Consider the thermal disproportionation of elemental white phosphorus in a basic medium: . When this — Redox Reactions and Volumetric Analysis Chemistry Question
Question
Consider the thermal disproportionation of elemental white phosphorus in a basic medium: $P_4 + OH^- + H_2O \to PH_3 + H_2PO_2^-$ . When this skeletal equation is perfectly balanced utilizing the smallest whole-number coefficients, what is the required stoichiometric coefficient of water ( $H_2O$ )?
💡 Solution & Explanation
Utilizing the ion-electron method: Oxidation half is $P_4 + 8OH^- \to 4H_2PO_2^- + 4e^-$ (multiply by 3). Reduction half is $P_4 + 12H_2O + 12e^- \to 4PH_3 + 12OH^-$ . Adding them algebraically gives: $4P_4 + 12H_2O + 12OH^- \to 4PH_3 + 12H_2PO_2^-$ . Dividing the entire resulting equation by its common denominator of 4 yields the simplest whole-number balanced equation: $P_4 + 3H_2O + 3OH^- \to PH_3 + 3H_2PO_2^-$ . The final coefficient for water is 3.