Hydrogen peroxide (H₂O₂) Reactions and Chemical Properties

Hydrogen peroxide is one of the common chemical used in laboratory scale for lot of purposes. Because oxidation number of Oxygen atom in Hydrogen peroxide molecule is at -1, Hydrogen peroxide can behave as an oxidizing agent and reducing agent. Therefore H₂O₂ shows various types of reactions and we will study in detail in this tutorial.

Content

• Lewis structure and oxidation numbers of hydrogen peroxide
• Acidic nature of hydrogen peroxide
• Storage of hydrogen peroxide due to decomposition possibility
• Reactions of hydrogen peroxide
  • Decomposition of Hydrogen Peroxide
  • Reaction where hydrogen peroxide behave as an oxidizing agent in acidic or neutral solutions
  • Reaction where hydrogen peroxide behave as an oxidizing agent in alkaline medium
  • Reactions of Hydrogen peroxide as a reducing agent
• Summary of hydrogen peroxide reactions

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Lewis structure and oxidation numbers of hydrogen peroxide

Identifying the lewis structure of H₂O₂ molecule is a mandatory to understand the reactions. According to the following structure, oxidation number of each oxygen atom is at -1 while each hydrogen atom's oxidation is +1. Because oxidation number of oxygen is -1 in Hydrogen peroxide, that oxugen atoms can be undergone in both oxidation and reduction reactions. Usually, when Hydrogen peroxide is reduced, water is given and when Hydrogen peroxide is oxidized, oxygen gas is given as products.

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.

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.

Reactions of hydrogen peroxide

Hydrogen peroxide can react in different ways because oxygen atom in H₂O₂ molecule can be reduced or oxidized.

• Decomposition of Hydrogen Peroxide
• As an oxidizing agent - Hydrogen peroxide is reduced to water
• As a reducing agent - Hydrogen peroxide is oxidized to oxygen gas

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 in the solution. ( H₂SO₄ ).
• This reaction is a disproportionation process. Two half reactions (oxidation and reduction) are occurred.

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Reaction where hydrogen peroxide behave as an oxidizing agent in acidic or neutral solutions

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.

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⁺.

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 = CrO₄^2- + H₂O

• Aqueous Cr³⁺ solution is green colour and oxidized to yellow colour CrO₄^2-.
• H₂O₂ is reduced to water.

Hydrogen peroxide and hydrogen sulfide reaction

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

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.

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Reaction where hydrogen peroxide behave as an oxidizing agent 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.

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

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Reactions of 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.

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.

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.

Ozone reduction

Ozone is reduced to dioxygen molecule.

With hypochlorous acid

Hypochlorous acid is reduced to chloride ion in acidic medium.

Potassium permanganate reduction in alkaline medium

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

With ferric ion in alkaline medium

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

Potassium ferricyanide reduction

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

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

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Summary of hydrogen peroxide reactions

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Have Questions?

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what should a hydrogen peroxide reaction should be about?

HYdrogen peroxide can behave as an oxidizing agent or reducing agent. So, you have to remember how different compounds react with hydrogen peroxide.

hydrogen peroxide decomposes to water and oxygen. The decomposition reaction rate can be catalyzed by inorganic compounds or enzymes?

Decomposition of hydrogen peroxide will increase by inorganic compounds such as aqueous KI, NaOH, solid MnO₂.

manganese dioxide hydrogen peroxide reaction

If manganese dioxide is added to aqueous hydrogen peroxide, it accelerates the decomposition of hydrogen peroxide to water and oxygen gas.

If acidic manganese dioxide is used, hydrogen peroxide is oxidized to oxygen gas while manganese dioxide will be reduced to manganese +2 ion.

what reacts with hydrogen peroxide?

Hydrogen peroxide can behave as an oxidizing agent and reducing agent. So, hydrogen peroxide can react with many compounds.

• Hydrogen peroxide is oxidized to oxygen by strong oxidizing agents such as acidic KMnO₄ or K₂CrO₄ or KCr₂O₇.
• Silver oxide is reduced to silver by hydrogen peroxide.
• Fe²⁺ ions are oxidized to Fe³⁺ ions.

metal salts reaction with hydrogen peroxide

Ferric chloride is reduced to ferrous cations by hydrogen peroxide.

hydrogen peroxide reaction with ethanol

There are different references for this reaction ad we will summarize them.

According to the The oxidation of ethanol by hydrogen peroxide. Part I. Catalysis by ferric ion research, ethanol is oxidized to acetaldehyde in the presence of Fe³⁺ catalyst. They have used boiling ethanol for this rection.

Acidified hydrogen peroxide and ethanol reaction be an explosive one. Concentration of hydrogen peroxide should be high. But higher concentrations of H₂O₂ are dangerous.

Refer this tutorial: Can ethanol be oxidized by hydrogen peroxide?

Which are the compounds, which can be oxidized and reduced by H2O2 in acidic and basic medium respectively?

In acidic medium, permanganate ion is reduced to manganese +2 ion by H₂O₂.

In the basic medium, manganese +2 ion are oxidized to manganese dioxide (MnO₂) by H₂O₂.

hydrogen peroxide temperature range

For which thing, you asked that temperature range?

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