Weak Acids and Bases 12.53

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Semi Yoon
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Weak Acids and Bases 12.53

Postby Semi Yoon » Sat Dec 01, 2018 4:18 pm

Why do these acids have different strengths? (a) acetic acid and trichloroacetic acid; (b) acetic acid and formic acid.

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Re: Weak Acids and Bases 12.53

Postby Sean_Rodriguez_1J » Sun Dec 02, 2018 12:29 pm

For a), trichloroacetic acid has a -CCl3 group that is bonded to a carboxyl group. That -CCl3 group can attract electrons more effectively than the CH3 group in acetic acid (Chlorine is far more electronegative than carbon and creates a polar bond, whereas the C-H bond in CH3 is non-polar), making it a better lone pair acceptor and consequently a stronger acid.
For b), the CH3 group present in acetic acid (CH3COOH) will donate its electrons (the lone pair on the carbon atom) to attach to the carboxyl group, making it less electron withdrawing than the H atom bonded to COOH in formic acid. Therefore, formic acid is a stronger acid than acetic acid (as a side note, trichloroacetic acid is much stronger than either of these two acids).

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