# Chm 2

Consider the following weak acids and their Ka values

Acetic acid Ka = 1.8x10^-5
Phosphoric acid Ka = 7.5x10^-3
Hypochlorous acid Ka = 3.5x10^-8

What weak acid-conjugate base buffer system from the acids listed is the best chouce to prepare the following bufers?: Explain your reasoning.

(a) pH 2.8
(b) pH 4.5
(c) pH 7.5

I need to find out what kind of relationship Ka has to pH, does it have to do with pKa?

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1. The way you do these is to convert those Ka values to pKa = -log Ka.
Then the best acid/conjugate base is the acid with a pKa = +/- 1 of the pH you want for the buffer. For example,
pKa for acetic acid is 4.74 and that would be the best acid (conjugate base is acetate ion) to use to prepare a buffer system with pH = 4.5.

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