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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: ocarina_noob on March 21, 2013, 07:05:10 pm

Title: quick question
Post by: ocarina_noob on March 21, 2013, 07:05:10 pm

Dichloromethane is polar but not very soluble in water- why is that
?

Title: Re: quick question
Post by: lzxnl on March 21, 2013, 10:40:24 pm

Remember, just because something is polar doesn't mean it will be soluble in water. If it forms stronger bonds with itself, it won't dissolve in water. When a substance dissolves, there are several bonds that have to be broken: solvent-solvent bonds, such as the water H-bonds, and the solute-solute bonds.
Now the electronegativity difference between carbon and chlorine is merely 0.5, so the bonds aren't terribly polar. Also, chlorine is a relatively large atom, unlike oxygen, nitrogen and fluorine, so hydrogen bonding does not occur with it. Therefore, the bonds that dichloromethane may form with water are much weaker than the hydrogen bonding between water molecules and so the process would not be favourable energetically.