Have you ever thought, what happens when we oxygenate a water molecule or when we add an extra oxygen atom to a water molecule? Water is then no more the life-saving liquid; instead, it becomes ‘oxygenated water’ aka ‘Hydrogen Peroxide‘, having properties way different than that of water. It is found in most medicine cabinets in the developed world.

Hydrogen peroxide – a green (environmental friendly) oxidant has wide application ranging from its industrial use in manufacturing different chemicals to its medical use as an antiseptic. In this article, we will discuss in detail about Hydrogen Peroxide, its structure, properties, preparation, etc. Read on to explore this chemical.

Discovery of Hydrogen Peroxide 

Hydrogen peroxide, first recognized as a chemical compound in \(1818\) by French chemist J.L Thenard, is the simplest member of the class of peroxides. Its molecular formula is \({{\rm{H}}_2}{{\rm{O}}_2}.\) In the environment, hydrogen peroxide can be discovered in very low concentrations. Gaseous hydrogen peroxide is produced by photochemical reactions in the atmosphere surrounding the earth. It acts as a bleaching agent and is also utilized as a disinfectant. It is acidic, and \({\rm{pH}}\) is in the range of \(6-7\) at \(298\;{\rm{K}}{\rm{.}}\)

Structure of Hydrogen Peroxide 

1. Peroxide is a chemical compound that contains the peroxide ion \(\left( {{\rm{O}}_{\rm{2}}^{{\rm{2 – }}}} \right){\rm{.}}\) The peroxide ion consists of a single bond between two oxygen atoms:\({{\rm{(O – O)}}^{{\rm{2 – }}}}{\rm{.}}\) It is a strong oxidizer. 
2. Hydrogen peroxide is a non-planar molecule, two oxygen atoms bonded together through a single covalent bond called the peroxide bond.
3. It has an open book structure. Each oxygen atom is further attached to a hydrogen atom through a single bond. The two bonds do not lie in the same plane because of the repulsion between lone pairs of electrons over oxygen atoms. The dihedral (interplanar) angle between the two planes is \({111.5^{\rm{o}}}\) if hydrogen peroxide is in a gaseous state, whereas, in its crystalline state, this angle reduces to \({90.2^{\rm{o}}}.\) This happens due to intramolecular hydrogen bonding. 

Study Preparation and Structure of Hydrogen Peroxide

The bond parameters of hydrogen bonding in the gaseous and crystalline phases are shown in the figures below:

Uses of Hydrogen Peroxide

Hydrogen peroxide is a versatile liquid. It can be used in all media, water, air, wastewater and soils. It is sometimes used combined with other agents to improve and accelerate processes. Some of its uses are listed below:

(i) About \(50\% \) of the world’s production of hydrogen peroxide is used for pulp- and paper bleaching. 

(ii) Diluted hydrogen peroxide mixed with aqueous ammonia is used to bleach human hair.

(iii) Hydrogen peroxide is used to remove new bloodstains.

(iv) \({{\rm{H}}_2}{{\rm{O}}_2}\) solution is used as an oxidant for rocket fuel and as a propellant for torpedoes and submarines.

(v) Hydrogen peroxide is used in aquaculture for controlling mortality caused by various microbes. 

(vi) It can be widely used to sanitize toothbrushes and sterilize makeup brushes.

(vii) Hydrogen peroxide is a mild antiseptic used on the skin to prevent infection of minor cuts, scrapes, and burns.

(viii) It may also be used as a mouth rinse to help remove mucus or to relieve minor mouth irritation.

(ix) Helps to treat plants with fungal infections and clears ponds filled with algae.

(x) It is used as an antichlor in the textile industry to remove excess chlorine after bleaching operations.

(xi) It is extensively used to manufacture inorganic chemicals like sodium perborate and percarbonate, which are essential constituents of good quality detergents.

(xii) It is used for restoring the colour of lead paintings that have blackened due to the action of \({{\rm{H}}_2}{\rm{S}}\) present in the air on lead paints.

Properties of Hydrogen Peroxide

The physical and chemical properties of hydrogen peroxide are given below:

Physical Properties of Hydrogen Peroxide

1. Hydrogen peroxide is a pale blue colour in an anhydrous form. It is an odourless thick syrupy liquid (due to \({\rm{H – }}\) bonding).

2. It has a bitter taste, causing blisters on the skin. 

3. It is soluble in water, alcohol, and ether.

4. Hydrogen peroxide is denser \(\left( {1.44\;{\rm{g}}/{\rm{c}}{{\rm{m}}^3}} \right)\) and more viscous than water. This is because molecules of \({{\rm{H}}_2}{{\rm{O}}_2},\) are strongly associated through \({\rm{H – }}\) bonds than \({{\rm{H}}_2}{\rm{O}}\) molecules.

