H2O2 has open-book (non-planar) structure. O is in -1 oxidation state. Dihedral angle: 111.5 degrees (gas), 90.2 degrees (solid). As oxidiser: H2O2 + 2KI → I2 + 2KOH; H2O2 + 2$Fe^{2+}$ + 2$H^+$ → 2$Fe^{3+}$ + 2H2O; PbS (black) + 4H2O2 → PbSO4 (white) + 4H2O (restores old paintings). As reducer: 2$MnO4^-$ + 5H2O2 + 6$H^+$ → 2$Mn^{2+}$ + 5O2 + 8H2O; Cl2 + H2O2 → 2HCl + O2. Volume strength: "x volume" means 1 mL of H2O2 solution gives x mL of O2 at STP. Formula: Volume strength = 11.2 x Molarity = 5.6 x Normality. Stored in dark wax-coated bottles (light and rough surfaces catalyse decomposition). MnO2, Pt, and catalase enzyme decompose H2O2.