You wish to prepare an HC₂H₃O₂ buffer with a pH of 4.14.If the pK_a of is 4.74,what ratio of C₂H₃O₂^-/HC₂H₃O₂ must you use? A) 0.10 B) 0.60 C) 0.25 D) 3.98 E) 6.0

Question

Quizplus · Accepted Answer

First, we need to use the Henderson-Hasselbalch equation to find the ratio of the conjugate base and acid to the salt:

pH = pK + log([A-]/[HA])

4.14 = 4.74 + log([C12H23NaO2]/[C12H24O2])

-0.60 = log([C12H23NaO2]/[C12H24O2])

[C12H23NaO2]/[C12H24O2] = 0.25

Therefore, we need to use a ratio of 1:4 of the conjugate base to acid to the salt:

[C12H23NaO2] / [C12H24O2] = 1/4
[H3O+] = 10^-4.14 = 6.76 x 10^-5 M

Note: the answer choices D and E are not valid ratios as they are greater than one.

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