A buffer solution is prepared by placing twice the concentration of propanoic acid (C₂H₅COOH,K_a=1.34 ×10⁻⁵)as the concentration of its conjugate base sodium propanoate into a flask.The pH of the resulting buffer solution is best described as which of the following?

Question

Quizplus · Accepted Answer

The pH of the buffer can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the conjugate base and [HA] is the concentration of the acid. Given that the concentration of the acid is twice that of its conjugate base, the ratio [A-]/[HA] is 1/2. The pKa of propanoic acid is -log(1.34 × 10^-5) = 4.87. Substituting into the equation gives pH = 4.87 + log(1/2), which results in a pH less than 4.87 because log(1/2) is negative.

A Buffer Solution Is Prepared by Placing Twice the Concentration