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Ozone – Preparation, Properties, Uses, Effects

Last Updated : 29 Nov, 2021
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Ozone is too reactive to stay in the atmosphere at sea level for long. It is formed from atmospheric oxygen in the presence of sunlight at a height of about 20 kilometres. This ozone layer shields the earth’s surface from an excess of ultraviolet (UV) radiation. It is an unstable, blue, diamagnetic gas with a distinctive pungent odour that shields the earth and its inhabitants from the sun’s intense ultraviolet radiation. Ozone is an allotropic molecular form of oxygen that contains three oxygen atoms (O3). Ozone is produced by passing oxygen through a high voltage potential, which results in the attachment and formation of a third oxygen atom. Soret discovered the molecular formula for ozone (O3) (1863).

Ozone is a type of oxygen that is allotropic. 

Preparation of Ozone 

A silent electrical discharge converts 10% of a steady dry stream of oxygen into ozone. The finished product is called ozonized oxygen. Because the formation of ozone from oxygen is an endothermic process, a silent electrical discharge must be used in its preparation to prevent its decomposition. An ozonizer battery can be used to produce ozone concentrations greater than 10%, and pure ozone can be condensed in a vessel surrounded by liquid oxygen.

3O2 → 2O3 + 142 kJ mol–1

Properties of Ozone

  • Pure ozone exists in three forms: a pale blue gas, a dark blue liquid, and a violet-black solid.
  • Ozone has a distinct odour and is completely safe in low concentrations.
  • If the concentration exceeds about 100 parts per million, breathing becomes difficult, resulting in headaches and nausea.
  • Ozone is thermodynamically unstable in comparison to oxygen because its decomposition results in the release of heat (H is negative) and an increase in entropy (S is positive). These two effects reinforce each other, resulting in a large negative Gibbs energy change (G) for oxygen conversion. As a result, it is not surprising that high concentrations of ozone can be dangerously explosive.
  • It is a powerful oxidizing agent due to the ease with which it liberates atoms of nascent oxygen. Iodine is liberated when ozone reacts with an excess of potassium iodide solution buffered with a borate buffer (pH 9.2), and it can be titrated against a standard solution of sodium thiosulphate. This is a quantitative method for calculating the amount of O3 gas.
  • Experiments have shown that nitrogen oxides (particularly nitric oxide) combine very quickly with ozone, raising the possibility that nitrogen oxides emitted from supersonic jet aircraft exhaust systems are slowly depleting the concentration of the ozone layer in the upper atmosphere.
  • The ozone molecule’s two oxygen-oxygen bond lengths are identical (128 pm), and the molecule is angular as expected, with a bond angle of about 117 degrees.

Uses of Ozone

  1. It’s used as a germicide, disinfectant, and water sterilizer.
  2. It is also used to bleach oils, ivory, flour, starch, and other materials.
  3. In the production of potassium permanganate, it acts as an oxidizing agent.
  4. Ozone is used in water treatment plants that do not have filtration systems.
  5. Commonly used equipment, such as photocopiers, laser printers, and other electrical devices, can also produce ozone.
  6. By minimising the impacts of bacteria, viruses, fungi, yeast, and protozoa, ozone treatment is used in medicine to disinfect and treat disorders.
  7. Several ozone-depleting compounds have refrigerant properties, which means they can efficiently transfer heat from one location to another.

Ozone Layer

The ozone layer is a specific region in the Earth’s stratosphere that acts as a shield against the sun’s incoming ultraviolet rays. The ozone layer absorbs approximately 97-99 % of the sun’s medium-frequency ultraviolet light. 

The ozone layer is made up of three oxygen atoms and is denoted by the symbol O3. There is a lot of ozone in the stratosphere. Surprisingly, ultraviolet radiation itself creates the ozone layer. Ozone is formed when a radiation or electrical discharge causes the oxygen (O2) molecule to split into two distinct atoms, each of which can then join with other atoms to form ozone.

Ozone Layer Depletion

The public became aware of ozone layer depletion following the development of a chemical compound known as chlorofluorocarbons, or CFCs. Because CFCs are light, they can travel through the air and reach the stratosphere. In the presence of ultraviolet radiation, the chlorofluorocarbons react with the ozone layer, causing it to break down into oxygen molecules. 

As a result, the Ozone Layer is depleted. Following the signing of an International Treaty in 1973, the use of CFCs was reduced and then banned. In the 1980s, it was discovered that the ozone layer in an area of the Antarctic stratosphere had dropped to levels as low as 33% of pre-1975 levels. The Ozone hole was named after this area.  

The chemical chlorofluorocarbons, or CFCs, are one of the major causes of ozone layer depletion. CFCs are made up of carbon, fluorine, and chlorine. They are extremely durable and can withstand harsh conditions. CFCs do not react in general, but only with sunlight when they degrade and release chlorine. 

Effects of ozone layer depletion

  1. More UV rays enter the atmosphere as the ozone layer depletes. When these UV rays come into contact with human skin, they have the potential to cause malignant skin cancer. Cataracts can also be caused by it. Vitamin D is synthesized in our bodies when it reacts with UV rays. Excess vitamin D can also cause an increase in blood calcium levels, which can lead to an increase in mortality rates.
  2. The thinning of the ozone layer has resulted in epidermal damage in whales as a result of high UV rays. Because of ozone layer depletion, more sun damage has been observed in many aquatic animals.
  3. Increased UV rays can harm plant life by damaging it when exposed to high levels of UV rays. Plant growth will also be hampered.

Sample Questions 

Question 1: Is ozone toxic when inhaled?


Ozone, whether in its pure form or in combination with other chemicals, can be hazardous to one’s health. When inhaled, ozone can cause lung damage. Low ozone levels can cause throat pain, coughing, shortness of breath, and pulmonary inflammation.

Question 2: How many lone pairs are in Ozone?


The oxygen containing double bond has two lone pairs in ozone, the oxygen containing positive charge has one lone pair, and the oxygen containing negative charge has three lone pairs. So there are a total of six lone pairs in one ozone molecule.

Question 3: Why is ozone bent instead of linear?


Electrons will repel the electron cloud of the two oxygen atoms on each end, according to the VSEPR (valance shell electron pair repulsion) theory. The end O groups will be pushed down as a result, giving the O3 molecule a bent molecular geometry or V shape.

Question 4: How is the ozone layer getting depleted?


The chemical chlorofluorocarbons, or CFCs, are one of the major causes of ozone layer depletion. CFCs are made up of carbon, fluorine, and chlorine. They are extremely durable and can withstand harsh conditions. CFCs do not react in general, but only with sunlight when they degrade and release chlorine.

Question 5: What is the effect of ozone layer depletion on humans?


More UV rays reach the atmosphere as the ozone layer depletes. These UV rays can develop malignant skin malignancies when they come into touch with human skin. Cataracts can potentially be a result of it. Vitamin D is produced in our bodies when UV rays react with it. Excess vitamin D can boost calcium levels in the blood, which can raise mortality rates.

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