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 $ .



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