The following two reactions describe the chemistry of S(IV) in an aquatic system.
Under ideal conditions, the equilibrium constants for reactions (i) and (ii) are \(1.3\times10^{-2}\ M\) (\(K_{S1}\)) and \(6.6\times10^{-8}\ M\) (\(K_{S2}\)), respectively.
If the pH of the system is 4.0 and the equilibrium concentration of \(SO_{2(aq)}\) is 1.0 M, the equilibrium concentration of \(SO_3^{2-}\) is ______ mM (rounded off to one decimal place).
\[SO_{2(aq)} \rightleftharpoons H^+ + HSO_3^- \quad (i)\]
\[HSO_3^- \rightleftharpoons H^+ + SO_3^{2-} \quad (ii)\]