Using $p K_{a}$ values (acetic acid 4.76, benzoic acid 4.20, 2-nitrobenzoic acid 2.17, phenol 10.0, water 15.7), which of the following equilibria lies predominantly to the LEFT?

A $C X_{6} H X_{5} OH + CH X_{3} COO X^{-} C X_{6} H X_{5} O X^{-} + CH X_{3} COOH$
B $2 - O X_{2} N - C X_{6} H X_{4} - COOH + CH X_{3} COO X^{-} 2 - O X_{2} N - C X_{6} H X_{4} - COO X^{-} + CH X_{3} COOH$
C $C X_{6} H X_{5} COOH + OH X^{-} C X_{6} H X_{5} COO X^{-} + H X_{2} O$
D $C X_{6} H X_{5} O X^{-} + C X_{6} H X_{5} COOH C X_{6} H X_{5} OH + C X_{6} H X_{5} COO X^{-}$

Answer: A

Direction is set by

lo g K

p K_{a}

(conjugate acid of base)

-

p K_{a}

(acid): phenol/acetate

= 4.76 - 10.0 = - 5.24

(left); 2-nitrobenzoic acid/acetate

= 4.76 - 2.17 = 2.59

(right); benzoic acid/hydroxide

= 15.7 - 4.20 = 11.5

(right); benzoic acid/phenoxide

= 10.0 - 4.20 = 5.8

(right).