Question

In aqueous solution $\alpha$-amino acid has the following equilibria.

Find the iso-electric point of the $\alpha$-amino acid given.

Answer 1

$pK _{ a _{1}}=-\log 5-\log 10^{-3} \approx 2.3$
$pK _{ b }=4.3$
$\Rightarrow pK _{ a _{2}}=9.7$
$\therefore p ^{1}=\frac{ pK _{ a _{1}}+ pK _{ a _{2}}}{2}$
$=\frac{2.3+9.7}{2}=6$