Question

The $pH$($pH$ at the isoelectric point) of the given amino acid is :

• A. $3.22$
• B. $6.96$
• C. $5.93$
• D. $8.05$

Answer 1

Answer: (C)

$5.93$

$\underset{pKa=4.25}{\underset{\uparrow }{HO}}-\stackrel{O}{\stackrel{||}{C}}-C{H}_2-C{H}_2-\underset{N{H}_3^{\oplus }}{\underset{|}{CH}}-\stackrel{O}{\stackrel{||}{C}}-\underset{pKa=2.190}{\underset{\uparrow }{OH}}$

$pKa=9.67$

$pH=\frac{(P_{k{a}^{{}_1}}{)}_{lowest}+(P_{k{a}^{{}_2}}{)}_{highest}}{2}$

$=\frac{2.19+9.67}{2}$

$pH=5.93$

The isoelectric point of amino acid is $5.93$.

Hence, the correct option is $C$.