Ozone is an important topic included in the discussion of environmental issues. Ozone acts as an umbrella and restricts the entrance of harmful UV rays on the Earth’s surface. It is important for students to understand the significance of ozone and how it protects us from getting impacted by harmful rays from the sun. This article aims to discuss the significance, structure and causes of depletion of the ozone layer in detail.

CLEAR YOUR CONCEPTUAL DOUBTS ON OZONE

What Does Ozone Mean?

Ozone is an allotropic form of oxygen and exists as a triatomic molecule having the molecular formula \(\mathrm{O}_{3}\). Christian Friedrich Schonbein discovered it in \(1840.\) Ozone is present in the upper atmosphere about \(20\,{\rm{km}}\) above the surface of the Earth. It is believed that Ozone is formed by the action of ultraviolet rays coming from the sun on the oxygen present in the atmosphere.

As a result, the UV radiation that is harmful to humans is absorbed by oxygen, resulting in the formation of Ozone. The resulting Ozone layer also blocks the remaining ultraviolet rays from reaching the Earth’s surface. However, traces of Ozone can be found in the lower atmosphere.

Ozone Structure

Spectroscopic measurements point out that the Ozone is symmetrical but a bent molecule. The central oxygen atom in the Ozone is \({\rm{s}}{{\rm{p}}^2}\) hybridised, containing one lone pair of electrons. As a result, Ozone has an angular structure with a bond angle of \(117^\circ \) and O-O bond length is \(128\) pm.

The bond length in the Ozone molecule is intermediate between single and double bonds in oxygen atoms (single O-O bond = \(148\) pm, double O=O bond = \(121\) pm). Thus, the Ozone molecule is considered a resonance hybrid of the following two resonating structures (I) and (II).

Resonating Structures of Ozone

Ozone Depletion

The decrease in the quantity of Ozone in the upper atmosphere is called depletion of Ozone.

Ozone is formed in the upper atmosphere by a photochemical reaction involving oxygen. Ozone absorbs UV radiation between the wavelengths of 220-290 nm, protecting the Earth and its inhabitants from the harmful effects of ultraviolet radiation.

Therefore, the thick layer of Ozone is called the Ozone blanket. Without this protective Ozone layer, more ultraviolet radiation will reach the Earth’s surface, causing harm to plant and animal life. For example, increased UV radiation exposure can lead to skin cancer, immune system damage that leads to increased viral infections, damage to land plants and crops, and damage to sea plants and animals.

Ozone Depletion Causes

The balance of Ozone production and degradation has been disrupted due to the enhancement of Ozone degradation by chlorofluorocarbons \(\left( {{\rm{CFCs}}} \right).\)

1. Scientists discovered a hole in the Ozone blanket that covers the upper atmosphere near Antarctica in \(1980.\) All experts throughout the world are concerned about the Ozone layer depletion in the stratosphere. The hole in the Ozone layer is caused by the reaction of the Ozone with chlorofluorocarbons \(\left( {{\rm{CFCs}}} \right).\) These volatile chemicals have been used as aerosol propellants and refrigerants for a long time.

2. The release of nitrogen oxide \(\left(\mathrm{NO}_{2}\right)\) into the stratosphere by the exhaust system of supersonic jet aeroplanes also causes Ozone depletion. \({\rm{NO}}\) molecules can react with Ozone to give \({{\rm{O}}_2}.\)

\(\mathrm{NO}(\mathrm{g})+\mathrm{O}_{3}(\mathrm{~g}) \rightarrow \mathrm{NO}_{2}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g})\)

3. Atomic oxygen and reactive hydroxyl radicals, which are also abundant in the atmosphere due to biomass burning, destroy the Ozone layer in the stratosphere.

Harmful Effects of Ozone

If Ozone is present very near to the Earth’s surface due to the photochemical formation of smog, then it becomes harmful in the following ways:

1. Ozone is a poisonous gas having a chlorine-like smell and causes respiratory problems.
2. Ozone damages the tissues of plants.
3. Ozone causes damage to automobile tyres.

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Depletion of Ozone Hole

Depletion of Ozone makes the thick Ozone blanket thin. This depletion of Ozone is called an Ozone hole in the upper atmosphere.

Harmful Effects of Ozone Hole

Because of the Ozone hole in the upper atmosphere, the sun’s dangerous UV rays are not absorbed and reach the Earth in massive amounts. These rays will result in skin cancer as well as tissue damage in both animals and plants.

Properties of Ozone

Let us go through the different properties of Ozone:

Physical Properties of Ozone

1. Ozone is a pale blue gas with a characteristic pungent smell.
2. It is heavier than air.
3. Ozone is insoluble in water but soluble in turpentine oil and glacial acetic acid. 
4. The Ozone is diamagnetic. 
5. Ozone condenses to a deep blue liquid at \(- 112^\circ \,{\rm{C}}{\rm{.}}\)
6. Ozone solidifies at \(- 192.4^\circ \,{\rm{C}}{\rm{.}}\) Solidified Ozone has a black violet colour.

Study About Ozone Depletion

Chemical Properties of Ozone

1. Action with Litmus: Ozone is neutral towards litmus because it does not give any colour change with blue or red litmus.

