Oxoacids of Sulphur: An Overview and Explanation

Before we understand what oxoacids of sulfur are and what are the different types of oxoacids of sulphur , it is important to take a second to remember what sulphur is. Sulphur is a rotten egg-smelling nonmetal that is tasteless and colorless. Sulphur occurs as sulfide and sulfate minerals or it occurs in its pure form. The applications of sulphur include batteries, detergents, fungicides, fireworks, and so on. And now that you know all about sulphur, let us understand the oxoacids of sulphur.

Oxoacids are essentially those acids that contain oxygen. Oxoacids are Acids containing hydrogen, oxygen, and another element. Oxoacids of sulfur can be found in either one of the four states- free, salt, free along with salt and solution state. Oxoacids of sulfur contain at least one S=O Bond and one S-OH or S-SH bond. Sulfur shows a tetrahedral structure to oxygen.. Some of these acids are unstable and cannot be isolated. They normally exist in aqueous solution or in the form of their salts. Structures of some important oxoacids are shown below.

Key Terms: Sulphuric acid, Oleum, Oxoacids, Sulphide ores, Hydrogen, Oxygen, Salt

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Sulphuric acid (H₂SO₄)

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Manufacturing process of sulphuric acid (Contact process)

Sulphuric acid is manufactured by the contact process. It is a 3 step process:

1. Oxidation of sulphur or sulphide ores by burning to produce SO₂
2. Transforming SO₂ into SO₃ by catalytic oxidation (using catalysts such as V₂O⁵)
3. Absorbing SO₃ in H₂SO₄ to give oleum.(H₂S₂O₇)

Acid obtained from the contact process is 96-98% pure. The most important step of the contact process is the second step. Its details are given below:

Step’s of the contact process

This reaction is a reversible reaction. Since the volume reduces in the forward direction, high pressure and low temperature is maintained to have an optimum yield. In the plants, a temperature of 720 K and pressure of 2 bar is maintained for operation. The process flow diagram is shown below.

Oleum obtained from this process as an end result is diluted to get sulphuric acid of the desired concentration. In the industry, oleum production and dilution to make sulphur is done in one step to save money.

  Oleum

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Properties of Sulphuric acid

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• Sulphuric acid is soluble in water. When it is dissolved, a huge amount of heat is liberated. It is a dangerous reaction. Hence, the concentrated acid is added very slowly to water while stirring it constantly.
• Ionising of H₂SO₄ in an aqueous solution happens in 2 steps:

Properties of Sulphuric acid

Owing to its high k_a1 value, it is a very strong acid.

• Concentrated sulphuric acid is a strong dehydrating agent. That is why it is used in industry for drying of gases which do not react with it. It also dehydrates organic compounds. The most common example of that is charring of carbohydrates. 
• It is a moderately strong oxidising agent in its hot concentrated form. Its oxidising power is intermediate between phosphoric and nitric acids. Both metals and nonmetals are oxidised by concentrated sulphuric acid, which is reduced to SO₂

_​Also Read: Magnetic properties transition elements