Sulphur Dioxide

Introduction

Sulphur dioxide is practically a very dull gas however, it releases a very strong and pungent odour. This is highly toxic to breathe. This gas has several definitive characteristic traits, like, as this can naturally occur in a colourless form and can readily mix into water. This gas can be prepared in laboratories as well.

What is sulphur dioxide?

Sulphur dioxide is also acknowledged as sulphurous anhydrate or sulphur (IV) oxide. This chemical compound has been utilised by humans for various usages across history. In the early days, Romans used this gas in the preparation of wine. This is a colourless gas and it is heavier than air. It is known to be highly toxic for humans and can irritate the mucous membrane and the eyes. This gas is used to prepare other chemicals and is industrially utilised to process food. This gas releases a foul odour and it can easily mix with water.

This gas contains sp2 hybridised structure. The O-S-O bond angle is 119° and a (σ) sigma and pi (π) bridge connect each of the oxygen atoms in the sulphur dioxide molecule. The sp2-p bond overlaps and forms an σ sigma bond between sulphur and oxygen atoms whereas one of the π links is formed by pπ-pπ overlap. The electronic configuration of S is $\mathrm{1s^{2}2s^{2}2p^{6}3s^{2}3p^{4}}$. An electron from the 3p orbital relocates to the 3d orbital in the course of synthesis of sulphur dioxide

Sulphur dioxide: Occurrence

Figure 1 − Sulphur dioxide

This gas exists in small concentrations in the earth’s atmosphere. However, this gas is found in abundance on other planets of the solar system. For example, on Venus, this gas is found in a significant amount. This gas is also found abundantly on Mars. Io, a natural satellite of Jupiter is composed of about 90% of sulphur dioxide. It also exists in frozen form in Galilean moons and is found in the mantle of Ganymede, Europa and Callisto

On Earth, this gas is naturally liberated from a volcanic eruption. It is one a primary source of air pollution and global warming. This gas is also released into the air as a by- product of various industrial activities. It releases into the air from burning coal and oil at various power plants. It releases into the air from copper smelting processes.

Sulphur dioxide: Preparation

Various industrial processes some of the essential ways are mentioned below can also prepare this gas −

• In the laboratory, sulphur dioxide is prepared by mixing metallic sulphite or bisulphite with dilute acid. The most common example is that it can be prepared by mixing sodium sulphite with dilute sulphuric acid and it liberates sulphur dioxide as a by-product along with water.

• Various industrial processes prepare this gas as well, it is obtained as a by- product and it is released by roasting sulphide ores. The gas that is obtained from this process is first dried out, then it is liquefied under a high amount of pressure and then stored in steel cylinders to be used for different commercial purposes.

• It is obtained by burning sulphur in presence of oxygen.

• Heating of sulphur, copper and silver in sulphur acid solution also gives out sulphur dioxide gas.

Properties of sulphur dioxide

The key properties of Sulphur dioxide are mentioned below −

Physical properties

• It is a colourless gas and is also poisonous. It generates a foul odour.

• This gas can easily mix with water. At 0°C, a volume of water is capable of dissolving around 8 litres of this gas.

• This gas can be liquified under a high amount of pressure at room temperature.

• Sulphur dioxide can act as both a reducing and an oxidising agent.

• This gas is not combustible.

Chemical properties

• Sulphur dioxide can readily mix with water and liberate sulphurous acid. The acidic solution of this substance forms a crimson shade on blue litmus paper. Hence the gas is considered an anhydrate.

• Sulphur dioxide can swiftly mix with sodium hydroxide solution to generate sodium sulphite which in turn reacts with the extra sulphur dioxide to create sodium hydrogen sulphite.

• Sulphur dioxide when heated through lime water turns the solution milky.

• Sulphur dioxide mixes with oxygen to create sulphur trioxide.

• In presence of moisture, it acts as a bleaching agent.

Uses of sulphur dioxide

Some of the uses of this substance are mentioned below −

Figure 2 − Uses of Sulphur dioxide

• It acts as a food preservative in food industries.

• Sulphur dioxide functions as a bleaching agent and helps in the removal of excess chlorine.

• This substance acts as a refrigerant in cold storage plants.

• This gas functions as a reagent and solvent in laboratories.

Conclusion

Sulphur dioxide is a widely used gas for various industrial processes. This gas is known to be toxic in nature and it generates a strongly pungent odour. This gas can be obtained through the fumes liberated through volcanic eruptions or can be prepared by various chemical processes. Precautions should be undertaken while handling this substance as it has harmful effects on human organs.

FAQs

1. What are the harmful effects of sulphur dioxide?

Sulphur dioxide can create various respiratory disorders. It mainly causes bronchitis under prolonged exposure. This gas is known to irritate the throat, nose and lungs. Inhalation of this gas will lead to coughing and wheezing and give rise to asthmatic conditions.

2. How can sulphur dioxide create acid rain?

Acid rain happens when it is released into the atmosphere by sulphur dioxide and nitrogen oxides and then it is carried by wind currents. The gas combines with nitrogen oxides to create sulphuric and nitric acid with water and oxygen which then precipitates on earth.

3. How is sulphur dioxide formed?

This gas is obtained by burning coal or oil and smelting the mineral ores that contains sulphur for example, zinc, iron and lead ores. It is a colourless gas that has a strong odour.