In the auto-redox (disproportionation) reaction , what is the equivalent weight ( ) of the reactant — Redox Reactions and Volumetric Analysis Chemistry Question

💡 Solution & Explanation

The oxidation state of P in $H_3PO_2$ is $+1$ . It reduces to $PH_3$ (O.S. = $-3$ ), representing a change of $4$ electrons ( $n_1 = 4$ ). It simultaneously oxidizes to $H_3PO_3$ (O.S. = $+3$ ), representing a change of $2$ electrons ( $n_2 = 2$ ). For a disproportionation reaction, the net equivalent weight is the sum of the equivalent weights of the two distinct half-reactions: $E = M/n_1 + M/n_2 = M/4 + M/2 = 3M/4$ .