Hydrogen Peroxide

Hydrogen Peroxide - Structure, Uses and Properties

Hydrogen peroxide is a highly unstable chemical compound. Two molecules of hydrogen combine with two molecules of oxygen to form hydrogen peroxide. Hence, its chemical formula is H2O2. Hydrogen peroxide is a pale blue, clear liquid, slightly more viscous than water in its pure form. It is the simplest peroxide (since it is a compound with an oxygen-oxygen single bond). Hydrogen peroxide has basic uses as an oxidizer, bleaching agent and antiseptic. Concentrated hydrogen peroxide, also known as "high-test peroxide", is a reactive oxygen species and has been used as a propellant in rocket propulsions. As this compound is unstable, it slowly decomposes in the presence of light. Hydrogen peroxide is generally stored with a stabilizer in a weakly acidic solution since it is unstable. It can be found in biological systems including the human body. Peroxidases are the enzymes that use or decompose hydrogen peroxide.

HISTORY OF DISCOVERY


In 1799, Alexander von Humboldt synthesized barium peroxide, one of the first synthetic peroxides, as a by-product of his attempts to decompose air. After nineteen years, Louis Jacques Thénard stated that this compound could be used for the preparation of a previously unknown compound. He described it as eauoxygénée (French: oxygenated water) – which came to be known as hydrogen peroxide. An advanced version of Thénard's method used hydrochloric acid, followed by addition of sulfuric acid to precipitate the barium sulfate by-product. This method was followed from the end of the 19th century until the middle of the 20th century. In 1811, Thénard and Joseph Louis Gay-Lussac synthesized sodium peroxide. Pure hydrogen peroxide was initially believed to be unstable since early experiments to separate it from the water, which is present during synthesis,- all failed. This instability was present owing to traces of impurities (transition-metal salts). These impurities catalyze the decomposition of the hydrogen peroxide. Richard Wolfenstein first obtained pure hydrogen peroxide in 1894. He produced it by vacuum distillation.

STRUCTURE OF HYDROGEN PEROXIDE


The structure of hydrogen peroxide is non-planar which means that it has a three-dimensional quality. The structure for this compound is also popularly known as open book structure. The following diagram will explain the statement.



The diagram shows that there are two planes in the structure and each plane has one O-H pair, the angle between both the planes is 90.2°, The length of O-O bond is 145.8 pm and the O-H bond length is 98.8 pm(which equals to 9.88 × 10-13 m). Two pairs of unbound electrons will be present in both oxygen atoms. This proves the valence shell electron repulsion theory. The hydrogen atoms will always repel the un-bonded electrons of oxygen. Hence, the bent molecular shape is formed.
Various methods are involved in the preparation of hydrogen peroxide:

  • • When acidification of barium peroxide takes place and the excess water is removed by the process of evaporation under reduced pressure, we obtain hydrogen peroxide. The following reaction vouches for the fact:

  • • P/ρ+gz+v2/2=k

  • • P/ρ+gz+v2/2=k

  • • BaO2.8H2O(s)+H2SO4(aq)→BaSO4(s)+H2O2(aq)+8H2O(l)

  • • When acidified sulfate solution is electrolyzed at high current density, peroxodisulphate can be obtained. Peroxodisulphate then needs to be hydrolyzed to get hydrogen peroxide.

  • • 2HSO−4(aq) Electrolysis−→−−−−−−− HO3SOOSO3H(aq) Hydrolysis−→−−−−−−− 2HSO−4(aq)+2H+(aq)+H2O2(aq)


  • PROPERTIES OF HYDROGEN PEROXIDE


    The properties of hydrogen peroxide are as follows:

  • • Hydrogen peroxide is almost colorless (very pale blue) in a pure state.

  • • Its boiling point has been extrapolated at a temperature as high as 150.2 C which is almost 50 C higher than the boiling point of water.

  • • The melting point of hydrogen peroxide is -0.43 C.

  • • It forms a homogenous mixture in water in all proportion and form hydrates.

