Chemical Bonding Worksheets Page 22
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22"Like dissolves like" rule:
– Polar substances will dissolve in or mix with other polar substances.
– Nonpolar substances will dissolve in mix other nonpolar substances.
– But polar and nonpolar substances don’t mix or dissolve in one another.
Consider the images below:
(a) Two nonpolar liquids, CCl
(l) and octane (C
H
) in gasoline, will mix.
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8
18
(b) Polar water molecules do not mix with nonpolar gasoline/octane molecules
but instead remain in separate layers.
Note: Hydrocarbons are compounds that contain only carbon and hydrogen (e.g. C
H
).
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– The symmetrical shape of hydrocarbons results in the dipoles for each C-H bond
in the molecule always cancelling—e.g. just like in CH
.
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→ Hydrocarbons are always nonpolar .
Ex. 1: a. Draw the Lewis structure for methanol (CH
OH) using the skeleton structure below,
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then sketch the 3D shape with dipoles:
Lewis structure
3D shape with dipoles
H
H
C
O
H
H
b. Is methanol polar or nonpolar?
Polar
Nonpolar
Thus, any alcohol (a molecule with a hydroxyl group − OH ) is polar ,
so liquid alcohols will mix with and solid alcohols will dissolve in water.
CHEM 121 Tro Chapter 10 F2012
page 22 of 22
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