I know this is probably an incredibly stupid question, but I'm making a hydrogen generator for a project. The basis of it is electrolysis of baking soda and water, which apparently gives off hydrogen, oxygen, and carbon dioxide. I want to separate these three gases into separate containers. Is this possible? Also, is baking soda and water the most efficient way of doing this?

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    $\begingroup$ It isn't easy. Gases don't naturally separate, though in electrolysis they do appear at different electrodes (oxygen on one, hydrogen on the other) so if you don't mix them you won't have to separate them. OTOH there are specialist membranes that will selectively allow hydrogen to diffuse through them and that works on a mixture. $\endgroup$ – matt_black Nov 14 '17 at 23:43
  • $\begingroup$ @matt_black I was thinking of something like that. Would it be possible to separate them using high voltage, so they would be attracted to either side? $\endgroup$ – HXGamer Nov 14 '17 at 23:58
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    $\begingroup$ If you're generating hydrogen and oxygen by electrolysis, the best solution is to just not let the gases mix in the first place. The two gases will be generated at different electrodes, so just trap the gases there. There is specialist glassware designed for this (e.g. this) but you can also just design something yourself. $\endgroup$ – chipbuster Nov 15 '17 at 3:03
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    $\begingroup$ SAFETY - You must also consider safety. A mixture of hydrogen and oxygen is explosive. $\endgroup$ – MaxW Nov 15 '17 at 7:47

To separate hydrogen, a warmed Pd membrane is very effective... except that Pd catalytically ignites the $\ce{H2 - O2}$ mixture. oops

A carbon nanotube membrane might work... but would be a bit pricey.

Various organic polymers have been used as hydrogen-permeable membranes, though some are poisoned by $\ce{CO2}$.

Actually, for a demonstration, $\ce{H2}$ is so much more mobile than the other gases that even a cellulose dialysis membrane might work to some extent, providing "enriched" hydrogen with some of the other gases still included.

The $\ce{CO2}$ could then be separated from oxygen by chilling. The melting point of $\ce{CO2}$ is ~217 K. Using a cooling bath of isopropanol and dry ice should get to ~195 K. It might be inefficient and redundant to use $\ce{CO2}$ to trap $\ce{CO2}$, but this would be acceptable for a demonstration, I assume.

An alternative is to compress the $\ce{CO2 - O2}$ mix until the $\ce{CO2}$ liquefies.


I would prefer using H2SO4 and Zn or Cu so that it produces H faster as Zn and Cu are highly reactive and the process with Cu looks beautiful to and helpful in checking wheather the reaction is happening as it turns blue and u can also explain crystallization.Seperating those gases need high level equipment and can be done be coolers,high pottemtial,pressure changeable equipments

  • $\begingroup$ Do you talk about electrolysis or the chemical reactions of Cu and Zn with sulfuric acid? In the first case the amount of hydrogen produced is determined by the current. In the latter case copper won't give you much hydrogen. $\endgroup$ – aventurin Apr 21 '18 at 19:14

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