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Chapter 17: Problem 8

Calculate the \(\mathrm{pH}\) of these two buffer solutions: (a) \(2.0 \mathrm{M} \mathrm{CH}_{3} \mathrm{COONa} / 2.0 \mathrm{MCH}_{3} \mathrm{COOH}\), (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 the given buffers is 4.74. The more effective buffer is buffer a (2.0 M CH3COONa / 2.0 MCH3COOH), as it has higher concentrations of buffer components and therefore a higher buffer capacity.

Step by step solution

01

Calculate the pH

The \(pKa\) of acetic acid (\(CH3COOH\)) is 4.74. Given that both the concentrations of acetic acid and sodium acetate in each buffer are equal, we can simplify the Henderson-Hasselbalch equation to \(pH = pKa\), because the \(\log \frac{[A-]}{[HA]}\) term becomes \(\log(1)\) which is 0. Hence, \(pH = 4.74\) for both buffers.
02

Determine The Buffer Effectiveness

The effectiveness of the buffers can be inferred by the buffer capacity, which is the amount of acid or base a buffer can neutralize before the pH starts to change significantly. The buffer capacity depends on the absolute concentrations of acid and base in the buffer solution. Hence, the \(2.0 M CH3COONa / 2.0 MCH3COOH\) buffer solution (buffer a) can neutralize more added acid or base than the \(0.20 M CH3COONa / 0.20 M CH3COOH\) buffer (buffer b), because buffer a has higher concentrations of buffer components. Thus, buffer a is more effective.

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Most popular questions from this chapter

A sample of \(0.1276 \mathrm{~g}\) of an unknown monoprotic acid was dissolved in \(25.0 \mathrm{~mL}\) of water and titrated with \(0.0633 \mathrm{M} \mathrm{NaOH}\) solution. The volume of base required to reach the equivalence point was \(18.4 \mathrm{~mL}\). (a) Calculate the molar mass of the acid. (b) After \(10.0 \mathrm{~mL}\) of base had been added to the titration, the \(\mathrm{pH}\) was determined to be 5.87 . What is the \(K_{\mathrm{a}}\) of the unknown acid?

A 1.0 -L saturated silver carbonate solution at \(5^{\circ} \mathrm{C}\) is treated with enough hydrochloric acid to decompose the compound. The carbon dioxide generated is collected in a \(19-\mathrm{mL}\) vial and exerts a pressure of \(114 \mathrm{mmHg}\) at \(25^{\circ} \mathrm{C}\). What is the \(K_{\mathrm{sp}}\) of \(\mathrm{Ag}_{2} \mathrm{CO}_{3}\) at \(5^{\circ} \mathrm{C} ?\)

Calculate the \(\mathrm{pH}\) of the \(0.20 \mathrm{M} \mathrm{NH}_{3} / 0.20 \mathrm{M} \mathrm{NH}_{4} \mathrm{Cl}\) buffer. What is the \(\mathrm{pH}\) of the buffer after the addition of \(10.0 \mathrm{~mL}\) of \(0.10 \mathrm{M} \mathrm{HCl}\) to \(65.0 \mathrm{~mL}\) of the buffer?

The \(\mathrm{p} K_{\mathrm{a}} \mathrm{s}\) of two monoprotic acids \(\mathrm{HA}\) and \(\mathrm{HB}\) are 5.9 and \(8.1,\) respectively. Which of the two is the stronger acid?

Specify which of these systems can be classified as a buffer system: (a) \(\mathrm{KNO}_{2} / \mathrm{HNO}_{2}\) (b) \(\mathrm{KHSO}_{4} / \mathrm{H}_{2} \mathrm{SO}_{4}\) (c) HCOOK/HCOOH.
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