5. Its boiling point is \({150^{\rm{o}}}{\rm{C,}}\) and thezing point is \( – {0.89^\circ }{\rm{C}}.\) The further increase in the boiling point of hydrogen peroxide is because, here, intermolecular hydrogen bonding is stronger than that of water.

6. The dipole moment of hydrogen peroxide is \({\rm{(2}}{\rm{.1 D)}}\) slightly more than water \((1.84{\rm{D}}).\)

7. Hydrogen peroxide is diamagnetic and has both polar and nonpolar bonds.

Table of Physical Properties

Property	Hydrogen Peroxide
Colour	Pale blue
Odour	Odourless
Taste	Bitter
Molecular Formula	\({{\rm{H}}_2}{{\rm{O}}_2}\)
Molecular weight	\({34.014\;{\rm{g/mol}}}\)
Solubility	Soluble in water, ether and alcohol
Density	\({1.44\;{\rm{g}}/{\rm{c}}{{\rm{m}}^3}}\)
Boiling Point	\(150{\,^{\rm{o}}}{\rm{C}}\)
Freezing Point	\(- 0.89{\,^{\rm{o}}}{\rm{C}}\)
Dipole Moment	\({\rm{2}}{\rm{.1}}\,{\rm{D}}\)
Magnetism	Diamagnetic

Chemical Properties of Hydrogen Peroxide

\({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}\) is a unique substance due to its molecular structure. It consists of atoms of oxygen in an oxidation state of \(-1\) unlike many substances, where oxygen occurs in an oxidation state of \(0\) or \(-2.\) This means that this substance can be used as both an oxidizing agent and a reducing agent, depending on the \({\rm{pH}}\) of its solution.

1. Decomposition

(a) Auto-oxidation and auto-reduction. 

Pure hydrogen peroxide is an unstable liquid. It decomposes into water and oxygen on long-standing or heating.

The decomposition is further accelerated by the presence of metals like platinum, gold, metal oxides \(\left( {{\rm{Mn}}{{\rm{O}}_2}} \right)\) or by certain metal ions such as \({\rm{F}}{{\rm{e}}^{{\rm{2 + }}}}\) ions. Even a rough surface favours its decomposition.

(b) Decomposition by exposure to light

\({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}\) is also decomposed by exposure to light. It is, hence, stored in wax-lined glass or plastic vessels in the presence of stabilizers like urea. 

2. Acidic Nature 

(a) Pure \({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}\) turns blue litmus red; hence, it is a weak acid. Its aqueous solution is neutral to litmus. Since its dissociation constant (\(1.55 \times {10^{ – 12}}\) at \(293\,{\rm{K}}\)) is slightly higher than that of \({{\rm{H}}_2}{\rm{O}}\left( {1.0 \times {{10}^{ – 14}}} \right),{{\rm{H}}_2}{{\rm{O}}_2}\) is only a slightly stronger acid than \({{\rm{H}}_{\rm{2}}}{\rm{O}}{\rm{.}}\) 

(b) \({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}\) ionizes as: 

Hence, \({{\rm{H}}_2}{{\rm{O}}_2}\) has two ionizable \({\rm{H – }}\)atoms, hence it forms two series of salts, i.e., hydroperoxides (acidic salts) and peroxides (normal salts). 

(c) The acidic nature of hydrogen peroxide is shown by its neutralization reactions with hydroxides and carbonates. 

\({\rm{NaOH}} + {{\rm{H}}_2}{{\rm{O}}_2} \to {\rm{NaH}}{{\rm{O}}_2}{\rm{(Sodium}}\,{\rm{hydroperoxide)}} + {{\rm{H}}_2}{\rm{O}}\)

\(2{\rm{NaOH}} + {{\rm{H}}_2}{{\rm{O}}_2} \to {\rm{N}}{{\rm{a}}_2}{{\rm{O}}_2}{\rm{(Sodium}}\,{\rm{peroxide)}} + 2{{\rm{H}}_2}{\rm{O}}\) 

\({\rm{Ba}}{({\rm{OH}})_2} + {{\rm{H}}_2}{{\rm{O}}_2} \to {\rm{Ba}}{{\rm{O}}_2} + 2{{\rm{H}}_2}{\rm{O}}\) 

3. Oxidising Property

\({{\rm{H}}_2}{{\rm{O}}_2}\) is a strong oxidizing agent as it accepts the electron easily and gets reduced in alkaline and acidic mediums. 

