What molar ratio of acetic acid to sodium acetate is required to create a buffer solution having a pH of 4.88 at 25°C? K_a for HC₂H₃O₂ is 1.8 × 10^-5.

Question

Quizplus · Accepted Answer

The Henderson-Hasselbalch equation, pH = pKa + log([A-]/[HA]), is used to find the molar ratio of acetic acid ([HA]) to sodium acetate ([A-]) required for a buffer solution. Given that the pH is 4.88 and the pKa (derived from the given Ka = 1.8 × 10^-5) is -log(1.8 × 10^-5) ≈ 4.74, we can rearrange the equation to solve for the ratio [A-]/[HA]. Plugging in the values, 4.88 = 4.74 + log([A-]/[HA]), we find that log([A-]/[HA]) = 0.14. Converting from log form, [A-]/[HA] = 10^0.14 ≈ 1.38, which rounds to approximately 1.4, but since the question asks for the ratio of acetic acid to sodium acetate, the inverse is needed, which is 1/1.4 ≈ 0.73.

What Molar Ratio of Acetic Acid to Sodium Acetate Is