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Ozone – Properties, Structure, Preparation, Reactions and Uses

  • Last Updated : 31 Dec, 2021

Ozone is an irritating light blue gas that, even at low concentrations, is explosive and poisonous. It naturally occurs in small levels in the Earth’s stratosphere, where it absorbs solar UV light, which would otherwise cause severe harm to living things on the Earth’s surface. Under some conditions, photochemical reactions in the lower atmosphere between nitrogen oxides and hydrocarbons can produce ozone in concentrations high enough to irritate the eyes and mucous membranes.

Ozone is a triatomic oxygen allotrope that gives the air a distinctive odour after a thunderstorm or near electrical equipment. The odour of ozone surrounding electrical machinery was first reported in 1785, and the chemical composition of ozone was identified in 1872.


The odour of ozone is similar to that of chlorine and may be detected by many people in quantities as low as 0.1 ppm in the air. In 1865, the structure of ozone was discovered. Later, it was discovered that the molecule has a bent shape and is mildly paramagnetic. Under normal conditions, ozone is a pale blue gas that condenses to a dark blue liquid and then to a violet-black solid at cryogenic temperatures. Ozone’s incompatibility with more prevalent dioxygen causes both concentrated gas and liquid ozone to break down explosively under high temperatures, physical trauma, or rapid warming to the boiling point. As a result, it is only utilised commercially in low amounts.

Ozone is a potent oxidant (much more potent than dioxygen) with numerous industrial and consumer applications involving oxidation. Above concentrations of roughly 0.1 ppm, ozone’s high oxidizing potential leads it to harm mucous and respiratory tissues in animals, as well as tissues in plants. While this makes ozone a substantial respiratory hazard and pollutant near the ground, a higher ozone layer concentration (from two to eight ppm) is beneficial because it keeps harmful UV rays from reaching the Earth’s surface.

Physical Properties of Ozone

  1. Ozone is a colourless or pale blue gas that is mildly soluble in water but much more soluble in inert nonpolar solvents like carbon tetrachloride or fluorocarbons, where it forms a blue solution.
  2. It condenses to create a dark blue liquid around 161K.
  3. Allowing this liquid to reach its boiling point is dangerous since both concentrated gaseous and liquid ozone has the potential to explode.
  4. At temperatures below 80 degrees Celsius, it solidifies as a violet-black liquid.
  5. Most people can detect ozone in the air because it has a distinct sharp odour that is similar to chlorine bleach.
  6. Ozone exposure causes headaches, burning eyes, and irritation of the respiratory passages.
  7. Modest levels of ozone in the air are extremely damaging to organic materials such as latex, polymers, and animal lung tissue.
  8. Ozone has a weak paramagnetic property.

Chemical Properties of Ozone

  • Ozone acts as a powerful oxidizing agent. Reaction is

O3 ⇢ O2 + O

  • Ozone reduces peroxides to oxides and gets reduced to oxygen

H2O2 + O3 ⇢ H2O + 2O2

Structure of Ozone

Ozone is a bent molecule with symmetry similar to water, according to microwave spectroscopy experiments. The angle formed by O-O-O is 116.78°. One lone pair is sp2 hybridised with the centre atom. The molecule ozone is polar. The molecule can be described as a resonance hybrid with two contributing structures, one with a single bond on one side and the other with a double bond. It has the same isoelectronic properties as the nitrite anion.

Structure of Ozone

Preparation of Ozone

In a laboratory, ozone is created by passing a quiet electric discharge across dry oxygen. Some oxygen molecules dissociate when an electric current is sent through them, and subsequently, atomic oxygen mixes with oxygen molecules to generate ozone.

 O2 ⇢ O + O

O2 + O ⇢ O3

Reactions of Ozone

Ozone is one of the most potent oxidizing agents known, significantly more potent than O2. At large concentrations, it is likewise unstable and degrades into regular oxygen. Its half-life is affected by atmospheric factors like temperature, humidity, and air movement. As the temperature rises, the rate of this reaction accelerates. A spark can cause ozone deflagration, which can occur at ozone concentrations of 10% or more. At the anode of an electrochemical cell, oxygen can also be used to make ozone. Smaller amounts of ozone can be produced by this process for scientific purposes.

