Glutamic acid H2N−CH(CH2CH2COOH)−COOHN has pKa1(α−C

Discussion Forum : Surface Chemistry

Question -

Glutamic acid $H_{2} N - C H (C H_{2} C H_{2} C O O H) - C O O H N$ has $p K_{a 1} (α - C O O H) = 2.2, p K a 2 (R g r o u p C O O H) = 4.3$ . The isoelectric point of glutamic acid is

Options:

A . 5.9

B . 7.0

C . 10.2

D . 3.2

Answer: Option D
:
D

$H_{3} + N - C H | C H_{2} C H_{2} C O O H C a t i o n i c f o r m - C O O H O n n e u t r a l i s a t i o n ⟶ 1 s t i o n i z a t i o n H_{3} + N - C H | C H_{2} C H_{2} C O O H - C O O^{-} ⟶ 2 n d i o n i z a t i o n H_{3} + N - C H | C H_{2} C H_{2} C O O^{-} - C O O^{-}$
$I s o e l e c t r i c p o i n (p I) = \frac{p K_{a_{1}} + p K_{a_{3}}}{2}$
$\frac{2.2 + 4.3}{2} = 3.25$

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