# How do we separate H2O from CO2? [closed]

Let's say I have a mixture of $$\ce{CO2}$$ and $$\ce{H2O}$$ gases. I've read that $$\ce{CO2}$$ is heavier (molar mass is $$\pu{44.01 g/mol}$$) than $$\ce{H2O}$$ (molar mass is $$\pu{18.02 g/mol}$$). So, if the mixture is supplied to a cylinder from the bottom, will only the water vapour reach the top? If so, is this a good way to separate the $$\ce{CO2}$$ and water vapour? Or is there a more efficient way to separate them?

• Convenient reference for text/formula formatting: Notation basics / Formatting of math/chem expressions / upright vs italic // For more: Math SE MathJax tutorial. // Not to be applied in CH SE titles. Nov 29, 2022 at 14:33
• What you propose does not work at all. Never.
– Karl
Nov 29, 2022 at 19:38
• @Karl Then, could you please write an answer for a better solution to this problem? Nov 30, 2022 at 7:14
• It is hard to see any source containing a mixture of CO2 and water as gasses. Most likely under normal conditions you would have water liquid under an atmosphere of carbon dioxide (with the water saturated with CO2). Or a stream of hot gases containing both. What circumstances are you considering? Nov 30, 2022 at 14:34

Separation of $$\ce{H2O}$$ from $$\ce{CO2}$$ has been done by all analytical chemists in the $$19$$th century, when they had to determine the formula of a new organic compound X. The compound X was mixed with some $$\ce{CuO}$$ powder, introduced in a horizontal glass tube and heated by a burner in an oxygen current. X was burned int $$\ce{CO2}$$ and $$\ce{H2O}$$. Then the oxygen gas current containing some $$\ce{H2O}$$ and $$\ce{CO2}$$ had to cross another glass tube filled with pieces of anhydrous calcium chloride $$\ce{CaCl2}$$ which fixed the water vapor, producing $$\ce{CaCl2·6H2O}$$. The $$\ce{CaCl2}$$ tube was weighed before and after the operation. The increase in weight gives the total amount of $$\ce{H2O}$$ in the mixture of gases.
Then the gas was sent to bubble through a concentrated $$\ce{NaOH}$$ solution, where the following reaction happened $$\ce{CO2 + 2 NaOH -> Na2CO3 + H2O}$$ The $$\ce{NaOH}$$ solution was weighed before and after the operation. The increase in weight gives the total amount of $$\ce{CO2}$$ in the gas.