Shovw all work (where appropriate) for full credit. You may use a separate sheet
ID: 636566 • Letter: S
Question
Shovw all work (where appropriate) for full credit. You may use a separate sheet but place your answer on this sheet and staple your work to it. A250 mL of a 0.0450 M aqueous solution of an organic acid, HA, was found to have a pH of 3.20. Determine the pK, of this organic acid. 1. 2. Aniline (mol. mass- 93.13 g/mol, density-1.0217 g/ml, mp -6.3 °C) is an important reagent for the synthesis of dyes such as indigo which is used to color "blue jeans". It is isolated from crude oil. In solution, aniline behaves as a weak base. Determine the Kb for aniline, if a solution prepared by dissolving 0.1863 g of aniline in enough water to prepare 250.0 ml of solution was found to have a pH of 8.418. Aniine overExplanation / Answer
1)
use:
pH = -log [H+]
3.2 = -log [H+]
[H+] = 6.31*10^-4 M
HA dissociates as:
HA -----> H+ + A-
4.5*10^-2 0 0
4.5*10^-2-x x x
Ka = [H+][A-]/[HA]
Ka = x*x/(c-x)
Ka = 6.31*10^-4*6.31*10^-4/(0.045-6.31*10^-4)
Ka = 8.973*10^-6
use:
pKa = -log Ka
= -log (8.973*10^-6)
= 5.05
Answer: 5.05
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