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Thu 7 Jul, 2005 08:16 pm
Water is called extremely polar and a universal solvent because its hydrogen electrons spend more time near the oxygen nucleus than their own.
Is there a nonpolar compound that has the same "universal" distinction in dissolving other nonpolar compounds?
I know aromatic hydrocarbons are examples of nonpolar compounds, and that benzene is common as a solvent in particular. But are there degrees of nonpolarity, distinguishing one liquid as the most nonpolar? Or are all nonpolar compounds equally nonpolar?
Another way of asking my question would be, does nonpolar imply no such interatomic electron deviation or only very little?
Also, what does symmetry/molecular geometry tell you about polarity?
In organic chemistry I always used as a rule of thumb, non-polar materials dissolved in non-polar solvents and polar materials in polar solvents.
Since salts were very polar, they needed a very polar solvent and paraffine was very non-polar so it needed a nonpolar solvent. And polarity of a solvent was more of a function of availability of hydronium (OH-). So water was very polar, so was ammonia. Methanol (CH3OH) was pretty polar but not so much as water, ethanol (C2H5OH) had some features of both polar with the OH end and non-polar with the CH3CH2 end. If you wanted aromatic solvents, Benzene was non-polar, Toluene had a non-polar spot, and Aniline was somewhere in the middle. For straight aliphatic materials carbon tetrachloride was very nonpolar (and carcinogenic). I haven't discussed petroleum distillates (nonpolar), acetone (also nonpolar with a polar oxygen), Stoddard's solvent (an industrial mixture) and ethers (kinda like acetone but not so much), and the benefits of detergents and soaps with their polar and non-polar ends.
I guess the best rule for dissolution was that 'like tends too dissolve like.'
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