In an acidic medium

\({{\rm{H}}_2}{{\rm{O}}_2}\) can accept electrons and act as an oxidizing agent in the presence of an acidic medium. \({{\rm{H}}_2}{{\rm{O}}_2}\) is reduced to \({{\rm{H}}_2}{\rm{O}}{\rm{.}}\) 

\({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}{\rm{ + 2}}{{\rm{H}}^{\rm{ + }}}{\rm{ + 2}}{{\rm{e}}^{\rm{ – }}} \to {\rm{2}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\quad \left( {{{\rm{E}}^{\rm{o}}}{\rm{ = + 1}}{\rm{.77\;V}}} \right)\)

1. It oxidizes acidified ferrous sulphate to ferric sulphate.

\({\rm{2F}}{{\rm{e}}^{{\rm{2 + }}}}{\rm{(aq) + }}{{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}{\rm{(aq) + 2}}{{\rm{H}}^{\rm{ + }}}{\rm{(aq)}} \to {\rm{2F}}{{\rm{e}}^{{\rm{3 + }}}}{\rm{(aq) + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O(l)}}\)

2. It liberates iodine from acidified potassium iodide solution.

\({\rm{2}}{{\rm{I}}^{\rm{ – }}}{\rm{(aq) + }}{{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}{\rm{(aq) + 2}}{{\rm{H}}^{\rm{ + }}}{\rm{(aq)}} \to {{\rm{I}}_{\rm{2}}}{\rm{(s) + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O(l)}}\)

3. The orange-coloured solution of ice-cold acidified potassium dichromate and potassium chromate solution (containing ether) changes to blue on being oxidized by hydrogen peroxide. This reaction leads to the formation of chromium pentoxide \(\left( {{\rm{Cr}}{{\rm{O}}_{\rm{5}}}} \right)\) which dissolves in ether, producing a blue colouration.

Chromium pentoxide is actually a peroxide. Its structure is as follows –

4. It oxidizes \({\rm{Hg}}\) to \({\rm{HgO}}{\rm{.}}\)

\({\rm{Hg}} + {{\rm{H}}_2}{{\rm{O}}_2} \to {\rm{HgO}} + {{\rm{H}}_2}{\rm{O}}\)

5. Hydrogen sulphide is oxidized to sulphur in the presence of \({{\rm{H}}_2}{{\rm{O}}_2}.\)

\({{\rm{H}}_2}\;{\rm{S}} + {{\rm{H}}_2}{{\rm{O}}_2} \to 2{{\rm{H}}_2}{\rm{O}} + {\rm{S}}\)

In an alkaline medium

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

\({{\rm{H}}_2}{{\rm{O}}_2} + {\rm{O}}{{\rm{H}}^ – } + 2{e^ – } \to 3{\rm{O}}{{\rm{H}}^ – }\)

For example-

1. Brownish sediment is obtained when hydrogen peroxide oxidizes manganese salts to manganese dioxide. 

\({\rm{M}}{{\rm{n}}^{{\rm{2 + }}}}{\rm{(aq) + }}{{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}{\rm{(aq) + 2O}}{{\rm{H}}^{\rm{ – }}}{\rm{(aq)}} \to {\rm{Mn}}{{\rm{O}}_{\rm{2}}}{\rm{(s) + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O(l)}}\)

Hydrogen peroxide also oxidizes ferrous salts to ferric salts in an alkaline medium.

\({\rm{2\;F}}{{\rm{e}}^{{\rm{2 + }}}}{\rm{(aq) + }}{{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}{\rm{(aq)}} \to {\rm{2\;F}}{{\rm{e}}^{{\rm{3 + }}}}{\rm{(aq) + 2O}}{{\rm{H}}^{\rm{ – }}}{\rm{(aq)}}\)

2. The dark green colour of chromium sulphate changes to yellow coloured sodium chromate on being oxidized by hydrogen peroxide in an alkaline medium.

\({\rm{C}}{{\rm{r}}_2}{\left( {{\rm{S}}{{\rm{O}}_4}} \right)_3} + 3{{\rm{H}}_2}{{\rm{O}}_2} + 10{\rm{NaOH}} \to 2{\rm{N}}{{\rm{a}}_2}{\rm{Cr}}{{\rm{O}}_4} + 3{\rm{N}}{{\rm{a}}_2}{\rm{S}}{{\rm{O}}_4} + 8{{\rm{H}}_2}{\rm{O}}\)

3. It oxidizes formaldehyde \(\left( {{\rm{HCHO}}} \right)\) to formic acid \(\left( {{\rm{HCOOH}}} \right).\)

\({\rm{HCHO}} + {{\rm{H}}_2}{{\rm{O}}_2} \to {\rm{HCOOH}} + {{\rm{H}}_2}{\rm{O}}\)

4. It oxidises benzene to phenol in an alkaline medium.

\({{\rm{C}}_6}{{\rm{H}}_6} + {{\rm{H}}_2}{{\rm{O}}_2} \to {{\rm{C}}_6}{{\rm{H}}_5}{\rm{OH}} + {{\rm{H}}_2}{\rm{O}}\)

