Explain the preparation of an acidic buffer solution with an example.

(N/A) An acidic buffer solution is prepared by mixing a weak acid $(HA)$ and its salt with a strong base $(A^-)$.
The $pH$ of the solution is determined by the Henderson-Hasselbalch equation:
$pH = pK_{a} + \log \frac{[Salt]}{[Acid]}$
If the concentration of the weak acid and its conjugate base (salt) are equal,i.e.,$[HA] = [A^-]$,then:
$pH = pK_{a} + \log(1) = pK_{a} + 0 = pK_{a}$.
Therefore,to prepare a buffer with a desired $pH$,one should select a weak acid whose $pK_{a}$ value is close to the target $pH$.
Example: Acetic acid $(CH_3COOH)$ has a $pK_{a}$ of $4.76$. $A$ buffer solution prepared by mixing equimolar concentrations of acetic acid and sodium acetate $(CH_3COONa)$ will have a $pH$ approximately equal to $4.76$.