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What tools can, in a very simple home environment, be used to easily measure CO2 levels in the air, for use in a home school science experiment?

Henry Stone
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    Googling “home co2 sensor” brings up a variety of options – Jon Custer Jul 16 '22 at 17:14
  • Those measure overall air quality (the ones I found, anyway). I'm trying to measure plant CO2 production in a closed system, I don't think they'll do the trick, sadly... – Henry Stone Jul 16 '22 at 18:03
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    Ok, ‘greenhouse co2 sensor’ pulls up some others. Including ones for Arduino. – Jon Custer Jul 16 '22 at 19:02
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    Look up Orsat gas analyzer in Wikipedia. It has limited accuracy , but when I used one over 60 years ago it worked easily. – blacksmith37 Jul 16 '22 at 21:17
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    I bought one[PTH-9 Serie] works fine, very responsive, battery life is poor tho. There must be continuous air flow thru the meter for accurate results. If you are measuring CO2 uptake or emission over time a continuous flow system seems needed. – jimchmst Jul 17 '22 at 01:46
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    Please update your question. What accuracy do you need, what CO2 range do you expect? – Karl Jul 17 '22 at 10:22
  • I think it has actually been answered. How do I close the question when the best answer is in a comment? – Henry Stone Jul 18 '22 at 20:22

1 Answers1

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You may determine the amount of $\ce{CO2}$ in air by using a saturated solution of calcium hydroxide $\ce{Ca(OH)2}$ ($\pu{0.0234 M}$ at $\pu{20°C}$). If you take $\pu{25 mL}$ of this solution and titrate it with $\ce{HCl 0.05 M}$ and thymolphtalein as indicator, you will need $\ce{23.38 mL HCl}$.

Now if you put $\pu{50 mL}$ of the same calcium hydroxide in a $5$ liters flask, close it and stir for half an hour, part of the calcium hydroxide will react accordingly to $$\ce{Ca(OH)2 + CO2 -> CaCO3(s) + H2O}$$ So the solution gets turbid. Titration of $\pu{25 mL}$ of the obtained solution with the same $\ce{HCl}$ solution will give you less than $\ce{23.38 mL}$, as $\ce{CaCO3}$ will not be destroyed by $\ce{HCl}$ if the indicator is thymolphtalein ($p\pu{Ka = 10}$). So the difference between the two volumes of $\ce{HCl}$ gives you the amount of $\ce{CO2}$ in the air of the big bottle.

Maurice
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