
\[\underset{\begin{smallmatrix}
|\,\,\,\,\,\,\,\,\,\,\, \\
\,\,\,\,\,\,\,\,\,\,\,\,C{{H}_{2}}C{{H}_{2}}COOH
\end{smallmatrix}}{\mathop{{{H}_{3}}\overset{+}{\mathop{N}}\,-CH-CO{{O}^{-}}}}\,\xrightarrow[\text{ionization}]{\text{Second}}\] \[\underset{\begin{smallmatrix}
|\,\,\,\,\,\,\,\,\,\, \\
\,\,\,\,\,\,\,\,\,\,\,\,C{{H}_{2}}C{{H}_{2}}CO{{O}^{-}}
\end{smallmatrix}}{\mathop{{{H}_{3}}\overset{+}{\mathop{N}}\,-CH-CO{{O}^{-}}}}\,\]
$$\eqalign{
& {\text{So,}}\,\,pI = \frac{{p{K_{{a_1}}} + p{K_{{a_3}}}}}{2} \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \frac{{2.2 + 4.3}}{2} \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 3.25 \cr} $$