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So I understand $\ce{CH4}$ has a low solubility, but when it does dissolve, what does it form? E.g. $\ce{HCl_{(g)} + H2O -> H3O+_{(aq)} + Cl^{-}_{(aq)}}$. So what does $\ce{CH4 + H2O}$ form?

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  • $\begingroup$ Why do you think it would react with water? Generally gases with low solubility in water don't react with it - methane is very, very weak acid and base - it's like opposite of HCl $\endgroup$ – Mithoron Jan 13 '15 at 21:43
  • $\begingroup$ It's not a chemical reaction per se, other than minor hydrogen bonding. It's more like games with ball bearings that fit into depressions when tilted just right. $\endgroup$ – DrMoishe Pippik Jan 13 '15 at 23:51
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Methane dissolved in water is simply methane. It does not react with the water under normal conditions.

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    $\begingroup$ There will of course be hydrogen bonding. $\endgroup$ – Martin - マーチン Jan 14 '15 at 13:58
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    $\begingroup$ Hydrogen bonding is unlikely to be significant as the C-H bond in methane is virtually apolar. There's very little H-bonding even for the ammonium ion in water. $\endgroup$ – J. LS Jan 14 '15 at 15:18
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I think you are confusing dissociation with dissolution. Bonds do not need to be broken in order to dissolve a substance. The reason so many covalent compounds do disassociate in water is that water is a highly polar solvent and therefore preferentially solvates ions (provides the driving force for the disassociation).

Methane is pratically insoluble in water, but it will dissolve at low enough concentration to give a solution of methane in water, with only van der Waals forces between the methane and water molecules.

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  • $\begingroup$ Solvent-solvent interactions must be disrupted in the process of dissolution. $\endgroup$ – Dissenter Jan 14 '15 at 16:58
  • $\begingroup$ Yes. The solubility of methane in water is 22.7 mg per litre; there are compounds which are actually insoluble for that reason. $\endgroup$ – J. LS Jan 14 '15 at 17:48
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A clathrate compound is like a cage. It relies on lattice spacing much more than molecular attraction to stick together; see http://en.wikipedia.org/wiki/Clathrate_compound. Methane-water ice clathrate is comparatively stable almost to the melting point of ice, and there are huge amounts under the oceans and in Arctic permafrost;see http://en.wikipedia.org/wiki/Methane_clathrate.

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    $\begingroup$ I think you should make some refercence to the question - clathrates aren't typical solution. $\endgroup$ – Mithoron Jan 13 '15 at 21:47
  • $\begingroup$ clathrates are not solutions of methane in water $\endgroup$ – bon Jan 14 '15 at 11:39
  • $\begingroup$ @Mithoron Methane clatrate is a terminal point, it is an idealised structure of a solution of methane in water at highest possible concentration, and it is X-Rayable, so a direct evidence of structure is available. Besides, OP have not clarified directly if he is talking about liquid or solid water =) (OK, it's a bit of stretch, but still). $\endgroup$ – permeakra Jan 14 '15 at 13:27
  • $\begingroup$ Yeah, so I say "typical" :D $\endgroup$ – Mithoron Jan 14 '15 at 13:29

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