Science Buddies: "Ask an Expert"

Hi,
I am researching the project "Yeast Metabolism with and without aeration" and it doesn't say a way to measure the CO2 output. I read the procedure countless times but it doesn't say how to measure the CO2. Can someone please explain it to me. Thanks

Srikar Sirvisetty

Hi Sirkar,

For this experiment you'll be measuring the CO2 produced by capturing it in a gas collection device. This device is detailed in the procedure and includes using tubing to direct the CO2 into an inverted graduated cylinder filled with water. As the Yeast produces CO2 it will displace the water in the graduated cylinder.

Before you add the yeast to the sugar/water mixture you should record the volume (in mL) of gas in the upside-down graduated cylinder. Then add the sugar/water mixture to the yeast and quickly cap the bottle with the tubing attached that directs the CO2 formed into the graduated cylinder. When you've completed your test (use the same length of time for both +air and -air tests) again record the volume of gas (in mL) in the upside-down graduated cylinder. Subtract the starting volume from the ending volume and you will calculate how much CO2 was produced by the yeast.

https://www.sciencebuddies.org/science- ... #procedure

Good luck,

Audrey

So, the carbon dioxide output is measured in ml? How does that work?
Thanks
Srikar Sirvisetty

Hi Srikar,

(Sorry I just noticed I had a typo in your name in my previous reply - my apologies!) Carbon dioxide at room temperature and pressure is a gas so we can measure in it units of volume. The carbon dioxide generated by the yeast will "push" some of the water out of the graduate cylinder so you can see the volume collected. You can then use the measurement lines in milliliters on the graduated cylinder to measure how much carbon dioxide was captured.

Good luck,

Audrey

So the amount of water that leaves the graduated cylinder is the carbon dioxide output correct? And the water that leaves the graduated cylinder goes to the squirt bottles?
Thanks
Srikar

Hi Srikar,

Correct - the volume of water that leaves the graduated cylinder is the volume of carbon dioxide that is created. The carbon dioxide displaces the water. The water that is displaced from the graduated cylinder will go into the square dishpan, not the squirt bottle.

See Figure 3 in the Procedure that has the graduated cylinder upside-down in the dishpan full of water.: https://www.sciencebuddies.org/science- ... #procedure

Good luck,

Audrey