Why isn\'t the answer c)? I thought because there\'s a weak acid involved a stro

Question

Why isn't the answer c)? I thought because there's a weak acid involved a strong base would create a better buffer.

9. Ascorbic acid (HAsc) has a K, value of 8.0 x 10-5. An aqueous solution consisting of sodium ascorbate (NaAsc) and HAsc has a pH of 4.50. This solution a) would be equally capable of buffering against the addition of strong acid and strong base. (b would be better at buffering against the addition of strong acid than strong base. c) would be better at buffering against the addition of strong base than strong acid. (d) is not a buffer because ascorbic acid is a weak acid. (e) is not a buffer because ascorbate is a strong base.

Explanation / Answer

we need to know pKA value

pKa = -log(Ka)= -log(8*10^-5) = 4.096

then

pH = pKa + log(conjugate base / weak acid)

if pH = 4.50

then

4.50 = 4.096 +  log(conjugate base / weak acid)

10^(4.50 -4.096 ) = (conjugate base / weak acid)

(conjugate base / weak acid) = 2.5351

clearly, there is much more conjugate base than weak acid

therefore, it is much resistant agains H+ addition, since plenty of base will react with it,

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