  • • 34.0147 g/mol is the molar mass of hydrogen peroxide.

  • • It has a slightly sharp odor.

  • • Its density is 1.11g/cc in aqueous solution and 1.450 g/cc in its pure form.

  • • Hydrogen peroxide is soluble in ether, alcohol but insoluble in petroleum ether.

  • Chemical properties of hydrogen peroxide are as follows:

    Hydrogen peroxide acts both as an oxidizing as well as the reducing agent in acidic and also in basic medium. The following reactions depict the picture:

  • • Oxidizing nature in an acidic medium

  • • PbS(s)+4H2O2(aq)→PbSO4(s)+4H2O(l)

  • • The reducing nature in an acidic medium

  • • HOCl+H2O2→H3O++Cl−+O2

  • • Oxidizing nature in a basic medium

  • • Mn2++H2O2→Mn4++2OH−

  • • Reducing nature in a basic medium

  • • I2+H2O2+OH−→2I−+2H2O+O2


  • STORAGE OF HYDROGEN PEROXIDE


    When exposed to sunlight, hydrogen peroxide decomposes. This decomposition process is catalyzed by traces of alkali metals. Therefore, hydrogen peroxide can be stored in wax-lined glass or plastic containers and are kept in the dark. It must also be kept away from dust particles as dust can induce explosive decomposition of this compound.


    USES OF HYDROGEN PEROXIDE


    Hydrogen peroxide has a number of uses. Some of them are listed below:

  • • Bleaching: Hydrogen peroxide is used as a bleaching agent in the textile and paper industry. Data suggests that almost about 60% of the world's production of hydrogen peroxide is used for pulp- and paper-bleaching.

  • • Hydrogen peroxide can be used as hair bleach in our daily life and also as a mild disinfectant.

  • • Detergents: One of the major industrial applications of this compound is the manufacture of sodium percarbonate and sodium perborate, which are used as mild bleaches in laundry detergents. Sodium percarbonate is an active ingredient in products as OxiClean and Tide laundry detergent. It releases hydrogen peroxide and sodium carbonate when dissolved in water.

  • • Production of organic compounds: Hydrogen peroxide is used in the production of several organic peroxides with dibenzoyl peroxide being a high volume example. It is used in polymerizations, as a flour bleaching agent and also as a treatment for acne.

  • • Hydrogen peroxide has also been used in certain waste-water treatment processes to remove organic impurities.

  • • Hydrogen peroxide is used to sterilize various surfaces including surgical tools and it may be deployed as a vapor (VHP) for room sterilization.


  • • Hydrogen peroxide is an environmentally secure substitute to chlorine-based bleaches, as it degrades to form water and oxygen and it is normally accepted as safe as an antimicrobial agent by the U.S. Food and Drug Administration (FDA).


  • • Since time immemorial, hydrogen peroxide had been used for disinfecting wounds, partly because of its low cost and prompt availability compared to other antiseptics. However, in recent times, it is thought to inhibit healing and to induce scarring because it destroys newly formed skin cells.

  • • Dermal exposure to dilute solutions of hydrogen peroxide can cause bleaching or whitening of the skin

  • • Hydrogen peroxide has wide application in certain cosmetic production as well.

  • • It is present in most whitening toothpaste. One can mix this compound with baking soda and salt to make a home-made toothpaste.

  • • This compound is widely used in the production of alternative medicine. The use of hydrogen peroxide can cure various conditions, including emphysema, influenza, AIDS, and cancer although there is no proper evidence of effectiveness and in some cases, it may even be life-threatening.


  • • Hydrogen peroxide can be used as a propellant in the rocket industry. Rocket-belt hydrogen peroxide propulsion systems are used in a jet back.


  • • Other uses of hydrogen peroxide include:

  • • Glow sticks

  • • Horticulture: Some horticulturalists and users of hydroponics suggest the use of a weak hydrogen peroxide solution in watering solutions.

  • • Fish aeration:

  • Hence hydrogen peroxide is one of the most important compounds.