Physical properties of Hydrogen Peroxide
(i) Hydrogen peroxide is a pale blue syrup liquid.
(ii) Hydrogen peroxide boils and decomposes at 150C and freezes at about -0.9C
(iii) Hydrogen peroxide dissolves in water to give a very weak acidic solution.
Chemical Properties of Hydrogen Peroxide
(i) Decomposition: Hydrogen peroxide decomposes to form water and oxygen when exposed to air. This decomposition is exothermic and is accelerated by heating, addition of alkalis and the introduction of finely divided metals such as platinum, gold and manganese(IV) oxide which acts as a catalyst.
2H2O2(l) → 2H2O(l) + O2(g)
Mineral acids and propane-1,2,3-triol inhibits the decomposition of hydrogen peroxide. These compounds are often added to commercial hydrogen peroxide to minimize its decomposition.
(ii) Hydrogen Peroxide as an oxidizing agent: Hydrogen peroxide is a strong oxidizing agent as it can readily donate oxygen or accept electrons. In this process, it is reduced to water. Its oxidative property can be seen in its reaction with potassium iodide solution that has been acidified with tetraoxosulphate(VI) acid, where it liberates iodine. The tetraoxosulphate(VI) acid first reacts with the iodide to form iodic acid, HI, which is subsequently oxidized by hydrogen peroxide to liberate iodine. The oxidation process carried out by hydrogen peroxide is done by its acceptance of electrons from the iodide ion, and itself being reduced to water.
2KI(aq) + H2O(aq) +H2SO4(aq) →K2SO4(aq) + 2H2O(l) +I2(aq)
(iii) Hydrogen Peroxide as a reducing agent: Hydrogen peroxide can also behave like a reducing agent when it reacts with more powerful oxidizing agents by either donating electrons or accepting oxygen. The reduction process leads to hydrogen peroxide itself being converted to gaseous oxygen. For instance, hydrogen peroxide reduces acidified potassium tetraoxomanganate(VII) solution making it colorless because the purple tetraoxomanganate(VII) ion is changed in to the pale pink manganese(II) ion.
2KMnO4(aq) + 3H2SO4(aq) + 5H2O2(aq) → K2SO4(aq) + 2MnSO4(aq) 8H2O(l) + 5O2(g)
Hydrogen peroxide can equally reduce chlorine to hydrochloric acid and silver oxide to the metal.
Cl2(g) + H2O2(aq) → 2HCl(aq) + O2
Ag2O(s) + H2O2(aq) → 2Ag(s) + H2O(l) O2