Science Buddies: "Ask an Expert"

My daughter wants to measure the amt of CO2 released into flasks containing soil with various types of fertilizer. We read about a project meauring CO2 bubbled into water but not how to directly measure it in the air in an enclosed system. Is there a technique that would be doable for a middle school student and not involve equipment that would be outrageously expensive?

Hi Sandy, unfortunately the best way to do this is with outrageously expensive equipment (>$500 at least)! Accurate measurement requires a CO2 sensor or probe mounted inside a flask that is sealed air-tight. Many professionals (HVAC / refrigeration technicians, environmental scientists etc.) use these regularly though the exact type may vary between applications. I would suggest trying to contact someone in these fields (either a professional or someone at a local university) to see if they can help.

The only other ways I know to do this involve chemicals. Typically the gas is passed over a reactive absorbent that changes color when exposed to CO2 (see method 2 in first link below). This could be less expensive depending on how many samples you need to analyze (see link 2 below), but it won't be as accurate as using a sensor. You would also need to know roughly how much CO2 will be measured so you can choose the right tube.

http://www.woodrow.org/teachers/esi/199 ... plingtubes

http://www.zefon.com/store/gastec-carbo ... tubes.html

Good luck!
Ryan

Hi,

If you are satisfied with not getting a quantitative result, just a comparative result within your sample set, the following resources might give a cheap but adequate answer. The first link is to a seven page description of using an indicator solution to detect CO2 given off by respiring organisms. You can access the additional pages by changing the page number in the box on the page or scrolling down with the mouse:

www.pbs.org/saf/1304/teaching/teach.pdf

This resource is a paper that describes making a device to measure CO2 evolution from small biological samples out of micro titer plates. They describe ways to make quantitative measurements, but it is a professional level paper so may be hard to read:

http://Aem.asm.org/cgi/content/full/69/6/3593

Good luck with your project. It sounds like it will be fun!

Best regards,

Barrett Tomlinson