In neutral medium

Hydrogen peroxide oxidizes many compounds in a neutral medium. For example:

1. It oxidizes sulphites to sulphates.

\({\rm{SO}}_3^{2 – } + {{\rm{H}}_2}{{\rm{O}}_2} \to {\rm{SO}}_4^{2 – } + {{\rm{H}}_2}{\rm{O}}\)

2. It oxidizes nitrites to nitrates.

\({\rm{NO}}_2^ – + {{\rm{H}}_2}{{\rm{O}}_2} \to {\rm{NO}}_3^ – + {{\rm{H}}_2}{\rm{O}}\)

3. It oxidizes \({\rm{PbS}}\) (black) to lead sulphate (white)

\({{\rm{S}}^{2 – }} + 4{{\rm{H}}_2}{{\rm{O}}_2} \to {\rm{SO}}_4^{2 – } + 4{{\rm{H}}_2}{\rm{O}}\)

This reaction is used in restoring the white colour of lead paintings which have been blackened due to the formation of lead sulphide by the action of \({{\rm{H}}_{\rm{2}}}{\rm{S}}\) present in the air. On treatment with \({{\rm{H}}_2}{{\rm{O}}_2}\) Lead sulphide (black) changes into lead sulphate (white), and thus, the colour of lead paint is restored.

4. Reducing Property

In the presence of strong oxidizing agents, hydrogen peroxide behaves as a reducing agent both in acidic and alkaline mediums. In all these reactions, molecular oxygen is always produced by the combination of \({{\rm{H}}_2}{{\rm{O}}_2}\) with the nascent oxygen \([{\rm{O}}]\) released by the strong oxidizing agent.

\({{\rm{H}}_2}{{\rm{O}}_2} + [{\rm{O}}]\,{\rm{(From}}\,{\rm{oxidising}}\,{\rm{agent)}} \to {{\rm{H}}_2}{\rm{O}} + {{\rm{O}}_2}\)

In acidic medium

In an acidic medium, hydrogen peroxide gives up electrons and is oxidized to \({{\rm{O}}_2}.\)

\({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}\left( {{\rm{O}}.{\rm{S = }}\,{\rm{ – 1}}} \right) \to {\rm{2}}{{\rm{H}}^{\rm{ + }}}{\rm{ + }}{{\rm{O}}_{\rm{2}}}\left( {{\rm{O}}.{\rm{S}}\,{\rm{ = }}\,{\rm{0}}} \right){\rm{ + 2}}{{\rm{e}}^{\rm{ – }}}{\mkern 1mu} \left[ {{\rm{Oxidation}}} \right]\)

For example-

1. \({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}\) reduces pink coloured acidified potassium permanganate solution to colourless.

\(2{\rm{KMn}}{{\rm{O}}_4} + 3{{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4} + 5{{\rm{H}}_2}{{\rm{O}}_2} \to {{\rm{K}}_2}{\rm{S}}{{\rm{O}}_4} + 2{\rm{MnS}}{{\rm{O}}_4} + 8{{\rm{H}}_2}{\rm{O}} + 5{{\rm{O}}_2}\)

2. Orange colour of \({{\rm{K}}_2}{\rm{C}}{{\rm{r}}_2}{{\rm{O}}_7}\) changes to green coloured chromium salt due to its reduction by hydrogen peroxide.

\({\rm{C}}{{\rm{r}}_{\rm{2}}}{\rm{O}}_{\rm{7}}^{{\rm{2 – }}}{\rm{(aq) + 8}}{{\rm{H}}^{\rm{ + }}}{\rm{(aq) + 3}}{{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}} \to {\rm{2C}}{{\rm{r}}^{{\rm{3 + }}}}{\rm{(aq) + 7}}{{\rm{H}}_{\rm{2}}}{\rm{O(l) + 3}}{{\rm{O}}_{\rm{2}}}{\rm{(g)}}\)

3. It reduces manganese dioxide to manganese sulphate in the presence of dilute sulphuric acid.

\({\rm{Mn}}{{\rm{O}}_{\rm{2}}}{\rm{(aq) + 2}}{{\rm{H}}^{\rm{ + }}}{\rm{(aq) + }}{{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}} \to {\rm{M}}{{\rm{n}}^{{\rm{2 + }}}}{\rm{(aq) + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O(l) + }}{{\rm{O}}_{\rm{2}}}{\rm{(g)}}\)

4. It reduces ozone to dioxygen.

\({{\rm{O}}_3} + {{\rm{H}}_2}{{\rm{O}}_2} \to {{\rm{H}}_2}{\rm{O}} + 2{{\rm{O}}_2}\)

5. Chlorine and bromine are reduced to \({\rm{HCl}}\) and \({\rm{HBr}}\) respectively. This Property is called Antichlor.

