# Buffer solution [closed]

Prepare an aqueous buffer solution of $\mathrm{pH}=2.85$ that efficiently resists a change in pH yet contains only a small amount of buffering agent. Which one of the following weak acid together with its salt would be best to use?

A) m-chlorobenzoic acid ($\mathrm{p}K_a=3.98$)

B) p-chloro cinnamic acid ($\mathrm{p}K_a=4.41$)

C) 2,5-dihydroxy benzoic acid ($\mathrm{p}K_a=2.97$)

D) Acetoacetic acid ($\mathrm{p}K_a=3.58$)

Looking at the $\mathrm{p}K_a$ values C) is the strongest acid. However I cannot get if the strongest acid is best suited for buffer action which resists change in pH when small amounts of acid and base are added to it.

• When $pH$ moves away from $pK_a$ value the concentration of acid and salt vary more.But I couldn't get how this distribution matters for making the best buffer?Thanks. – user471651 Nov 8 '17 at 8:30