With metals: Ozone will oxidize most metals (excluding gold, platinum, and iridium) to oxides of the metals in their highest oxidation state. Consider the following scenario:

Cu + O3 → CuO + O2

Even at ambient temperature, ozone interacts with carbon to produce carbon dioxide:

C + 2O3 → CO2 + 2O2

Ozone Decomposition

Ozone is a harmful gas that is widely found or produced in human surroundings (aircraft cabins, offices with photocopiers, laser printers, and sterilizers, for example), and its catalytic decomposition is critical for pollution reduction. This is the most common kind of breakdown, especially with solid catalysts, and it has a number of advantages, including better conversion at lower temperatures. Furthermore, the product and catalyst can be separated instantly, allowing the catalyst to be recovered without the need for a separation process. Furthermore, noble metals such as Pt, Rh, or Pd, as well as transition metals such as Mn, Co, Cu, Fe, Ni, or Ag, are the most commonly employed materials in the catalytic breakdown of ozone in the gas phase.

In the gas phase, there are two alternative options for ozone decomposition: The first is a thermal decomposition, which decomposes ozone only by the action of heat. The issue is that at temperatures below 250°C, this sort of breakdown is extremely sluggish. However, by working at greater temperatures, the breakdown rate can be increased, albeit at a considerable energy expense. The second is a photochemical breakdown, which occurs when ozone is exposed to ultraviolet radiation (UV), resulting in the formation of oxygen and radical peroxide.

Uses of Ozone

  1. Water treatment plants without filtering systems employ ozone.
  2. Commonly used equipment, such as photocopiers, laser printers, and other electrical devices, can produce ozone.
  3. Ozone therapy is used to disinfect and treat diseases by minimising the impacts of bacteria, viruses, fungi, yeast, and protozoa.
  4. Several ozone-depleting chemicals have features that allow them to efficiently transfer heat from one site to another, making them good refrigerants.

What is an Ozone Layer?

The ozone layer, also known as the ozone shield, is a region of the Earth’s stratosphere that absorbs the majority of ultraviolet radiation from the Sun. It has a high concentration of ozone in comparison to the rest of the atmosphere, although it is relatively low in comparison to other gases in the stratosphere. The ozone layer contains fewer than 10ppm of ozone, whereas the average ozone concentration in the Earth’s atmosphere is around 0.3ppm. The ozone layer is primarily located in the lower stratosphere, between 15 and 35 kilometres above Earth, however, its thickness varies seasonally and geographically.

Sample Questions

Question 1: What is ozone?


Ozone is a gas that exists naturally in our environment. Each ozone molecule has three oxygen atoms and is designated chemically as O3.

Question 2: Where is ozone found in the atmosphere?


Ozone is typically present in two regions of the atmosphere. The troposphere, which stretches from the surface to roughly 10–15 kilometres height, contains around 10% of the Earth’s ozone. The stratosphere, the region of the atmosphere between the top of the troposphere and about 50 kilometres altitude, contains approximately 90 percent of the Earth’s ozone. The “ozone layer” refers to the region of the stratosphere with the highest concentration of ozone. 

Question 3: How is ozone formed?


Ozone is generated in the atmosphere through multistep chemical processes begun by sunlight. The process begins in the stratosphere with an oxygen molecule being torn apart by UV light from the Sun. Ozone is generated in the troposphere through a separate set of chemical reactions that involve both naturally occurring chemicals and those emitted by sources of air pollution.

Question 4: How is ozone measured in the atmosphere?


Instruments on the ground and transported aloft on balloons, aircraft, and satellites measure the amount of ozone in the atmosphere. Some instruments use a continuous air sampler to monitor ozone in a tiny detection chamber. Other technologies use ozone’s distinctive optical absorption or emission qualities to assess ozone across vast distances.

Question 5: What emissions from human activities lead to ozone depletion?


Ozone-depleting substances (ODSs) are released into the atmosphere by some industrial operations and consumer items. The Montreal Protocol regulates the use of produced halogen source gases around the world. These gases transport chlorine and bromine atoms to the stratosphere, where chemical processes destroy ozone. Chlorofluorocarbons (CFCs), which were originally utilised in practically all refrigeration and air conditioning systems, and halons, which were used as fire suppressing agents, are two notable examples.

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