Science Buddies: "Ask an Expert"

Hello -

I watched a NOVA Science show where a student removed carbon dioxide using sodium hydroxide. I've searched every where for information on how to do this, but can't find any specific set ups for the process. I know that Sodium Hydroxide is a base, carbond dioxide an acid and they create a acid base reaction removing the Carbon Dioxide. My question is on the test experiment. How can I measure if the CO2 was removed from the air? How can I prove it was a success? I looked at CO2 monitors and they cost hundreds of dollars. I wrote to the student who did the experiment (Claire Lackner) as well as her dad and have not heard back from them. I know the process is used in rebreathers, but can't find a similar experiment. Can someone help me? Alyssa

Hi,

Testing for carbon dioxide is pretty easy. One standard test is to bubble the gas through calcium hydroxide - calcium carbonate will precipitate out as a chalky white solid. You should be able to get calcium hydroxide through your local pharmacy (drugstore) by special order (probably next day delivery). It is also called slaked lime or calcium oxide will also work if dissolved in water. Some web references:

http://www.infoplease.com/ce6/sci/A0809855.html

http://www.gcsescience.com/itestcarbondioxide.htm

http://scifun.chem.wisc.edu/CHEMWEEK/lime/lime.html

http://en.wikipedia.org/wiki/Calcium_carbonate

Hope this helps.

Best regards,

Barrett Tomlinson

It sort of does and sort of doesn't. Using the method you discuss I could show that there is Carbon Dioxide, but I couldn't measure it in any way, or would it change the weight of the solid? I'd like to try and figure out how much carbon dioxide is removed by using the process versus how much would be needed to generate the electricity to run the electric pump. Maybe I'm in over my head here.

The NaOH will remove carbon dioxide and I suppose that performing the test you suggest before and after I've introduced carbon dioxide to the NaOH would show that it has been reduced but not quantify the amount. Is there anyone who can help me with this? Can I dry the NaOH after it has been exposed to carbon dioxide and see if there is a change in the weight?

Hi,

In your shoes I would look into titrating the sodium hydroxide with acid to a pH near the pKa of bicarbonate- carbonic acid dissociation. You can then get the amount of carbon dioxide absorbed by the difference of the acid required to neutralize the same size aliquot of fresh sodium hydroxide and the Carbon dioxide exposed sodium hydroxide.

Good luck!

Barrett Tomlinson

Thank you for the help! My dad found someone through his work that has a Drager testing kit and actually has the tubes for carbon dioxide that they are going to let me use for the experiment (he just told me he found them). I appreciate the help and will keep you updated. Do you think this experiment will be a good one?

Hi wvparkers,

Re: "Do you think this experiment will be a good one?", please consult the Steps of the Scientific Method:
https://www.sciencebuddies.org/science- ... thod.shtml thanks.
As long as you can come up with a question, testable hypothesis, etc., meet other constraints like time and budget, it's a good project.