How do I measure the percentage of CO2 in the air? [closed]








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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?




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.


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