\({\rm{B}}{{\rm{r}}_2} + {{\rm{H}}_2}{{\rm{O}}_2} \to 2{\rm{HBr}} + {{\rm{O}}_2}\)

In alkaline medium

In an alkaline medium, hydrogen peroxide is oxidized to \({{\rm{O}}_{\rm{2}}}{\rm{.}}\)

\({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}{\rm{ + }}\,{\rm{2O}}{{\rm{H}}^{\rm{ – }}} \to {\rm{2}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\,{\rm{ + }}\,{{\rm{O}}_{\rm{2}}}{\rm{ + }}\,{\rm{2e}}\)

For example-

1. Purple coloured solution of potassium permanganate is reduced to brown coloured manganese dioxide by hydrogen peroxide in alkaline solution.

\({\rm{2KMn}}{{\rm{O}}_{\rm{4}}}{\rm{(aq) + 3}}{{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}{\rm{(aq)}} \to {\rm{2Mn}}{{\rm{O}}_{\rm{2}}}{\rm{(\;s) + 2KOH(aq) + 3}}{{\rm{O}}_{\rm{2}}}{\rm{(\;g) + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O(l)}}\)

2. It reduces ferric salts to ferrous salts.

\({\rm{2F}}{{\rm{e}}^{{\rm{3 + }}}}{\rm{(aq) + }}{{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}{\rm{(aq) + 2O}}{{\rm{H}}^{\rm{ – }}}{\rm{(aq)}} \to {\rm{2F}}{{\rm{e}}^{{\rm{2 + }}}}{\rm{(aq) + }}{{\rm{O}}_{\rm{2}}}{\rm{(g) + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O(l)}}\)

3. It reduces alkaline potassium ferricyanide to potassium ferrocyanide.

\({\rm{2}}{\left[ {{\rm{Fe(CN}}{{\rm{)}}_{\rm{6}}}} \right]^{{\rm{3 – }}}}{\rm{(aq) + 2O}}{{\rm{H}}^{\rm{ – }}}{\rm{(aq) + }}{{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}{\rm{(aq)}} \to {\rm{2}}{\left[ {{\rm{Fe(CN}}{{\rm{)}}_{\rm{6}}}} \right]^{{\rm{4 – }}}}{\rm{(aq) + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O(l) + }}{{\rm{O}}_{\rm{2}}}{\rm{(g)}}\)

4. It reduces hypohalites to halides in an alkaline medium.

\({\rm{NaOBr(Sodium}}\,{\rm{hypobromite)}} + {{\rm{H}}_2}{{\rm{O}}_2} \to {\rm{NaBr}} + {{\rm{H}}_2}{\rm{O}} + {{\rm{O}}_2}\)

\({\rm{CaOC}}{{\rm{l}}_2}{\rm{(Bleaching}}\,{\rm{powder)}} + {{\rm{H}}_2}{{\rm{O}}_2} \to {\rm{CaC}}{{\rm{l}}_2} + {{\rm{H}}_2}{\rm{O}} + {{\rm{O}}_2}\)

5. It reduces metal oxides to metals, i.e., silver oxide to silver in the alkaline medium. However, lead dioxide is reduced to lead monoxide.

\({\rm{A}}{{\rm{g}}_2}{\rm{O}} + {{\rm{H}}_2}{{\rm{O}}_2} \to 2{\rm{Ag}} + {{\rm{H}}_2}{\rm{O}} + {{\rm{O}}_2}\)

\({\rm{Pb}}{{\rm{O}}_2}({\rm{Lead}}\,{\rm{dioxide}}) + {{\rm{H}}_2}{{\rm{O}}_2} \to {\rm{PbO}}({\rm{Lead}}\,{\rm{oxide}}) + {{\rm{H}}_2}{\rm{O}} + {{\rm{O}}_2}\)

6. It reduces iodine to iodide ions in the basic medium.

\({{\rm{I}}_{\rm{2}}}\left( {\rm{s}} \right)\,{\rm{ + }}\,{{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}\left( {{\rm{aq}}} \right)\,{\rm{ + }}\,{\rm{2O}}{{\rm{H}}^{\rm{ – }}}\left( {{\rm{aq}}} \right) \to {\rm{2}}{{\rm{I}}^{\rm{ – }}}\left( {{\rm{aq}}} \right)\,{\rm{ + }}\,{\rm{2}}{{\rm{H}}_{\rm{2}}}{\rm{O}}({\rm{l}})\,{\rm{ + }}\,{{\rm{O}}_{\rm{2}}}\left( {\rm{g}} \right)\)

How does Hydrogen Peroxide Disinfection Work?

Among all other applications of hydrogen peroxide, \({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}\) is widely used as a disinfectant from treating inflamed gums to combating excessive microbial growth in water systems. Hydrogen peroxide reacts very fast to disintegrate into hydrogen and water without the formation of any by-product. The disinfection mechanism of hydrogen peroxide is based on the release of oxygen radicals, as shown below.

