Question

A physician wishes to prepare a buffer solution at $pH=3.85$ that efficiently resists change in at $pH=3.85$ that efficiently resists change 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?

• A. 2, 5-Dihydroxy benzoic acid $({pK}_a=2.97)$
• B. Acetoacetic acid $({pK}_a=3.58)$
• C. m-Chlorobenzoic acid $({pK}_a=3.98)$
• D. p-Chlorocinnamic acid $({pK}_a=4.41)$

Answer 1

Answer: (A)

2, 5-Dihydroxy benzoic acid $({pK}_a=2.97)$

$2,5-Dihydroxybenzoic$ $acid$ $p{K}_a=2.97$

$pH=p{K}_a+\log \frac{\left[salt\right]}{\left[acid\right]}$ for small concentration of buffering agent & for maximum buffer capacity $\frac{\left[Salt\right]}{\left[Acid\right]}\simeq 1$