure sensor was disconnected form the stopper at this point). We gave the tube a quick couple of good swirls before setting it back in the rack and attaching the the rest of the pressure sensor to the stopper before clicking "Collect." For two minutes it sat there and collected. Once it was finished, we clicked "Stop" then clicked "Store Latest Run" before moving onto the next tube.

One thing we noticed was that the yeast looked really good (like yummy good, despite the awful-smell). It resembled kids coffee (which is something we have in our family that is basically 1/4 coffee with 3/4 milk) which is one of my favorite breakfast drinks. Good thing the smell made me want to gag otherwise I might have accidentally mistook it for my drink. Another thing was that with the soda, by the end of hte run, it had turned a lighter shade of brown. The milk was interesting in the fact that it had about two or three centimeters of bubbles on the top. Antacid also had bubbles, but it was more like a centimeter of bubbles. The milk easily had three to four times more.

Our results were this:

A (Acid):

Pressure at the beginning of the test--101.31.

Pressure at the end of the test--106.23

(Acids--Red)

N (Neutral):

Pressure at the beginning of the test--99.48

Pressure at the end of the test--104.1

(Acids--Red; Neutral--Blue)

B (Base):

Pressure at the beginning of the test--99.89

Pressure at the end of the test--106.73

(Acids--Red; Neutral--Blue; Bases--Green)

(Note: You cannot see the acids in the last picture because acids and bases had a similar incline)

So from our tests, we concluded that bases BARELY had the most pressure build up, with acids less than a unit off. Neutral trailed behind some, but had the most bubbles. I think that is because perhaps there was sugar in the milk that the yeast ate, but the soda has sugar also which didn't have as many bubbles. So we are not sure how to conclude that fact.