Question

Glutamic acid [side chain R = (CH2)2CO2H] has pKa values of 2.19, 4.25 and 9.67. What would be the predominant species in solution at pH 8?

a) Carboxyl groups in neutral form.
b) Carboxyl groups in deprotonated form, amino group in deprotonated form.
c) Carboxyl groups in protonated form, amino group in deprotonated form.
d) Carboxyl groups in deprotonated form, amino group in protonated form.

Answer 1

The pH of 8 is closer to the pKa value of the carboxyl group's dissociation (pKa = 4.25) than to the amino group's dissociation (pKa = 9.67). Therefore, the carboxyl groups are still partially protonated and in the neutral form, while the amino group is in its deprotonated form.

The answer is (a) carboxyl groups in neutral form.