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I heard dichloromethane is soluble in water 1:50, but I also heard it is not because it can't form hydrogen bonds. I'm confused. Is there a way to extract it? Would putting the water to $40~\mathrm{^\circ C}$ make it evaporate trough water?

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  • $\begingroup$ 1:50 is misleading. Wikipedia gives dichloromethane’s solubility in water as $20\,\mathrm{\frac{g}{l}}$ which is approximately 1:50 w/w, but ratios are usually understood v/v. (weight/weight versus volume/volume) $\endgroup$ – Jan Sep 30 '15 at 9:57
  • $\begingroup$ @Jan That's a good start for an answer... $\endgroup$ – Martin - マーチン Sep 30 '15 at 11:11
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    $\begingroup$ "it is not because it can't form hydrogen bonds" - Just bear in mind that solubility isn't a black and white thing. Dichloromethane is pretty insoluble in water (as opposed to something like ethanol) because it doesn't H-bond with water, but that doesn't mean it is entirely insoluble. $\endgroup$ – orthocresol Sep 30 '15 at 12:39
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The solubility of dichloromethane in water (as well as the solubility of water in dichloromethane) depends on temperature. At a temperature of $T=20\ \mathrm{^\circ C}$, the solubility amounts to $17.6\ \mathrm g$ dichloromethane per $1\ \mathrm{kg}$ water; i.e. the mass fraction of dichloromethane is $w_{\ce{C2H2Cl2}}=0.0173$ or $w_{\ce{C2H2Cl2}}=1.73\,\%$. [source: “Aqueous Solubility and Henry’s Law Constants of Organic Compounds”, in CRC Handbook of Chemistry and Physics, 90th Edition (CD-ROM Version 2010), David R. Lide, ed., CRC Press/Taylor and Francis, Boca Raton, FL.]
(See here for values at other temperatures.)

You cannot simply evaporate pure dichloromethane (boiling point: $40\ \mathrm{^\circ C}$) from such mixtures since dichloromethane and water form an azeotrope, which boils at $38.8\ \mathrm{^\circ C}$. The mass fraction of water in this azeotrope is about $w_{\ce{H2O}}=1\,\%$.

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    $\begingroup$ You could fractionally distil the mixture until the distillate no longer contains dichloromethane. The remaining water in the distillation flask would then be free of dichloromethane. $\endgroup$ – iad22agp Sep 30 '15 at 14:16
  • $\begingroup$ Is this mean at 40C i will evaporate the azeotrope wich have 1% water in it ? I have no interest in pure DCM, I want DCM-Free water. $\endgroup$ – simon Oct 4 '15 at 4:48
  • $\begingroup$ @simon - yes. Even if your lose some water in getting the DCM off, you'll be left with what you want. $\endgroup$ – Beerhunter Nov 26 '15 at 0:01

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