Sulphur (GCSE Chemistry)

Sulphur

Sulphur

Sources of Sulphur

• Sulphur is mainly found underground. Sulphur can be found as an element in the ground, usually in volcanic areas.
• Petroleum and natural gas release sulphur. Sulphur is released from petroleum and natural gas as a by-product.
• Sulphide ores contain sulfur. Some metal ores such as copper pyrites contain sulphur.

Uses of Sulphur

• Sulphur is used to in the manufacture of sulphuric acid. Sulphuric acid is produced by the Contact process. We will cover this in more detail later on.
• Sulphur is used to make paper. Sulphur compounds are used to break down wood into pulp, to then make paper.
• Sulphur is used as a food preservative. Sulphur can kill bacteria therefore is good in preserving food.

The Contact Process

During the Contact Process, sulphuric acid is manufactured using sulphur and oxygen from the air. It can be split up into three stages as seen below.

Steps of the Contact Process

1.Sulphur is oxidised. Oxygen reacts with sulphur to form sulphur dioxide.

S + O₂ → SO₂

2. Sulphur dioxide is oxidised to form sulphur trioxide. A V₂O₅ catalyst is used alongside specific conditions which are covered further on.

2SO₂ + O₂ ⇌2SO₃

3. Oleum is formed. Sulphur trioxide reacts with sulphuric acid to form H₂S₂O₇. This is a thick liquid known as oleum. Oleum is then reacted with water, forming concentrated sulphuric acid.

SO₃ + H₂SO₄ → H₂S₂O₇

H₂S₂O₇ + H₂O → 2H₂SO₄

Conditions for the Oxidation of Sulphur Dioxide

• A lower temperature yields a higher equilibrium. The oxidation of sulphur dioxide is an exothermic reaction, therefore a lower temperature favours the forward reaction. However, temperatures too low are not efficient, therefore a compromise is made at around 450 degrees for the optimal temperature.
• A higher pressure yields a higher equilibrium. As the pressure increases, the position of equilibrium shifts to the right as there are fewer gas molecules. However, a high temperature is very expensive and can cause problems with corrosive mixtures of gases. Therefore a compromise is made at 2 atm for the optimal pressure.

Sulphuric Acid

Properties of Sulphuric Acid

• Sulphuric acid is a dibasic acid. A dibasic acid is an acid where two hydrogen atoms can be donated and then replaced with a metal, as seen in sulphuric acid.
• Concentrated sulphuric acid is a powerful oxidising agent and dehydrating agent. It is corrosive and is used to remove water from compounds.

Uses of Sulphuric Acid

• Dilute sulphuric acid is used as a catalyst and for cleaning. In some organic reactions, sulphuric acid acts as a catalyst. It is also used in cleaning metal surfaces
• Concentrated sulphuric acid has many uses. Some of its main uses include in phosphate fertilisers, soaps and batteries. Also in the production of paints and dyes.