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Chapter 16: Problem 12

Calculate the \(\mathrm{pH}\) of the following two buffer solutions: (a) \(2.0 \mathrm{M} \mathrm{CH}_{3} \mathrm{COONa} / 2.0 \mathrm{M} \mathrm{CH}_{3} \mathrm{COOH}\), (b) \(0.20 \mathrm{M} \mathrm{CH}_{3} \mathrm{COONa} / 0.20 \mathrm{M} \mathrm{CH}_{3} \mathrm{COOH} .\) Which is the more effective buffer? Why?

Short Answer

Expert verified
The pH of both buffer solutions (a) and (b) is 4.74. However, buffer solution (a) is more effective due to its higher concentrations of the acidic and basic components.

Step by step solution

01

Calculate pH for Buffer Solution (a)

Utilize the Henderson-Hasselbalch equation which allows the pH to be calculated for a buffer solution: pH = pKa + log([A-]/[HA]). Here, [A-] represents the concentration of the base (CH3COONa) and [HA] represents the concentration of the acid (CH3COOH). Looking on the periodic table, the pKa for CH3COOH is 4.74. Therefore, for (a) pH = 4.74 + log(2.0/2.0) = 4.74.
02

Calculate pH for Buffer Solution (b)

For buffer solution (b), we use the same Henderson-Hasselbalch equation. The pH is thus 4.74 + log(0.20/0.20) = 4.74.
03

Determine the More Effective Buffer

In order to make this determination, it's necessary to understand that a more effective buffer has greater buffering capacity, i.e., it can neutralize more acid or base without changing the pH significantly. Buffer capacity is proportional to the concentrations of [HA] and [A-]. Hence, since the concentrations of [HA] and [A-] in (a) are larger than that in (b), (a) is the more effective buffer.

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