Hydrogen Peroxide

You just cut your finger, and what should you do? You went to that brown bottle of hydrogen peroxide in the medicine cabinet. When it starts to fizz and bubble, you probably wonder, "What is going on here, anyway?" Among the many family chemicals around is hydrogen peroxide; by nature, it disinfects the wounds, whitens teeth, and cleans surfaces. It is a simple compound, with only two atoms of hydrogen bonded to two atoms of oxygen, yet it is involved in a multitude of chemical and biological reactions.

This Story also Contains

1. Hydrogen Peroxide(H2O2) - Methods of Preparation
2. Physical Properties of H2O2
3. Various physical properties of hydrogen peroxide are as follows:
4. Chemical Properties of H₂O₂
5. Some Solved Examples
6. Summary

This paper will explore the rather interesting world within the kingdom of hydrogen peroxide. We will explore the physical properties that automatically make this single substance diversified for so many uses. Let us now delve into its chemical properties to detail some of the reactions and behaviours of H₂O₂ that allow it to realize those many functions. By the end of this paper, you will be well versed in hydrogen peroxide, starting from the molecular structure to its use in everyday life and scientific processes.

Hydrogen Peroxide(H₂O₂) - Methods of Preparation

Hydrogen peroxide is an important chemical used in pollution control treatment of domestic and industrial effluents.
It can be prepared by the following methods.

• Acidifying barium peroxide and removing excess water by evaporation under reduced pressure gives hydrogen peroxide.$\mathrm{BaO}_2 \cdot 8 \mathrm{H}_2 \mathrm{O}(\mathrm{s})+\mathrm{H}_2 \mathrm{SO}_4(\mathrm{aq}) \rightarrow \mathrm{BaSO}_4(\mathrm{~s})+\mathrm{H}_2 \mathrm{O}_2(\mathrm{aq})+8 \mathrm{H}_2 \mathrm{O}(\ell)$
• Peroxodisulphate, obtained by electrolytic oxidation of acidified sulphate solutions at high current density, on hydrolysis yields hydrogen peroxide.
  $2 \mathrm{HSO}_4^{-}(\mathrm{aq}) \xrightarrow{\text { Electrolysis }} \mathrm{HO}_3 \mathrm{SOOSO}_3 \mathrm{H}(\mathrm{aq}) \xrightarrow{\text { Hydrolysis }} 2 \mathrm{HSO}_4^{-}(\mathrm{aq})+2 \mathrm{H}^{+}(\mathrm{aq})+\mathrm{H}_2 \mathrm{O}_2(\mathrm{aq})$
• Industrially it is prepared by the autooxidation of 2-alklylanthraquinols.
  2 - ethylanthraquinol $\rightleftharpoons \mathrm{H}_2 \mathrm{O}_2+$ (Oxidised product)
  In this case, 1% H₂O₂ is formed. It is extracted with water and concentrated to ~30% (by mass) by distillation under reduced pressure. It can be further concentrated to ~85% by careful distillation under low pressure. The remaining water can be frozen out to obtain pure H₂O₂.

Physical Properties of H₂O₂

Pure hydrogen peroxide is a pale blue liquid; however, it is colourless in dilute solutions. It has slightly more viscosity compared to water and this makes it produce a thicker solution. The chief physical properties of H₂O₂ include its boiling point, which lies around 150.2°C or 302.4°F. In this context, the high boiling point corresponds to the strong hydrogen bonds that exist between molecules.

Another interesting property of this compound is the density of approximately 1.45 gcm³ at 25°C, hence slightly more dense compared to water; that is to say, the volume weight of hydrogen peroxide is more than that of water. It is also highly soluble in water hence easily utilizable in solutions of water for various applications.

Hydrogen peroxide decomposes exothermically into water and oxygen gas; the reaction can be catalyzed by light, heat, or certain chemicals. This property of decomposition underlies many practical applications in the sphere of cleaning, disinfection, bleaching, and rocket propulsion.

