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Why are alkanes insoluble in water?

hi,
Can someone please explain to me why the alkanes are insolube in water? I'm thinking that the alkanes have london forces and so does water, so they dissolve. Is this wrong?
Thanks, Kinglee
Because an alkane is non-polar it has no dipole-dipole interactions it can't be soluble in water which is a polar solvent.

It is soluble in non-polar solvents though
Reply 2
Avatar for _NMcC_
_NMcC_
15
Original post by kinglee
hi,
Can someone please explain to me why the alkanes are insolube in water? I'm thinking that the alkanes have london forces and so does water, so they dissolve. Is this wrong?
Thanks, Kinglee


Water has hydrogen bonds, alkanes have London Forces, which go under Van Der Waals 'category'.

Another way to think about it is that alkanes are non-polar and water molecules are polar (because it has a permanent dipole moment, so alkanes won't dissolve because they only have induced dipole-dipole moments (Van der waals). You could dissolve alkanes in another non-polar solvent like Diethyl Ether or Chloroform to name a few. Alkanes themselves can be used as non-polar solvents.

There are actually two types of polar solvents, polar protic and polar aprotic. The reason this distinction is made is because certain reactions can actually be affected by if a solvent is protic or aprotic (e.g Sn2) but that's for another day.

A quick way to think about it ( like if you were in a lab, trying to decide on a solvent) is 'Like dissolves like', polar dissolves polar, non-polar dissolves non-polar. Often though you would need to think deeper and factor in things like boiling points depending on what you are doing e.g Crystallisation.
(edited 6 years ago)
Reply 3
Avatar for ImBear
ImBear
9
Alkenes are Non Polar (There are no charged atoms) as water is a polar solvent it dissolves polar molecules, oxygen pulls away the + atom and hydrogen pulls the negative atom away, separating the molecule, think of NaCl, or Na+ and Cl-, this is soluble. This means Alkenes and Alkanes are insoluble in water.
Reply 4
Avatar for kinglee
kinglee
OP
7
oh ok I understand now, thanks for replying guys,
King Lee

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