\({{\rm{H}}_2}{{\rm{O}}_2} \to {{\rm{H}}_2}{\rm{O}} + [{\rm{O}}]\)

This increases the amount of oxygen in the water. oxygen radicals decompose pollutants, and only water remains behind. radicals have both oxidizing and disinfecting abilities. Hydrogen peroxide eliminates proteins through oxidation.

The above reaction is also the cause behind hydrogen peroxide being used as a bleaching agent. The nascent oxygen released oxidizes the colouring matter to a colourless product (Bleaching action of \({{\rm{H}}_2}{{\rm{O}}_2}\)).

\({\rm{Colouring}}\,{\rm{matter}} + {\rm{[O]}} \to {\rm{Colourless}}\,{\rm{matter}}\)

Hydrogen peroxide is used to bleach delicate materials like ivory, silk etc.

How is Hydrogen Peroxide Prepared?

1. Laboratory preparation

In the laboratory, hydrogen peroxide can be prepared by any of the following methods.

1. From sodium peroxide (Merck’s Process): In this process, sodium peroxide is added to a dilute solution of sulphuric acid \(\left( {20\% } \right)\) surrounded by ice in small amounts with constant stirring. The solution, upon further cooling, gives crystals of \({\rm{N}}{{\rm{a}}_2}{\rm{S}}{{\rm{O}}_4}.\) \({\rm{10}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\) which can be removed by filtration. The solution is about \({\rm{30\% }}\) aqueous solution of hydrogen peroxide.

\({\rm{N}}{{\rm{a}}_2}{{\rm{O}}_2} + {{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4} \to {\rm{N}}{{\rm{a}}_2}{\rm{S}}{{\rm{O}}_4} + {{\rm{H}}_2}{{\rm{O}}_2}\)

2. From barium peroxide: A paste of hydrated barium peroxide \(\left( {{\rm{Ba}}{{\rm{O}}_{\rm{2}}}{\rm{.8}}{{\rm{H}}_{\rm{2}}}{\rm{O}}} \right)\) prepared in ice-cold water is treated with about \({20\% }\) ice-cold solution of sulphuric acid.  A white coloured precipitate of \({\rm{BaS}}{{\rm{O}}_4}\) is obtained, which is removed by filtration. The solution left is about \(5\% \,{{\rm{H}}_2}{{\rm{O}}_2}.\) 

\({\rm{Ba}}{{\rm{O}}_2} \cdot 8{{\rm{H}}_2}{\rm{O}} + {{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4} \to {\rm{BaS}}{{\rm{O}}_4}{\rm{(White}}\,{\rm{ppt)}} + {{\rm{H}}_2}{{\rm{O}}_2} + 8{{\rm{H}}_2}{\rm{O}}\)

The above process is not so economical because barium sulphate slowly forms a protective coating around \({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}\) and prevents it from taking part further in the chemical reaction. The \({\rm{B}}{{\rm{a}}^{{\rm{2 + }}}}\) ions present in the solution slowly cause the decomposition of hydrogen peroxide. Therefore, the solution cannot be stored for a long time. To check this, phosphoric acid is used in place of sulphuric acid. Barium phosphate formed gets completely precipitated, and in the absence of \({\rm{B}}{{\rm{a}}^{2 + }}\) ions, there is no danger of any decomposition of hydrogen peroxide.

\(3{\rm{Ba}}{{\rm{O}}_2} \cdot 8{{\rm{H}}_2}{\rm{O}} + 2{{\rm{H}}_3}{\rm{P}}{{\rm{O}}_4} \to {\rm{B}}{{\rm{a}}_3}{\left( {{\rm{P}}{{\rm{O}}_4}} \right)_2}({\rm{ppt}}) + 24{{\rm{H}}_2}{\rm{O}} + 3{{\rm{H}}_2}{{\rm{O}}_2}\)

3. Alternatively, carbon dioxide gas may be passed through hydrated barium peroxide paste in ice-cold water in a slow stream. The white precipitate of barium carbonate is filtered off, and the solution is almost \(15 – 20\% \) aqueous solution of hydrogen peroxide.

\({\rm{Ba}}{{\rm{O}}_2} + {\rm{C}}{{\rm{O}}_2} + {{\rm{H}}_2}{\rm{O}} \to {\rm{BaC}}{{\rm{O}}_{\rm{3}}}{\rm{(S) + }}{{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}{\rm{(I)}}\)

2. Industrial Preparation

1. By the electrolysis of a sulphuric acid solution

A \(50\% \) solution of sulphuric acid is electrolyzed in a cell. As a result, peroxodisulfuric acid is formed at the anode and hydrogen is evolved at the cathode.

