A buffer of pH 9.24 is to be prepared from a weak acid and its salt....

Question

Question

A buffer of pH 9.24 is to be prepared from a weak acid and its salt. The best acid from which to prepare the buffer is

(a) phthalic acid, K1 = 1.3 x 10-3 (1st ionization)

(b) hydrohen phthalate, K2 = 3.9 x 10-5

(c) arsenious acid, Ka = 6 x 10-10

(d) formic acid, Ka = 1.8 x 10-5

(e) phenol, Ka = 1.3 x 10-10

Please explain all options.

Answer 1

Answer #1

Answer should be (c)

buffer works best when concentration of acid and salt are equal

pH = pKa + log[Salt]/[Acid]

If [Salt]/[Acid] = 1 then log[Salt]/[Acid] = 0

pH = pKa

for Arsenic acid pKa = 9.22

very close to actual pH needed = 9.24

If you compare others then pH of Phenol will come 2nd closest.

Answer 2

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