Physical Properties of H₂O₂

Various physical properties of hydrogen peroxide are as follows:

• Pure anhydrous hydrogen peroxide is a syrupy liquid. It is colourless but gives a bluish tinge in thick layers. It is odourless.
• Its specific gravity is 1.45 at 0^oC.
• It is soluble in water, alcohol and ether.
• It has a bitter taste. It is injurious to the skin.
• It boils at 152^oC and freezes at -0.89^oC. It begins to decompose at boiling point, however, it can be distilled under reduced pressure.
• It is an associated liquid due to hydrogen bonding.
• The dipole moment of H₂O₂ is a little more than that of H₂O.

Chemical Properties of H₂O₂

Chemically, hydrogen peroxide is one of the strongest oxidizing agents and will receive electrons in a reaction. From this comes the ability of hydrogen peroxide to be a very effective breaking organic matter compound and killing bacteria, viruses, and fungi, hence being commonly applied in disinfection.

Sometimes hydrogen peroxide can behave both as an oxidizing and reducing agent, depending on the reaction conditions or reactants of the set-up. Whereas in an acidic medium, it acts as an oxidizing agent, this transforms into one of the reducing agents in a basic medium. This is based on the formation of hydroxyl radicals and other reactive species of oxygen from the hydrogen peroxide.

One of the most common reactions of hydrogen peroxide is its decomposition into water and oxygen:

$2 H₂O₂ → 2 H₂O + O₂$

In the cell, this is typically catalyzed by enzymes such as catalase, which assists the cells in fighting against oxidative stress. Then catalysts, for example, manganese dioxide or potassium iodide are employed to tune the rate of decomposition.

Relevance and Applications of Hydrogen Peroxide

Other uses of hydrogen peroxide are in the health sector, where it is applied to disinfect surgical instruments and clean hospital surfaces. It possesses the property of bactericidal activity, thereby forming a highly important tool in maintaining hygiene and preventing infections.

• Stability: It is unstable. It decomposes on standing and heating. It is an example of an auto oxidation-reduction reaction.$2 \mathrm{H}_2 \mathrm{O}_2 \rightleftharpoons 2 \mathrm{H}_2 \mathrm{O}+\mathrm{O}_2$
• Acidic nature: The pure liquid has a weak acidic nature but its aqueous solution is neutral towards litmus. It reacts with alkalis and carbonates to give their corresponding peroxides.$\mathrm{H}_2 \mathrm{O}_2+2 \mathrm{NaOH} \rightarrow \mathrm{Na}_2 \mathrm{O}_2+2 \mathrm{H}_2 \mathrm{O}$
• Oxidising nature: It is a powerful oxidising agent. It is an electron acceptor in acidic and alkaline solutions.
  $\mathrm{H}_2 \mathrm{O}_2+2 \mathrm{H}^{+}+2 \mathrm{e}^{-} \rightarrow 2 \mathrm{H}_2 \mathrm{O} \quad$ (In acidic medium) $\mathrm{H}_2 \mathrm{O}_2+2 \mathrm{e}^{-} \rightarrow 2 \mathrm{OH}^{-} \quad$ (In alkaline medium)
• Reducing nature: H₂O₂ can also act as a reducing agent towards powerful oxidising agents.
  $\mathrm{H}_2 \mathrm{O}_2 \rightarrow 2 \mathrm{H}^{+}+\mathrm{O}_2+2 \mathrm{e}^{-}$
  In an alkaline medium, its reducing agent is more effective.$\mathrm{H}_2 \mathrm{O}_2+2 \mathrm{OH}^{-} \rightarrow 2 \mathrm{H}_2 \mathrm{O}+\mathrm{O}_2+2 \mathrm{e}^{-}$
• H₂O₂ decomposes slowly on exposure to light. ,
  $2 \mathrm{H}_2 \mathrm{O}_2(\mathrm{l}) \rightarrow 2 \mathrm{H}_2 \mathrm{O}(\mathrm{l})+\mathrm{O}_2(\mathrm{~g})$
• In the presence of metal surfaces or traces of alkali (present in glass containers), the above reaction is catalysed. It is, therefore, stored in wax-lined glass or plastic vessels in the dark. Urea can be added as a stabiliser.
• It is kept away from dust because dust can induce explosive decomposition of the compound.

