2018 11:55 PM 2.8/10 3/3/2018 05:04 PM Gra -Print ||Calculator Periodic Table n4

Question

2018 11:55 PM 2.8/10 3/3/2018 05:04 PM Gra -Print ||Calculator Periodic Table n4 of 9 Mapd What concentrations of acetic acid (pKa 4.76) and acetate would be required to prepare a 0.20 M buffer solution at pH 4.6? 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 tic acid), [A 2. Use the mole fraction of acetate to calculate the concentration of acetate. 3. Calculate the concentration of acetic acid. Step 1: Rearrange the Henderson Hasselbalch equation to solve for HA The Henderson-Hasselbaich equation is Use the Henderson-Hasselbalch equation to solve for if the solution is at pH 4.6 HA Number Enter your answer as a number. For example, 9.6 Do not enter a formula lke 10*2 HA] Previous Give Up & View Solution ) Check Answer ONet Ext. DOLL F1 F2 F3 F4 F5 F6 F7 F8 F9

Explanation / Answer

To prepare acetic acid/acetate (acid/base) buffer

pH = 4.6 for buffer

pKa = 4.76

concentration of buffer = 0.20 M

0.20 M = [acetic acid] + [acetate] -- (1)

Using Hendersen-Hasselbalck equation,

pH = pKa + log(base/acid)

4.6 = 4.76 + log([acetate]/[acetic acid])

[acetate] = 0.7[acetic acid]

feed in (1)

0.20 M = [acetic acid] + 0.7[acetic acid]

[acetic acid] concentration in buffer = 0.20 M/1.7 = 0.12 M

[acetate] concentration in buffer = 0.20 - 0.12 = 0.08 M

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