The document is a student's report on a yeast experiment investigating how the amount of yeast affects the amount of carbon dioxide produced. The student's hypothesis was that more yeast would produce more carbon dioxide. The results supported this, showing that as yeast amounts increased from 2g to 4g to 6g, the average carbon dioxide produced also increased from 21cm3 to 39cm3 to 72cm3. However, some trials showed inconsistencies. In the conclusion, the student evaluates weaknesses like a moist collection tube and issues with the scale that affected some results.

1. Marley Emerich
Grade 9
Biology/Chemistry
Yeast Experiment
Beijing BISS International School
School Code: 1123
Wednesday, November 2, 2011

2. Name: Marley Emerich
Partners: David Shong (De Wei)
Date of experiment: Monday, October 17, 2011
Does the Amount of Yeast Affect the Amount of Carbon Dioxide
Produced?
Aim: The aim of the experiment is to investigate if the amount of yeast added affects the
amount of carbon dioxide produced.
Hypothesis I think that with the more yeast we put in, the more carbon dioxide it will
produce. Therefore, the amount and speed the tube is pushed out by the carbon dioxide
should increase as well. When yeast is mixed with sugar and water it creates a reaction.
When all these chemicals react to each other, they produce carbon dioxide. If I put more
yeast into the mixture than before, the sugar will have more to react to. Therefore,
creating even more carbon dioxide. More carbon dioxide should increase the pressure on
tube more, therefore pushing it down faster.
Variables:
Independent variable: The variable that will be changed is the amount of yeast.
It will be changed by each time measuring a different
amount of yeast on the electronic scale and adding it.
Dependent variable: The variable that will be measured is the amount the tube goes
down in 10 minutes. After 10 minutes, I will look at the scale on the side of the cylinder
and see how much it went down.
Control variables:
Control variable #1: Time
I will keep it the same by: Using a stopwatch to make sure each trial lasts 10 minutes.
Control variable #2: Amount of Water
I will keep it the same by: Making sure I fill the measuring cylinder up to 100 mL each
time.
Control variable #3: Amount of Sugar
I will keep it the same by: By using the electronic scale to measure 5g of sugar each time.

3. Control variable #4: Cylinder and Conical Flask
I will keep these the same by: Using the same sized cylinders and flasks every time.
Materials:
• Gas Collection Tube
• Measuring Cylinder using 100 mL of water (to get an accurate reading of the
amount of water for the conical flask.)
• Stopwatch (for timing the amount of time each trial is, 10 minutes).
• Rubber tube with cork (that transfers the carbon dioxide from conical flask to gas
collection tube).
• Conical flask (where the Xg yeast and 5g sugar mix is in).
• 45g of sugar
• 36g of yeast
• A small bowl to place the yeast and sugar in for weighing.
• An electronic scale for weighing the sugar and yeast.
• Glass rod to mix the yeast and sugar with.
• Pen, paper, and notebook to record my data with.
Diagram:

4. Method:
1. Set up equipment as shown in Diagram 1
2. Measure 5g of sugar, 2g of yeast on the electronic scale.
3. Fill up the measuring cylinder to 100 mL of 40˚ water.
4. Transfer this water into the conical flask with yeast and sugar ready.
5. Pour the yeast and sugar in the conical flask and mix with glass rod.
6. Seal it with the rubber tube and cork connected to the gas collection tube.
7. Wait for 10 minutes and stop the timer.
8. Record how much the CO2 has pushed the tube out in cm³.
9. Collect data.
10. Repeat Steps 1-9 except increase the amount of yeast by 2g each time.
11. Repeat the whole experiment two more times.
Results:
Amount of CO₂ Produced With Different Amounts of Yeast
Amount of Trial 1 – Trial 2 – Trial 3 – Average -
yeast (cm³) (cm³) (cm³) (cm³)
(grams)
2 16 25 23
21
4 33 40 44
39
6 87 62 68
72

5. Conclusion:
My hypothesis was correct. The hypothesis was that when I increased the amount
of yeast in the water and sugar mixture, it would produce more carbon dioxide, therefore
increasing the amount of pressure on the gas collection tube. This pushes it out more and
more depending on the amount of carbon dioxide produced. The data shows that with
each added two grams of yeast, the amount of carbon dioxide produced increased
immensely. As you can see in my graph, in each trial the pattern of the carbon dioxide
increasing was consistent. The trend continues on and my data supports my hypothesis,
even though there were some minor errors. My data was mostly reliable because there
were some sections that had some mistakes in them. Like in the first trial using 6 grams
of yeast I measured 87 cm³ when the 10 minutes was up. While in the second and third
trial I got two smaller but closer numbers, 62 and 68 cm³. The same thing happened in
the 1st trial using 2 grams of yeast instead. I got 16 cm³ which was low compared the
second and third trial 25 and 23 cm³ difference. The same happened with the 4 grams of
sugar on the 1st trial. The amount moved was 33 cm³ but the second and third trial was 40
and 44 cm³. Something either went wrong in the first trial or in the second and third trial.
But even though the data may have been a bit unreliable at first, the pattern continued to

6. increase steadily over the next two trails getting the averages of 21, 39, and 72 cm³.
Something that was hard to measure was the amount of yeast and sugar. I put both of
these on an electronic scale to measure the right amounts but sometimes the scale would
be a little off or the paper the yeast or sugar were sitting on would add to the weight,
giving me measurements that were a little off.
Evaluation:
Weaknesses in my Specific Effect on my Improvements I
Method Data Could Make on my
Method
Gas Collection Tube being The tube being moist I didn’t realize how a little
moist – caused it to stick to the dampness could affect a
In the first trial, I had taken
inside glass, enabling the whole trial. Next time not
a tube from right next to thegas to push it down only will I make sure it’s a
sink and dried it. I thought properly. Once I realized completely dry tube, but I
it was dry enough but it what was happening, I will not shake or touch
wasn’t. shook the conical flask a anything in the process
little and it pushed way far because it could push the
up to 87 cm³, which wasn’t tube to a point it shouldn’t
very accurate. be.
Weighing the yeast and On both days, our scale was Next time, I really should
sugar properly - a bit broken. It didn’t sit make sure they my
In order to get a consistent right and would move every electronic scale is not
and accurate amount I time I touched it, causing broken so I can get the same
needed to weight the the measurements to amount of yeast and sugar
amount of sugar and yeast change. I also had to place each time. Also, I should
each time on the electronic the yeast and sugar on a not use a paper to place
scale. piece of paper, which also yeast and sugar in because
weighed some, causing the it changes the results quite a
measurements to all be a bit bit.
off and possibly different
each time.
The temperature. The I performed this experiment Improvements I could make
temperature in the room and on two different days. The based on these problems are
of other elements (maybe first time I did it, the one, next time measuring
the water) affected some of temperature in the room and the temperature of the room
my results. of some of the materials each time so I can consider
was different. The next day that in my data or trying to
the two trials I did were reduce or increase the
very close most likely temperature in the room. Or
because they were on the doing the experiment the
same day. Also, sometimes same day. Also, next time I
when I took out the water use heated water I should
which should have been at pour it and time how long it
40˚ I left it sitting for longer is sitting by itself and how
times then others when long it sits with the yeast
preparing which could have and sugar so I can consider
had an affect on each result. that in my results.