2. Decomposition: Even at room temperature, pure Ozone decomposes to some amount. Decomposition speeds up as the temperature rises, becoming almost immediate at \(573\,{\rm{K}}.\)

3. Oxidising Properties of Ozone

Ozone is a powerful oxidising agent. It is a more potent oxidising agent than dioxygen. This is because Ozone can easily decompose to give an atom of nascent oxygen, which is more reactive than dioxygen.

\({{\rm{O}}_3} \to {{\rm{O}}_2} + {\rm{O}}\left( {{\rm{Atomic\;oxygen}}} \right)\)

(a) Oxidation of compounds: Ozone oxidises black lead sulphide to white lead sulphate.

(b) Oxidation of non-metals: Ozone oxidises non-metals such as sulphur, phosphorus or moist iodine to their oxyacids.

For example, Ozone oxidises sulphur to sulphuric acid.

(c) Oxidation of metals: Ozone oxidises certain metals such as silver, mercury, etc., to their respective oxides.

For example, Silver is oxidized to silver oxide.

4. Bleaching agent: Due to the oxidising action of Ozone, it acts as a light bleach and also as a sterilising agent. It acts as a bleaching agent for vegetable colouring matter.
For example, Ozone bleaches indigo, litmus, delicate fabrics, etc.

\({\rm{Vegetable\;Colouring\;matter}} + \;{{\rm{O}}_3}\; \to {\rm{Oxidised\;Coloured\;matter}} + \;{{\rm{O}}_2}\)

5. Formation of ozonides: Ozone reacts with alkenes in the presence of carbon tetrachloride to form an ozonide.

What is O₃ Used for?

1. It is used as a disinfectant and a germicide for water sterilisation due to its oxidising activity.
2. It can be used to bleach delicate fabrics, oils, starch, ivory, flour, and starch, among other things.
3. It is used to clean the air in crowded places such as movie theatres, subway stations, tunnels, mines, slaughterhouses, etc.
4. It is used as an oxidising agent in the production of artificial silk, synthetic camphor, potassium permanganate, and other similar products.
5. It is used to detect the position of a double bond in unsaturated organic compounds. 
6. It is used in the laboratory for the ozonolysis of organic compounds.

Ozone Therapy

Ozone therapy, sometimes known as “ozonotherapy,” is a long-established medical practice. A reactive form of oxygen called Ozone is given to the body to encourage a therapeutic effect. Though it is proven to be safe and has minimal side effects, there is a substantial dispute in the medical community over the usefulness of this therapy.

Uses of Ozone Therapy

Ozone therapy can be used to treat ischemic heart disease, macular degeneration, arthritis, and viral infections like HIV and SARS. It can also be used to disinfect wounds, activate the immune system, and treat cancer.

Side-effects of Ozone Therapy

When a person inhales Ozone gas, it irritates the lungs and throat, coughing, and increased asthma symptoms. High levels of exposure can cause lung damage and even death.

From this article, we can conclude that Ozone is the essential gas that protects Earth from harmful ultraviolet radiation coming from the sun. It has medical properties as well as many applications in industry, laboratory, commercial field, etc.

Summary

Ozone is an allotropic form of oxygen and exists as a triatomic molecule having the molecular formula \(\mathrm{O}_{3}\). Christian Friedrich Schonbein discovered it in \(1840.\) Ozone is present in the upper atmosphere about \(20\,{\rm{km}}\) above the surface of the Earth. Learn all the concepts on the ozone layer, its depletion, causes and ways to recover. You also learnt about the benefits and harm of ozone in our daily life. Finally, we answered some frequently asked questions on ozone topic.

PRACTICE QUESTIONS RELATED TO OZONE

Frequently Asked Questions (FAQs) on Ozone

Frequently asked questions related to ozone is listed as follows:

Q.1. Is Ozone bad for health?
Ans: Yes, Ozone is harmful to health. When a person inhales Ozone gas, it irritates the lungs and throat, coughing, and increases asthma symptoms. High levels of exposure can cause lung damage and even death.

Q.2. What is \(\mathrm{O}_{3}\) used for?
Ans: Following are the uses of Ozone –
a. It is used as a disinfectant and a germicide for water sterilisation due to its oxidising activity.
b. It can be used to bleach delicate fabrics, oils, starch, ivory, flour, and starch, among other things.
c. It is used to clean the air in crowded places such as movie theatres, subway stations, tunnels, mines, slaughterhouses, etc.
d. It is used as an oxidising agent in the production of artificial silk, synthetic camphor, potassium permanganate, and other similar products.

Q.3. What does Ozone mean?
Ans: Ozone is an allotropic form of oxygen and exists as a triatomic molecule having the molecular formula \(\mathrm{O}_{3}\). Ozone is an irritating bluish gas with a pungent smell utilised for oxidising, bleaching, disinfecting, and deodorising. Ozone is major air pollution in the lower atmosphere but a helpful component of the high atmosphere.

Q.4. What is the bad Ozone?
Ans: When ozone is present on the Earth’s surface, it is a very dangerous gas, which is why it is referred to as “bad.” 

Q.5. Where is Ozone found?
Ans: Ozone is present in the upper atmosphere about 20 km above the Earth’s surface, called the stratosphere.

Q.6. Name the Ozone-depleting substances.
Ans: Chlorofluorocarbons, nitrogen oxide, Atomic oxygen and reactive hydroxyl radicals are called Ozone-depleting substances.

Q.7. What is Ozone depletion?
Ans: Decrease of the quantity of Ozone in the upper atmosphere is called depletion of Ozone.

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