Equilibrium Question 455
Question: A physician wishes to prepare a buffer solution at $ pH=3.58 $ that efficiently resists changes in $ pH $ yet contains only small concentration of the buffering agents. Which of the following weak acids together with its sodium salt would be best to use [CBSE PMT 1997]
Options:
A) $ m- $ chlorobenzoic 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) $
Show Answer
Answer:
Correct Answer: C
Solution:
$ pH=pK_{a}+log\frac{[\text{ Salt }]}{[\text{ Acid }]} $ . For small concentration of buffering agent and for maximum buffer capacity $ \frac{[\text{ Salt }]}{[\text{ Acid }]}\approx 1 $ .
