# Is carbon dioxide soluble in petroleum ether, and why?

I googled it, and I'm finding some forum posts that say no, but no authoritative reference. CO2 is somewhat soluble in water (1.7 g/L at 20°C) and I understand that it's mostly NOT because it forms carbonic acid: it's just dissolved CO2 molecules. Why wouldn't the same thing happen in petroleum ether? Has anyone tried putting petroleum ether in a SodaStream device?

• Carbon dioxide is a dipole so it would made perfect sense to be soluble in water.Petroleum ether is again a polar molecule so why not? – Bright Future Sep 21 at 13:02
• mm petroleum ether is not polar is made of aliphatic compounds and carbon dioxide has dipole 0 – G M Sep 21 at 13:40
• While most of CO2 absorbed by water stays this way, the reaction is still driving the dissolution equilibrium forward, especially in high pH. – Mithoron Sep 21 at 14:40
• Carbone dioxide has zero dipole, but it's 2 bonds do not. They are polar and attracted to water. Dissociation of carbonic acid plays very minor role here. – Poutnik Sep 22 at 5:41
• @Mithoron ..but not for low pH of water with dissolved CO2. 1 atm CO2 leads to pH cca 3.9, the true pKa1 of H2CO3 is 3.6, so bicarbonates makes just few 0.x% of total CO2 content. – Poutnik Sep 22 at 6:30

Carbon dioxide is, in fact, more soluble in nonpolar solvents than in water.

From the Wikipedia page on carbon dioxide: Solubility in water 1.45 g/L at 25 °C (77 °F), 100 kPa (Alternative source: CRC handbook. Solubility is about twice as much at 0°C.)

From IUPAC, Solubility Data Series: Carbon Dioxide in Non-Aqueous Solvents at Pressures Less Than 200 kPa, chart on page 3: mole fraction of CO2 in hexane at 101.3 kPa, 300 K = 0.012, which corresponds to 4 g/L. (Solubility is only slightly (10-20%) higher at 0°C.)

So the forum posts I read were wrong.

As to why, I suppose it's sufficient to argue that CO2 is a nonpolar molecule, and like dissolves like.
(It's true because it's Latin: Similia similibus solvuntur! 😝)

• Nitrogen is non polar molecule as well, and that is the reason it's solubility in water is 2 orders lower than for CO2 :-) – Poutnik Sep 26 at 15:23
• It is rather the CO2 bond polarity does not manifest in non polar solvents, where the dominance has zero dipole moment. Similis similibus solvuntur as Well. :-) – Poutnik Sep 26 at 15:41

While $$\ce{CO2}$$ as a symmetric molecule has zero dipole moment, its 2 $$\ce{C=O}$$ bands do have dipole moment and are polar.

Polar water molecules interact with the polar bonds what decreases $$\ce{CO2(aq)}$$ chemical potential and raises solubility of $$\ce{CO2}$$ some 2 orders above solubility of $$\ce{O2}$$ or $$\ce{N2}$$.

That does not happen in non polar solvents likes alkanes of petroether.

BTW, why would anybody put petroether in a soda stream ??

• I'd like you to put petroleum ether in a Sodastream so you could tell me if you get fizzy petroleum ether of course! (It goes without saying that I won't do it myself.) – Martin Sep 22 at 18:42
• On a more serious note, do you have any actual data on the solubility of carbon dioxide in petroleum ether? Or maybe hexane? – Martin Sep 22 at 18:43
• This is behind a paywall pubs.acs.org/doi/pdf/10.1021/je0602972 – Poutnik Sep 22 at 18:59
• That's cool but the lowest pressure they consider is 17 bar - I'd like to know about atmospheric pressure. – Martin Sep 23 at 14:30
• @Martin ..proportionality.... 1/17 of 17 bar – Poutnik Sep 23 at 16:01