First slide

Buffer Capacity

Question

A physician wishes to prepare a buffer solution at pH = 3. 58 that efficiently resists a change in pH yet contains only small conc. of the buffering agents. Which one of the following weak acid together with its sodium salt would be best to use?

Easy

A

m-chloro benzoic acid (pK_a = 3.98)
B

p - chlorocinnamic acid (pK_a = 4.41)
C

2.5 - dihydroxy benzoic acid (pK_a = 2.97)
D

Acetoacetic acid (pK_a = 3.58)

Solution

Given that the buffer solution contains only small concentraiton of buffering agents
$\Rightarrow log\frac{[salt]}{[acid]}=0$
$P^H=P^{K_a}+log\frac{[salt]}{[acid]}\;\cong\;P^{K_a}=3.58$

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