Hydrogen Peroxide: Structure, Preparation & Uses

Hydrogen peroxide refers to a chemical element that is a pale blue, syrupy liquid that breaks down quickly into oxygen and water. Composed of hydrogen and oxygen, the chemical formula for compound is H₂O₂.

• Hydrogen peroxide is a form of reactive oxygen species that is more viscous than water.
• It is a thermodynamically most unstable liquid that is decomposed explosively when heated.
• The compound was discovered by Louis Jacques Thénard in 1818.
• We are using this compound in our day-to-day lives without even realising it.
• You can use this compound as an oxidizer in rocketry, a bleaching agent, and an antiseptic.
• Hydrogen peroxide can be used as a monopropellant and is found in human biological systems.

Key Terms: Hydrogen peroxide, H₂O₂, Hydrogen, Oxygen, Covalent bond, Peroxide, Structure of Hydrogen Peroxide, Bleaching Agent, Atom

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Structure of Hydrogen Peroxide

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The structure of H₂O₂ is in the form H—O—O—H where each dash represents a single covalent link. In other words, each bond has a pair of mutual electrons, one from each of the atoms at the bond’s ends. The H—O bonds are polar, but not the O—O bonds.

• Each oxygen atom here is combined to a hydrogen atom with the use of a single bond.
• Due to repulsion between lone pairs of electrons over oxygen atoms, the two bonds can not reside in the same plane. 
• Hydrogen peroxide is a non-planar substance containing the peroxide ions (O₂-).
• The peroxide ion is made up of a single bond formed by two oxygen atoms.

Hydrogen Peroxide Structure

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Properties of Hydrogen Peroxide

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The physical and chemical properties of hydrogen peroxide are as follows:

Physical Properties of Hydrogen Peroxide

The physical properties of H₂O₂ are as follows:

• In its pure state, hydrogen peroxide is an almost transparent colourless liquid with a nitric acid-like odour.
• The consistency of the compound is much better than that of water, with a density of about 40% that of water.
• The boiling point of hydrogen peroxide form is roughly 150.2°C. 
• On the other hand, it suffers a thermal breakdown and has an explosive reaction at such a temperature. 
• This is why most hydrogen peroxide is kept in aqueous form. 
• It is usually stored in dark-coloured containers to prevent it from interacting with light.
• The melting point of H₂O₂ is −0.43°C (31.23 °F; 272.72 K).

The physical properties of hydrogen peroxide are tabulated below:

Chemical Properties of Hydrogen Peroxide

The chemical properties of H₂O₂ are as follows:

• Hydrogen peroxide is dissolvable in water, which means that when it is mixed with water, it produces a homogenous solution.
• The oxidising agent H₂O₂ is quite powerful because it gives up one oxygen atom and creates water.

PbS + 4H₂O₂ → PbSO₄ + 4H₂O (in acidic medium)

2Fe + H₂O₂ → 2Fe + 2OH (in basic medium)

• The compound decomposes on heating in the presence of metals, such as Cu, Ag, Ca, Fe, MnO₂, carbon, alkali oxides and light.

  H₂O₂ + H₂O₂ → 2 H₂O + O₂

• Hydrogen peroxide acts as a weak acid, neutralising carbonates and alkalis, forming two salts, hydroperoxides and peroxides.

H₂O₂ ⇔ H⁺ + HO₂^–

H₂O₂ ⇔ H⁺ + O₂^²-

• It can also operate as a reducing agent in the presence of a strong oxidising agent and release oxygen every time.

H₂O₂ → 2H⁺ + 2e- + O₂ (Acidic medium)

H₂O₂ + 2OH^– → 3H₂O + 2e- +O₂ (Basic medium)

• The compound is used as a bleaching agent, which converts colouring matter into colourless matter with nascent oxygen.

H₂ O₂ → 2H ₂ O + O

• The aqueous solution of hydrogen peroxide is extremely volatile, and it is gradually disproportionate to give oxygen and water.

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Preparation of Hydrogen Peroxide

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Various techniques involved in the preparation of hydrogen peroxide are as follows:

Laboratory Method

This process creates hydrogen peroxide in the lab using barium peroxide. Anhydrous BaO₂ will act as a barrier layer and will not react with the sulphuric acid. The H₂O₂ that is formed is a 5% concentration solution.

BaO₂.8H₂O + H₂SO₄ → BaSO₄ + H₂O₂ + 8H₂O

Merck’s Method

We’ll use a dilute solution of sulphuric acid to dissolve sodium peroxide. Since H₂O₂ is highly flammable at high temperatures, we employ cold sulphuric acid.

