Homework Help: Org. Chem.

Posted by Chelsea on Monday, September 14, 2009 at 2:05am.

Explain the results in terms of polarities and/or hydrogen bonding.

- water and ethyl alcohol= miscible
water is highly polar and ethyl alcohol has intermediate polarity.

- water and diethyl ether= immiscible
water is highly polar and diethyl ether is only slightly polar

- water and methylene chloride= immiscible
water is highly polar and methylene chloride is what?

- water and hexane= immiscible
water is highly polar and hexane is nonpolar

- hexane and methylene chloride= miscible
hexane is nonpolar and methylene chloride is ? nonpolar?

Are these correct? Also, if you can add any info. on the polarities or include hydrogen bonding in the explanation please do.

Org. Chem. - Dr Russ, Monday, September 14, 2009 at 5:05am
It is not that easy to do these predictions just based on polarity. You need to consider the molecule's ability to hydrogen bond (i.e. is it hydrophylic?) or contains a large hydrocarbon part which makes it hydrophobic.

If we start with the alcohols, the short chain alcohols (methanol and ethanol) are miscible with water as the OH can hydrogen bond with water molecules. In addition the small hydrocarbon part makes them very much less hydrophobic than a molecule with a longer hydrocarbon chain. As the chain length increases the molecule becomes more hyrdophobic and the solubility in water decreases.

A similar effect is seen with the ethers. Dimethyether is soluble in water whereas diethyl ether with more hydrocarbon is much less soluble 'immiscible' although there is an appreciable solubility in water.

The chlorinated compounds chloromethane through to carbontetrachloride are polar organic molecules, but because they cannot hydrogen bond with water are immiscible with water, i.e. are hydrophobic.

Does this help?
Org. Chem. - Chelsea, Monday, September 14, 2009 at 11:04am
Somewhat, but still a little confused about the individual cases. Thanks though.
Org. Chem. - katrina, Wednesday, May 18, 2011 at 3:31pm
why is water and tetrachloride immiscible

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