For  a concentrated solution of a weak electrolyte (K_eq = equilibrium constant ) A₂B₃ of concentration ‘c’, the degree of dissociation ‘α’ is 

           ${\mathrm{A}}_2{\mathrm{B}}_3\rightleftharpoons 2{\mathrm{A}}^{3+}+3{\mathrm{B}}^{2-}$

Initial    C

final $\mathrm{C}-\mathrm{C}\alpha 2\mathrm{C}\alpha \left(3\mathrm{C}\alpha \right)$

From law of mass action

$\begin{array}{l}{\mathrm{K}}_{\mathrm{eq}}=\frac{(2\mathrm{C}\alpha {)}^2\times (3\mathrm{C}\alpha {)}^3}{(\mathrm{C}-\mathrm{C}\alpha )}\\ \alpha <<1\Rightarrow 1-\alpha \simeq 1\\ {\mathrm{K}}_{\mathrm{eq}}=\frac{2^2\times 3^3\times {\mathrm{C}}^5\times {\alpha }^5}{(1-\alpha )\times \mathrm{C}}\Rightarrow {\mathrm{K}}_{\mathrm{eq}}=108{\mathrm{C}}^4\times {\alpha }^5\\ \Rightarrow \alpha ={\left(\frac{{\mathrm{K}}_{\mathrm{eq}}}{108{\mathrm{C}}^4}\right)}^{\frac{1}{5}}\end{array}$