Science Buddies: "Ask an Expert"

Hi, I'm currently in the process of creating the design for my experiment.
In my experiment, I'm testing out which of the three vitamins ( B,C,D) will show the greatest effect towards the yeast CO2 production.
I am planning to construct my own gas collection apparatus to measure the amounts of the CO2.
This is my procedure.
• Boil the 1 cup of water and let it cool until it is about 110°F.
• In a 16.9 fl oz. water bottles, pour the cup of water into the bottle.
• Add one teaspoon of yeast, and 2 tablespoons of into the bottle, and stir gently.
• Repeat for all 20 water bottles.
• In 5 of the water bottles place 2 drops of a vitamin B concentration liquid into each bottle, and stir gently.
• Repeat with the remaining 10 bottles with vitamins C, and D. Leave 5 water bottles without any vitamins. This will be the control group.
• Tightly seal the cap for every bottle when completed.
• CO2 will be collected from the yeast by displacing water (milliliters) trapped in the inverted graduated cylinder (100 ml). The gas collection apparatus will be constructed as so:
1. Fill the plastic tub with water.
2. Fill the graduated cylinder with water by tipping it on its side inside the tub. Keeping the opening of the cylinder under water, turn it upside down and attach it to the side of the tub with strong tape.
3. The graduated cylinder is upside down full of water and with its opening under the surface of the water in the tub.
4. Make a hole in your bottle cap, just big enough to insert the plastic tubing.
5. Insert a piece of plastic tubing through the hole in the cap.
6. Seal the tube to the cap with silicone sealant.
7. Connect the plastic tubing to the gas collection apparatus.

• Leave the water bottles for two days.
• After the two days, measure the displaced water (milliliters) in the graduated cylinder to observe the different amounts of CO2 collected for the varying vitamins.

What are your opinions toward this? Any advice? Anything I could add on, take off ?

Hi msanony,

First, I want to congratulate you for coming up with a unique project idea based on what you found on the Science Buddies site. Very cool! Secondly, I want to thank you for being so thorough with your posting. It really helps the Experts if you give that kind of detail.

I see that you used the procedures for gas collection in the "Aerobic Exercise" project (https://www.sciencebuddies.org/science- ... #procedure). In that procedure, it says the yeast solution should start foaming within 5-10 minutes, and that you should collect CO2 for 30-60 minutes (the same time for each treatment). Thus, I think 2 days might be too long for checking your results. Try checking at 30 or 60 minutes so you don't miss any differences!

I also think you might want to add the vitamin drops to the water before adding the yeast, so you have time to put your gas collection apparatus together before the mixture starts foaming. You may need to perform each trial in sequence (instead of all at once), to make sure you catch everything. (If you wait until all of your bottles are assembled, you may have missed some of the CO2 being produced in the first bottle.)

Other than that, your experimental design looks good. You have replicates (5 bottles per treatment) and a good control (bottles with no vitamins).

Do you have a hypothesis as to how the vitamins might affect CO2 production by yeast? Which vitamin do you think might affect things the most? Try thinking about the chemical reaction involved in CO2 production by yeast, and how each of the vitamins might (or might not) affect that reaction. Remember to think about pH, which affects the solubility of CO2 in water. Have you considered measuring the pH of the vitamin solutions prior to the experiment (and possibly again after the experiment)?

I hope this helps. Please post again (in this same thread) if you have more questions.

Heather