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Hydrogen Peroxide: Structure, Preparation and Chemical Properties


Have you ever noticed what laundrymen used to remove tough stains from the clothes in the past? Or how paper is made? 
The stains were not easily removed by the simple chemicals of the past. You will be surprised to know that laundrymen use a chemical named hydrogen peroxide to give whitening action to our clothes. And in pulp industry, it is used to bleach the materials of which paper is made, converting colored compounds to colorless compounds. Hydrogen peroxide is a versatile chemical consisting of myriad of applications.

Why do we Study this Concept?

Due to the numerous uses of hydrogen peroxide in our daily life, it is important to study about the properties and actions of this compound. Hydrogen peroxide acts as an oxidising agent in multiple ways such as hair colours and bleaches, toothpaste, mouthwashes, bathroom cleaners, and laundry stain removers, providing a lightening and whitening effect. 

Table of Contents

Chemistry of Hydrogen Peroxide

Louis Jacques in 1818 firstly isolated hydrogen peroxide. It is the simplest peroxide, with reactive oxygen species with a single oxygen–oxygen linkage. The chemical formula of Hydrogen peroxide is .

Structure of Hydrogen Peroxide

has a non-linear and non-planar structure. It exhibits an open-book structure. The linkage in is known as a peroxy linkage.The oxidation state of both the oxygens in is .The open-book structures of in the solid and the gaseous phase. In the gaseous phase, the structure of is much more open as compared to the structure in the solid phase. This is because of the presence of extensive hydrogen bonding in the solid phase that will cause the molecules to exhibit a congested structure.

                                               


Laboratory Preparation of Hydrogen Peroxide

1. Merck’s process: When a calculated amount of sodium peroxide is added to an ice cold dilute solution of 20% , it gives .
+  +  
 
2. Effects of sulphuric acid or phosphoric acid on hydrated barium peroxide: Acidifying hydrated barium peroxide and removing excess water by evaporation under reduced pressure gives hydrogen peroxide. The reaction of hydrated barium peroxide  with sulphuric acid is given as follows:
+ + +

Industrial Preparation of Hydrogen Peroxide

1. By the electrolysis of 50% solution:
The electrolysis of 50% solution generates peroxydisulphuric acid at anode.

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The hydrolysis of peroxydisulphuric acid gives .

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2. By auto-oxidation of :
Industrially, is prepared by the auto-oxidation of .

Physical Properties of Hydrogen Peroxide 

  • In a pure state at STP conditions, is almost a colourless syrupy liquid. However, in thick layers, it gives a pale blue tinge.
  • In a pure state at STP conditions, it freezes at –0.5 °C and has a density of 1.4 g (i.e., has a greater density than ).
  • It is diamagnetic in nature.
  • has extensive hydrogen bonding than water. Hence, is an associated liquid due to hydrogen bonding.
  • It is a better polar solvent than water. However, most of the reactions use water as a solvent compared to hydrogen peroxide due to the abundance of water. Also, water has a greater stability than hydrogen peroxide.
  • Its dipole moment is 2.1 D.
  • has a strong auto-oxidation ability.

Chemical Properties 

1. Decomposition of : Pure is an unstable liquid. It decomposes into water and oxygen either upon standing or upon heating.

Above reaction is an example of a disproportionation reaction.

2. Oxidising nature of :   is a powerful oxidising agent. It acts as an oxidising agent in neutral, acidic and alkaline mediums.

3. Reducing nature of :  is likely to take oxygen from strong oxidising agents and acts as a reducing agent. 
 Oxygen has an oxidation state of −1 in. In the presence of some oxidising agents,  converts to and . Since has zero oxidation state, we can say that oxidised to . It acts as a reducing agent in neutral, acidic and alkaline mediums.

4. Bleaching action of Due to the oxidising nature of, it can act as a bleaching agent. can be used to bleach delicate materials like ivory, silk, wool, and leather, etc. The bleaching action of hydrogen peroxide is permanent. This is due to the oxidation by nascent oxygen.

Colouring matter + → Colourless matter.

Uses of Hydrogen Peroxide

Major applications of are given as follows:

  • It is used to bleach delicate articles like wool, hair, feather, ivory, etc.
  • It is used as an aerating agent in the production of sponge rubber.
  • It is used to restore the colour of old lead paintings.
  • It is used as an antiseptic and germicide to wash wounds, teeth, and ears, under the name of Perhydrol.

Practice Problems on Hydrogen Peroxide

Q 1: What do you understand by ‘100 volume’ of ?
Answer:
'100 volume' hydrogen peroxide is sold as a 30 percent solution of. At STP, one millilitre of 30 percent solution produces 100 millilitres of oxygen.

Q 2: 100 of a given sample of   is labeled as . Its percentage strength is:
A. 10 % (w/v)
B. 22.4 % (w/v)
C. 13.6% (w/v)
D. 44.8% (w/v)
Answer:
(C) 13.6% (w/v)
means one liter of this sample of on decomposition gives of gas at Therefore, 100 or 100 gives 4500 or of gas.


 By the disproportionation reaction one mole of gives half mol of gas.
Therefore moles of =

Weight of =

Thus,  (w/v) concentration = 13.6%

Q 3: Which of the following statement is incorrect about hydrogen peroxide?

A. It is stored in plastic bottles in the dark.|
B. It can act as an oxidising agent as well as a reducing agent.
C. It is used as a bleaching agent.
D. It has acidic as well as basic properties towards the litmus.

Answer: (D)
decomposes slowly on exposure to light. Hence, it is stored in dark bottles. It acts as both oxidising agent as well as a reducing agent. One of the most common uses of is that it is used as bleaching agent.  is almost neutral towards the litmus test so option (D) is not correct.

Q 4: How can dilute be concentrated to 50%?
A. Distillation under reduced pressure
B. Using vacuum desiccator
C. Slow evaporation on a water bath
D. Cooling it to in a cold bath of ether and dry ice

Answer: (C)
Dilute can be concentrated to about 50% by slow evaporation in a water bath.

FAQs on Hydrogen Peroxide

Q 1. Does hydrogen peroxide burn?
Answer:
No, hydrogen peroxide itself does not burn. However, hydrogen peroxide above 60 wt.% is classified as an oxidizer. Hydrogen peroxide may cause a fire if it comes in contact with combustible material.

Q 2. What is the formula of volume strength of ?

Answer: Volume strength of = Molarity × 11.2 = Normality × 5.6

Q 3. Is used as a rocket propellant?

Answer: High-concentration  is referred to as "high-test peroxide" (HTP). It can be used either as a monopropellant (not mixed with fuel) or as the oxidizer component of a bipropellant rocket. Use as a monopropellant takes advantage of the decomposition of 70–98% concentration hydrogen peroxide into steam and oxygen. The propellant is pumped into a reaction chamber, where a catalyst, usually a silver or platinum screen, triggers decomposition, producing steam, which is expelled through a nozzle, generating thrust.

Q 4. Which kind of impurities are present in hydrogen peroxide solutions?

Answer: Compared to other chemicals even standard grades of hydrogen peroxide exhibit excellent purity (>99.9 percent). This is based on highly sophisticated production processes including purification steps. Other than the stabilizer package, impurities are mostly expressed as total organic carbon, at levels of milligrams per litre. Most other impurities like anions or heavy metals are well below standard detection limits.

Related Topics on Hydrogen Peroxide
 

Ortho and parahydrogen Hydrogen bonding
Hydrogen Hardness of water
Heavy Water Deuterium
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