Hydrogen peroxide Reactions, Physical Properties an Uses| H2O2

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

H2O2 molecule shape bond length - laptop structure

Physical Properties of hydrogen peroxide

  • 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
  • Has weak acidic characteristics
  • Completely miscible with water, alcohol, and ether in all proportions. Hydrogen peroxide forms a hydrate with water as H2O2.H20.


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.



Acidic nature of hydrogen peroxide

Pure hydrogen peroxide is a weak acid dissociates as follow. It's Ka value is 1.55 * 10-12 mol dm-3 at 298K.

  • First dissociation forms hydronium ion and hydroperoxide ion.
  • Second dissociation forms again hydronium ion and peroxide ion.
hydrogen peroxide acidic reactions in the water

Storage of hydrogen peroxide

Hydrogen peroxide is stored in wax-lined glass or plastic vessels in the presence of stabilizers such as urea. Also it should be kept away from dust because dust can induces explosive decomposition.



Hydrogen Peroxide Preparing


Alkali metal peroxide and water reaction

Alkali metals peroxides ( 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 an 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

Enthalpy change for the reaction is -196.0 kJ

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-.

2KI + H2O2 + H2SO4 = I2 + 2H2O + K2SO4

2KI +I2O2 = KI3



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.

PbS + 4H2O2 = PbSO4 + 4H2O



Importance of PbS and H2O2 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. Then lead sulfate, a white precipitate is given.



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+.

2FeCl2+ + H2O2 + 3H2SO4 = Fe2(SO4)3 + 4HCl + 2H2O



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.

H2SO3 + H2O2 = H2SO4 + H2O

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



Hydrogen peroxide and hydrogen sulfide reaction

Hydrogen sulfide is oxidized to sulfur and hydrogen peroxide is reduced to water.

H2S + H2O2 = S + 2H2O



Hydrogen peroxide and NaOH reaction

NaOH reacts with hydrogen peroxide and produce sodium hydroperoxide which is an acidic salt. With excess NaOH, hydrogen peroxide forms sodium peroxide which is a normal salt.

NaOH + H2O2 = NaHO2 + H2O

2NaOH + H2O2 = Na2O2 + 2H2O



Oxidizing reactions in alkaline medium

Hydrogen peroxide can accept electrons in the alkaline medium and behave as an oxidizing agent.



Manganese sulfate and hydrogen peroxide reaction in alkaline medium

Manganese sulfate is oxidized to manganese dioxide while hydrogen peroxide is reduced to water. Manganese dioxide is a red-brown precipitate.

MnSO4 + NaOH + H2O2 = MnO2 + Na2SO4 + H2O



Metal nitrites, sulphites and arsenites are oxidized to nitrate, sulphates and arsenates respectively in alkaline medium.

NaNO2 + H2O2 = NaNO3 + H2O

Na2SO3 + H2O2 = Na2SO4 + H2O

Na3AsO3 + H2O2 = Na3AsO4 + H2O



Hydrogen peroxide as a reducing agent

Hydrogen peroxide can behave as a reducing agent in both acidic and basic mediums.


Potassium permanganate and hydrogen peroxide in acidic medium

Acidified potassium permanganate is reduced to colourless manganese sulfate and hydrogen peroxide is oxidized to oxygen gas. Acidified potassium permanganate solution is purple colour.

2KMnO4 + 5H2O2 + 6H2SO4 = 2MnSO4 + 5O2 + K2SO4 + 8H2O



Potassium dichromate and hydrogen peroxide reaction in acidic medium

Acidified orange colour potassium dichromate solution is oxidized to green colour chromium salt while hydrogen peroxide is oxidized to oxygen gas.

K2Cr2O7 + 3H2O2 + 4H2SO4 = Cr2(SO4)3 + 3O2 + K2SO4 + 7H2O



Manganese dioxide and hydrogen peroxide reaction

In acidified medium, brown-black colour manganese dioxide is reduced to manganese sulfate. Oxygen is given by the oxidation of hydrogen peroxide.

MnO2 + H2O2 + H2SO4 = MnSO4 + O2 + 2H2O



Ozone reduction

Ozone is reduced to dioxygen molecule.

O3 + H2O2 + H2SO4 = 2O2 + 2H2O



With hypochlorous acid

Hypochlorous acid is reduced to chloride ion in acidic medium.

HOCl + H2O2 + H2SO4 = H3O+ + O2 + Cl-



Potassium permanganate reduction in alkaline medium

Potassium permanganate is reduced to manganese dioxide while oxygen is oxidized to oxygen gas.

2KMnO4 + 3H2O2 = MnO2 + 3O2 + 2H2O + 2KOH



With ferric ion in alkaline medium

Ferric ions are reduced to ferrous ion by hydrogen peroxide which is oxidized to dioxygen molecule.

2FeCl3 + H2O2 + 2NaOH = 2FeCl2 + O2 + 2H2O + 2NaCl



Potassium ferricyanide reduction

When potassium ferrycyanide reacts with hydrogen peroxide in a alkaline medium, potassium ferrocyanide is given as the reduction product.

2K3[Fe(CN)6] + H2O2 + 2KOH = 2K4[Fe(CN)6] + O2 + 2H2O



Oxides of metals reduction to metals or metal oxide

Some metal oxides can be reduced to metal or higher oxidation state metal oxides can be reduced to lower oxidation state metal oxide.

  • Silver oxide is reduced to silver
  • Lead dioxide is reduced to lead oxide

Ag2O + H2O2 = 2Ag + O2 + H2O

PbO2 + H2O2 = PbO + O2 + H2O



Uses of hydrogen peroxide

  • As a bleaching agent for textiles, paper, pulp, leather, oils, fats and more
  • As a mild disinfectant
  • To produce inorganic compounds such as sodium perborates, sodium percarbonates which are important constituents of high quality detergents.
  • As pollution control agent. Oxidizing cyanides and restoration of aerobic conditions to sewage wastes.
  • As an antiseptic for washing wounds
  • To get back the white colour of lead paintings. White colour of lead carbonate will turn to black when occurs the contact with hydrogen sulfide due to formation of lead sulfide. Then lead sulfide reacts with hydrogen peroxide and forms lead sulfide, white colour compound.
  • In food industry - tartaric acid production
  • In pharmaceuticle industry - cephalosoporin


Summary of hydrogen peroxide reactions

hydrogen peroxide reactions and physical properties