What concentrations of acetic acid (pKa = 4.76) and acetate would be required to

Question

What concentrations of acetic acid (pKa = 4.76) and acetate would be required to prepare a 0.20 M buffer solution at pH 4.9? Note that the concentration and/or pH value may differ from that in the first question. STRATEGY 1. Rearrange the Henderson-Hasselbalch equation to solve for the ratio of base (acetate) to acid (acetic acid), [AVHA 2. Use the mole fraction of acetate to calculate the concentration of acetate. 3. Calculate the concentration of acetic acid. That is, there are 1.4 molecules of acetate for each molecule of acetic acid. acetate Step 1: The ratio of base to acid is = 1.4 acetic acid Step 2: Use the mole fraction of acetate to calculate the concentration of acetate. Number acetate

Explanation / Answer

Preparation of buffer

weak acid/conjugate base = [acetic acid]/[acetate]

Using Hendersen-Hasselbalck equation,

pH = pKa + log(conjugate base/weak acid)

needed pH = 4.9

pKa = 4.76

So,

4.9 = 4.76 + log([acetate]/[acetic acid])

[acetate] = 1.4[acetic acid]

we know,

[acetic acid] + [acetate] = 0.2 M

[acetic acid] + 1.4[acetic acid] = 0.2 M

[acetic acid] concentration in the buffer = 0.2 M/2.4 = 0.083 M

[acetate] concentration in the buffer = 0.2 - 0.083 = 0.117 M

Related Questions

Navigate

• Browse (All)
• Browse W
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.