Niacin, one of the B vitamins, is a monoprotic acid. A 0.020 M solution of niacin has a pH of 3.26. What is the acid dissociation constant, Ka, for the ionizable proton?
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Niacin is nicotinic acid and it is a monocarboxylic acid attached to heterocyclic pyridine nucleus.
pH = log[1/H+] = 3.26 ;
[H+] = 5.4954 X 10^-4 mole/L.
Niacin -COOH <=> Niacin-COO- + H+ ;
Ka = [H+]^2 / 0.02 = (5.4954 X 10^-4)^2 /0.02 = 1.5099 X 10^-5.
pH = log[1/H+] = 3.26 ;
[H+] = 5.4954 X 10^-4 mole/L.
Niacin -COOH <=> Niacin-COO- + H+ ;
Ka = [H+]^2 / 0.02 = (5.4954 X 10^-4)^2 /0.02 = 1.5099 X 10^-5.