• When these two react, we receive crystals of sodium sulphide and a 30% solution of hydrogen peroxide.
• To obtain pure hydrogen peroxide, one should vacuum distill the aforementioned solution.

Na₂O₂ + H₂SO₄ → Na₂SO₄ + H₂O₂ (30%)

Bubbling CO₂ through a paste of BaO₂

We can also prepare hydrogen peroxide by bubbling CO₂ through a mixture of BaO₂ .

BaO₂ +H₂ O+ CO₂ → BaCO₃ + H₂ O₂

Electrolysis of 50% H₂ SO₄ (Manufacture of H ₂ 0 ₂ )

Hydrogen peroxide can be prepared by electrolusing the 50% solution of sulphuric acid. It will use Pt as the anode and graphite as the cathode. 

• Peroxodisulphuric acid is distilled with water under low pressure.
• The low boiling of the compound distils with the water, leaving behind the H ₂ SO ₄ solution.
• The reaction of preparation are as follows:

2H₂ SO₄ → 2H ⁺ + 2HSO ₄ ^–

• At the cathode:

2H ⁺ + 2e→H2

• At the anode:

2HSO₄ ^– → H₂ S₂ O₈ + 2e

Auto Oxidation of 2-Ethyl Anthraquinone

2-Ethyl Anthraquinone contains 10% solution in benzene and cyclohexane. In this process, hydrogen peroxide reacts with 2-ethyl anthraquinone in the presence of a Pd catalyst to form 2-ethyl anthraquinone.

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Hydrogen Peroxide Storage

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Hydrogen peroxide breaks down when exposed to sunlight. Alkali metal traces act as catalysts for this dissolution process. Hydrogen peroxide can therefore be preserved in the dark in wax-lined glass or plastic containers. It should also be stored away from dust particles, as this substance can decompose explosively if exposed to them.

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H₂O₂ Uses

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Given below are the uses of hydrogen peroxide:

Disinfectant

Hydrogen peroxide helps fight against germs, as well as most viruses and bacteria. A sanitizer with a concentration of 3% is widely available in the marketplace. 

• It is important to handle hydrogen peroxide with caution as it can damage certain surfaces.
• The compound should be mixed with water and washed down the same way bleach is washed down.
• Hydrogen peroxide should be used carefully as it can stain garments and porous countertops.

Bleaching Agent

H₂O₂ is also used to bleach fabrics. Due to its oxidising characteristics, it can directly interact with double bonds in large organic molecules, creating organic peroxides. 

• In this method, hydrogen peroxide is being used to bleach wood pulp for white paper and hair melanin.
• It is the most widely utilised chemical for high-yield pulp and paper bleaching when high degrees of brightness are required.

Uses for Plants

Hydrogen peroxide can be used to cultivate a wide variety of plants in hydroponic gardens, raised beds, and greenhouses. By releasing oxygen, it acts as an oxygen substitute for plants. 

• It is very advantageous to the health and development of plants. 
• Hydrogen peroxide can also help treat soil fungal problems.
• The compound aids the growth of oxygen levels in water. 
• It will also aid in the eradication of any mould or fungus-causing germs. 
• This method will kill fungus gnat eggs and larvae. 
• The solution will also help supply oxygen to the soil of your indoor plants, as well as eliminate any other bacterial or fungal problems.

Dentistry

Hydrogen peroxide is utilised safely and effectively in dentistry nowadays. Though tooth whitening is the most widely used application, the compound has been demonstrated to be effective in treating gingivitis and periodontitis.

• Gargling hydrogen peroxide can aid in sore throat, mouth disinfection, and tooth whitening.
• Due to its antimicrobial qualities, the compound can help treat gum disease. 
• A biofilm is a sticky bacterial film that forms on the teeth when plaque builds. 
• The production of oxygen by hydrogen peroxide aids in the killing of microorganisms.
• Using a large dose of teeth whitening gel can also affect the soft tissues in the mouth.
• The gums will turn white and blister as a painful reaction to this stiff gel. 
• These wounds, fortunately, are only transient and heal quickly.

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Things to Remember

• Hydrogen peroxide refers to a chemical element that includes hydrogen and oxygen. 
• Its pure state is an almost transparent colourless liquid with a nitric acid-like odour. 
• It has various uses, such as being a mild antiseptic that can be used on small cuts, scrapes, and burns to prevent infection.
• Overdose or overuse of hydrogen peroxide can also have negative effects on health. 
• It irritates the eyes when it comes into touch with them.

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