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MCAT Question A Day - 4/3/13 - Answer!

Oils are liquids because they

A.  contain cis-unsaturated acid chains that do not fit well together.
B.  contain saturated acid chains that fit together well due to tetrahedral bond angles.
C.  undergo hydrogenation.
D.  have high melting points.

The correct answer is (A). Fats are all glycerides, composed of glycerol and carboxylic acids.
These fatty acids are both saturated and unsaturated, the latter exhibiting mostly cis configurations
about the double bonds. Fats with mostly saturated fatty acids have higher melting points
because the tetrahedral carbons fit more tightly together than the cis fatty acid chains, making
for stronger intermolecular forces. Oils or liquid fats have high numbers of unsaturated fatty
acid chains that conversely cause lower melting points.