Hydrogen peroxide Reactions and Physical Properties | H2O2

Hydrogen peroxide is a very famous chemical compound in the people. It is used as a disinfectant in cleaning injuries.

Physical Properties

  • When hydrogen peroxide exists as pure, viscous at liquid state, it is colourless.
  • When at solid state, hydrogen peroxide is a white crystal.
  • Also at higher temperature, H2O2 may be explosive.
  • When exposes to the sunlight, hydrogen peroxide decomposes to oxygen gas and water.
  • Boiling point: 1500C


Why boiling point of hydrogen peroxide is higher than water?

Boiling points of hydrogen peroxide and water are 1500C and 1000C respectively. We know both hydrogen peroxide and water are able to make hydrogen bonds.

Following factors will increase boiling points of compounds

  • Ability to make how many hydrogen bonds can be formed?
  • When molecular mass high, boiling point increases.

Molecular masses of H2O2 and H2O are 34 and 18 respectively. Also hydrogen peroxide molecules have the ability to make more hydrogen bond than water molecules. Due to both greater molecular mass and number of hydrogen bonds, boiling point of hydrogen peroxide is higher than water.



Hydrogen Peroxide Preparing

Alkali metal peroxide and water reaction

Alkali metals peroxide ( Na2O2, K2O2 ) will react with water and produce hydrogen peroxide and metal hydroxide.
Na2O2 + H2 → NaOH + H2O2
K2O2 + H2 → KOH + H2O2



Reactions of hydrogen peroxide

Hydrogen peroxide can react in different ways.

  • As a oxidizing agent
  • As a reducing agent


Decomposition of Hydrogen Peroxide

Hydrogen peroxide decomposes into water and oxygen gas (O2) when temperature increases or exposing to the sunlight. This reaction can be catalyzed by minute traces of transition metal ions. In the presence of potassium iodide, MnO2 aqueous NaOH will also catalyze the decomposition of H2O2. Also decomposition of H2O2 is an oxidizing-reducing reaction.

2H2O2 → 2H2O + O2

But decomposition will slow down when acids are present. ( H2SO4 ).

This reaction is a disproportionation process. Two half reactions (oxidation and reduction) are occurred.



As an oxidizing agent

Hydrogen peroxide is reduced to water and other compound is oxidized.



Potassium iodide and hydrogen peroxide reaction in acidic medium | KI + H2O2 = I2 + H2O

Potassium iodide is oxidized to iodine and hydrogen peroxide is reduced to water. Also in the presence of excess potassium iodide produced iodine combines with iodide ion give red - brown I3-.



With Lead sulfide | PbS + H2O2 = PbSO4 + H2O

Lead sulfide is a black precipitate and reacts with hydrogen peroxide and produce lead sulfate ( PbSO4 ) and water as products. PbSO4 is a white precipitate.


Importance of PbS and H2SO4 reaction

PbCO3 is a white inorganic compound. It is used as a pigment. But due to presence of H2S, PbCO3 is turned to black colour PbS. To take back the white colour, hydrogen peroxide is reacted with lead sulfide.



With ferrous ion in acidic medium | Fe2+ + H2O2 = Fe3+ + H2O

Ferrous ion ( iron(ii) ) is oxidized to ferric ion ( iron(iii) ) and H2O2 is reduced to water. Green colour of Fe2+ solution is changed to brown - yellow colour due to production of Fe3+.



Sulfurous acid and Hydrogen Peroxide Reaction | H2SO3 + H2O2 = H2SO4 + H2O

Sulfurous acid is oxidized to sulfuric acid. So oxidation number of sulfur is increased from +4 to +6. As other product, water is given.

Sulfurous acid is a weak acid and sulfuric acid is a strong acid.



Chromium +3 ion and Hydrogen Peroxide Reaction in Basic Medium | Cr3+ + H2O2 = CrO42- + H2O

  • Aqueous Cr3+ solution is green colour and oxidized to yellow colour CrO42-.
  • H2O2 is reduced to water.


Summary of hydrogen peroxide reactions

hydrogen peroxide reactions and physical properties