Recommended topic video on (Hydrogen peroxide)

Some Solved Examples

Example 1

Question:

In the Merck's process for formation of $H(_2)O(_2)$, the following reaction (unbalanced) takes place:

${mBaO_2 + n CO_2 + pH_2O \rightarrow A+ H_2O_2}$

Out of the following, A could be:

1. BaO

2. $H(_2)CO(_3)$

3. $BaCO(_3)$

4. $Ba(HCO(_3))(_2)$

Solution:

In Merck's process, $H(_2)O(_2)$ is obtained by passing a current of $CO(_2)$through a solution of barium peroxide. The reaction involved in Merck's process is:

${BaO_2 + CO_2 + H_2O \rightarrow BaCO_3 + H_2O_2} $

Hence, the answer is option (3): BaCO(_3).

Example 2

Question:

Which of the following is true about the production of hydrogen peroxide from barium peroxide?

1. Anhydrous Barium peroxide is used.

2. $Ba(SO(_4))(_2)$ is formed as a byproduct.

3. $H(_2)SO(_4)$ is used to carry out the conversion.

4. Excess water is removed by boiling.

Solution:

Hydrogen peroxide is produced by treating Barium Peroxide with $H(_2)SO(_4)$

${BaO_2. 8H_2O + H_2SO_4 \rightarrow BaSO_4 + 8H_2O + H_2O_2}$

Hydrated Barium Peroxide is used, and $BaSO(_4)$ forms a protective layer on barium peroxide, slowing the reaction. The excess water is removed by evaporation under reduced pressure. Hence, the answer is option (3): $H(_2)SO(_4) $is used to carry out the conversion.

Example 3

Question:

A 20.0 mL solution containing 0.2 g of impure $H(_2)O(_2)$ reacts completely with 0.316 g of $KMnO(_4)$ in acidic solution. The purity of $H(_2)O(_2)$ (in %) is _________. (Mol. wt. of $H(_2)O(_2) $= 34, mol. wt. of KMnO(_4) = 158)

Solution:

The reaction is:

${H_2O_2 + KMnO_4 \rightarrow Mn^{+2} + O_2} $

In the balanced reaction:

- Electron transfer of $H(_2)O(_2)$ (n) = 2 (Oxygen: -2 to 0)

- Electron transfer of $KMnO(_4)$ (n) = 5 (Mn: +7 to +2)

Using the formula:

${Number of Eq. of } {H_2O_2}$ = ${Number of Eq. of } {KMnO_4} ]$

$ {Mole} \times n{-factor}) { of H_2O_2}$ =$ {Mole} \times n{-factor}) { of KMnO_4} ]$

$[ x \times 2 = \frac{0.316}{158} times 5 ]$

$[ x = 5 \times 10^{-3} { mol} ]$

Now,

${Mass} = {Mole} \times {Molar mass}$

${mass}_{H_2O_2} = 5 \times 10^{-3} \times 34 = 0.17 gm$

Purity:

% purity = $\frac{mass of pure product}{mass of impure product obtained} \times 100 % $

$ \text{purity of } \mathrm{H_2O_2} = \frac{0.17}{0.2} \times 100 = 85 \% $

Hence, the answer is option (1): 85.

Summary

Hydrogen peroxide is applied to a majority of aspects, from household disinfectants, and industrial processes to its usefulness in scientific research. It has several special physical and chemical properties, like the fact that it can act either way as an oxidizing or a reducing agent. The substance is thus very versatile and of great value. The properties and reaction effects of hydrogen peroxide enunciate its practical usage, which became crucial in everyday life, but also in advanced technology or environmental applications.