\({{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4} \to {\rm{HSO}}_4^ – + {{\rm{H}}^ + }\)

At anode:

\({\rm{HSO}}_4^ – \to {{\rm{H}}_2}\;{{\rm{S}}_2}{{\rm{O}}_8}{\rm{(peroxo}}\,{\rm{disulphuric}}\,{\rm{acid) + 2}}{{\rm{e}}^{\rm{ – }}}\)

At cathode:

\({\rm{2}}{{\rm{H}}^{\rm{ + }}}{\rm{ + 2}}{{\rm{e}}^{\rm{ – }}} \to {{\rm{H}}_{\rm{2}}}\)

Peroxodisulfuric acid is taken out from the cell and is then hydrolyzed with water to give hydrogen peroxide, which is as follows-

\({{\rm{H}}_2}\;{{\rm{S}}_2}{{\rm{O}}_8} + 2{{\rm{H}}_2}{\rm{O}} \to 2{{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4} + {{\rm{H}}_2}{{\rm{O}}_2}\)

The solution obtained above is distilled under reduced pressure. Hydrogen peroxide distils while sulphuric acid with a high boiling point remains undistilled. The yield of hydrogen peroxide can be enhanced if a mixture of ammonium sulphate and sulphuric acid taken in equivalent amounts is electrolyzed.

Ammonium peroxodisulphate formed at the anode is withdrawn and is distilled with water to give hydrogen peroxide.

\({\left( {{\rm{N}}{{\rm{H}}_4}} \right)_2}\;{{\rm{S}}_2}{{\rm{O}}_8} + 2{{\rm{H}}_2}{\rm{O}} \to 2{\rm{N}}{{\rm{H}}_4}{\rm{HS}}{{\rm{O}}_4}{\rm{(Ammonium}}\,{\rm{hydrogen}}\,{\rm{sulphate)}} + {{\rm{H}}_2}{{\rm{O}}_2}\)

2. From 2-Ethyl anthraquinone

In the presence of a palladium catalyst, hydrogen gas is passed through 2-ethyl anthraquinone dissolved in benzene. It is reduced to \(2-\)ethyl anthraquinol.

Air is then passed through a mixture of \(2-\)ethyl anthraquinol, benzene and cyclohexanol. It is oxidized back to \(2-\)ethyl anthraquinone, and hydrogen peroxide is produced.

It is an example of alternate oxidation and reduction and is called auto-oxidation.

3. By oxidation of isopropyl alcohol 

Hydrogen peroxide acts as an initiator when a small amount of it is mixed with isopropyl alcohol. Oxygen is passed via the solution at about \({\rm{340}}\,{\rm{K}}\) with a little pressure. The oxidation reaction takes place because of which acetone and hydrogen peroxide are obtained.

\({\rm{C}}{{\rm{H}}_3}{\rm{CHOHC}}{{\rm{H}}_3}{\rm{(Isopropyl}}\,{\rm{alcohol)}} + {{\rm{O}}_2} \to {\rm{C}}{{\rm{H}}_3}{\rm{COC}}{{\rm{H}}_3}{\rm{(Acetone)}} + {{\rm{H}}_2}{{\rm{O}}_2}\)

Upon distillation, acetone and unreacted alcohol distil, leaving behind an aqueous solution of hydrogen peroxide.

Q.1. What is the difference between \(’20\) volume of hydrogen peroxide’ and \(’20\% \) aqueous solution of \({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}^{\rm{‘}}\)?
Ans: \(20\) volume of hydrogen peroxide means that \(1\) litre of hydrogen peroxide solution on decomposition will give \(20\) litres of oxygen at NTP whereas \(’20\% \) aqueous solution of \({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}\) means \({\rm{100}}\,{\rm{ml}}\) of the solution contains \({\rm{20}}\,{\rm{g}}\) of \({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}\) or \({\rm{20}}\,{\rm{g}}\) of \({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}\) are present in \({\rm{100}}\,{\rm{ml}}\) of the solution. Both are ways to express the strength of hydrogen peroxide.  In terms of the volume of \({{\rm{O}}_{\rm{2}}}\) (v/v) is VOLUME STRENGTH and as \({\rm{g/100}}\,{\rm{ml}}\) or \({\rm{g/litre(w/v)}}{\rm{.}}\) PERCENT STRENGTH, respectively.

Summary

Thus, we can conclude that hydrogen peroxide has a wide number of applications in our day-to-day life. But before using hydrogen peroxide, we need to check the expiration date. The extra oxygen breaks down over time, and once it loses its bubbles, it’s nothing more than water. We need to handle it carefully and avoid its exposure to sunlight. Also, care should be taken that it is not mistakenly ingested.

