Propose buffer components to hold a pH = 4.0. Let the acid have a concentration of...

Question

Question

Propose buffer components to hold a pH = 4.0. Let the acid have a concentration of 0.21 M.

Identity Concentration

Acid ? 0.21 M

Base ? ?

Answer 1

Answer #1

as a rule of thumb if you want pH around 4 then select that acid whose pka lies such that pH = pka -1 to pKa +1

hence pKa should be between 3 - 5 hence acetic acid would be the ideal choice

applying Henderson equation

pH = pKa + log [base] / [acid]

pKa = -log Ka = -log (1.8*10^-5) = 4.74

and [acid] = 0.21

4 = 4.74 + log [base] / [0.21]

on solving

[base] = 0.038

Answer 2

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