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Tinashe Chikoko and Samson Mujakwi
Industrial processes is an Ordinary Level integrated science topic which lies under the section called Science in Industry. O-Level inter science comprises of five sections namely Science in Agriculture, Science in Energy uses, Science in Mechanical Systems and Structures, Science in the Community and Science in Industry.

Students find industrial science challenging as compared to other sections mainly because the content is encountered later in life whereas the concepts of other sections are first introduced at primary level.

If a student wants to be good at industrial science he or she must develop interest in the concepts and regular practice is a prerequisite. In this article we are going to enlighten students on the concepts of the manufacture of sulphuric acid and also to give hints and tips on the examination areas of these concepts so that students will not be lost when it comes to examinations. The ZIMSEC syllabus requires students to know the following concepts at the end of the topic.

Sulphuric acid
– Outline the manufacture of sulphuric acid;
– State the optimum conditions for the manufacture of sulphuric acid;
– State the industrial uses of sulphuric acid;

Contact
Process; sources of raw materials
Temperature and catalyst.

Drying agent: production of fertiliser, paint, plastics, and detergents and in paper making.

Sulphuric acid in Zimbabwe is manufactured at Zimphos by a process called the contact process as outlined below. The two raw materials for this process are sulphur and iron pyrites.

Contact process
In the first step, sulphur is roasted in air to produce sulphur dioxide according to the following equation
Sulphur +oxygen sulphur dioxide

This is then oxidised to sulphur trioxide using oxygen in the presence of a vanadium (V) oxide catalyst. This reaction is reversible and the formation of the sulphur trioxide is exothermic meaning it produces a lot of heat to the surroundings according to the following equation.

Sulphur dioxide + oxygen Sulphur trioxide

The temperature appropriate for this reaction is about 450 to 500 degrees celsius and a pressure of about 1 atm.

Sulphur trioxide being a non metal oxide implies that dissolving it in water will produce sulphuric acid but in industry it is not like so because the heat of reaction will be very high such that it produces a mist of sulphuric acid which is difficult to condense.

Uses of sulphuric acid
The manufacture of fertilisers

The major use of sulphuric acid is in the production of phosphoric acid which is used to make phosphate fertilisers. These are added to the soil to improve plant growth. In ancient times farmers used natural fertilisers such as nitrogen-fixing plants like clover to improve their crop yield but today modern synthetic fertilisers are widely used. Their use, however, is hotly debated with critics arguing that organically-produced foodstuffs are better for people, wildlife and the environment.

Metal processing
‘Pickling’ is a term used to describe the treatment of metals to remove impurities, rust or scale from the surface, such as in steel making. Today, the use of sulphuric acid for this purpose has decreased a little as the industry now favours the use of hydrochloric acid. Although hydrochloric acid is more expensive than sulphuric acid, it produces results more quickly and minimises the loss of base metals during the pickling process.

The manufacture of lead-acid type batteries
Sealed-unit lead-acid type batteries are used in the automotive industry for cars and trucks. This type of battery was invented in 1859 by Frenchman Gaston Plante and the basic design has changed remarkably little over the past 100 years ago. Sulphuric acid is used in a dilute form to act as an electrolyte to allow the flow of electrons between the plates in the battery. Sulphuric acid used in this way is commonly called battery Acid. It can vary in strength according to the battery manufacturer but is generally between 28 to 32 percent or between 4.2 to 5 molar.

Possible examination questions
1) Outline the industrial manufacture of sulphuric acid (6)
2) State any three uses of sulphuric acid (3)
3) The production of sulphur trioxide from sulphur dioxide is reversible and exothermic. Explain what is meant by reversible and exothermic (3)
4) Explain why sulphur trioxide is not mixed directly with water (3)

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