FAQs

Q.1. Is hydrogen peroxide safe to use?
Ans: Hydrogen peroxide is safe for most people if they use it correctly. However, the compound can be harmful if a person uses it too often or if the concentration is too strong. It is vital to use a concentration not stronger than 3% and use it in moderation to avoid irritation. Children should avoid handling hydrogen peroxide as there is a danger of them swallowing it.

Q.2. Does hydrogen peroxide kill germs?
Ans: Hydrogen peroxide is most effective when it is allowed to sit on surfaces for at least \(10\) minutes at room temperature. Hydrogen peroxide functions as a disinfectant by destroying essential components of germ cells and can deactivate a broad range of microorganisms, involving viruses, bacteria, fungi, and spores.
When it comes to reducing the germs in your home and containing the spread of Covid\(-19,\) hydrogen peroxide is a good option to utilize on inanimate surfaces like metal, glass, and plastics. This is according to the Centers for Disease Control (CDC).

Q.3. Is hydrogen peroxide stronger than bleach?
Ans: When we refer to bleach, it’s chlorine bleach, which contains sodium hypochlorite. Like hydrogen peroxide, bleach also releases nascent oxygen, which acts as a bleaching agent. Though bleach is stronger than hydrogen peroxide, it is quite a hazardous substance. It requires careful dilution for safe use, and this should only be with cold water. At the same time, hydrogen peroxide has a kinder environmental footprint and goes a long way in treating wastewater and disinfecting substances.

Q.4. Is it safe to brush your teeth with hydrogen peroxide?
Ans: When used correctly, oral care products with small amounts of hydrogen peroxide (conc. less than \(3\% \)) are safe and effective. However, prolonged use should be avoided to maintain teeth health. Hydrogen peroxide’s strong bleaching properties make it a common ingredient in teeth whitening products, especially in toothpaste. It dissolves the stains via an oxidation process.

Q.5. Will rinsing with peroxide whiten teeth?
Ans: Gargling with hydrogen peroxide may be an effective way to soothe a sore throat, disinfect our mouth and whiten our teeth. But it should be in diluted form. A higher concentration of hydrogen peroxide, if ingested, will cause internal damage to the organs accompanied by heavy bleeding. Ingestion should be avoided while rinsing with the diluted one too. However, to get whitened teeth with just gargling or rinsing will require prolonged usage.

Q.6. Can yellow teeth become white?
Ans: Yellow teeth can become white by using hydrogen peroxide. However, care should be taken while using it. If used incorrectly, i.e. in concentrations that are too high or if used too often, then it can cause serious and sometimes expensive tooth damage.

Q.7. What is the difference between rubbing alcohol and hydrogen peroxide?
Ans: Rubbing alcohol is chemically known as isopropyl alcohol. Though both are used for disinfecting purposes, rubbing alcohol is preferred over hydrogen peroxide. This is because rubbing alcohol is stronger than peroxide and is quite volatile. Peroxide is more harmful if it comes in contact with hands, but rubbing alcohol is much safer for cleansing hands. However, rubbing alcohol is highly flammable, whereas peroxide is not.

Q.8. Why is water so different from hydrogen peroxide?
Ans: The physical properties of water and hydrogen peroxide differ due to the difference in the extent of hydrogen bonding. The strength of hydrogen bonding is more in peroxide because peroxide consists of one additional oxygen atom than water, favouring more hydrogen bonding.
Chemical properties of water and hydrogen peroxide vary because of the strain in the \({\rm{O – O}}\) bond in hydrogen peroxide. The lone pairs on two oxygen atoms of hydrogen peroxide create a lot of strain which weakens the \({\rm{O – O}}\) bond, and it easily decomposes to water and oxygen. This is not the case with the water molecule. There is no \({\rm{O – O}}\) bond strain present in it.

Q.9. Can hydrogen peroxide form from hydrogen and water?
Ans: Hydrogen peroxide is not formed from hydrogen and water. It is prepared by treating metal peroxides like sodium peroxide, barium peroxide, etc., with ice-cold dilute acids to form hydrogen peroxide.

Q.10. Old paintings of lead are generally washed with a dilute solution of hydrogen peroxide to regain its colour. Why?
Ans: Black colour in lead paintings is due to the formation of \({\rm{PbS}}{\rm{.}}\) This is oxidized to lead sulphate using hydrogen peroxide.

Q.11. Between an acidic and basic solution of hydrogen peroxide, which is more stable?
Ans: Hydrogen peroxide is an unstable compound and decomposes into water and oxygen. It is more stable in the acidic medium than in the basic medium. The decomposition of hydrogen peroxide can be retarded by the addition of a small amount of acid.

Learn Hydrogen Peroxide Here

We hope this detailed article on hydrogen peroxide is helpful to you. If you have any queries on this page or in general about hydrogen peroxide, ping us through the comment box below and we will get back to you as soon as possible.