- Sulphuric acid is a highly corrosive strong mineral acid with the molecular formula H2SO4.
- Sulphuric acid is a diprotic acid.
- Sulphuric acid has a wide range of applications. It is also a central substance in the chemical industry.
Sulphuric Acid is Manufactured in Industry
- Sulphuric acid, H2SO4 is manufactured in industry through Contact Process.
- The raw materials used are sulphur, air and water
- The Contact process consists of four stages.
- Molten sulphur is burnt in dry air to produce sulphur dioxide
- The gas produced is then purified and cooled.
S + O2 → SO2
- Sulphur dioxide can also be produced by burning metal sulphide such as lead(II) sulphide or zinc sulphide in dry air.
2PbS + 3O2 → 2PbO + 2SO2
- In a converter, sulphur dioxide and excess oxygen are passed through vanadium(V) oxide.
- vanadium(V) oxide act as catalyst to expedite the process.
- The optimum condition for maximum amount of product are as follow:
- Temperature: 450 – 500 °C
- Pressure: 2 – 3 atm
- About 99.5% of the sulphur dioxide, SO2 is converted into sulphur trioxide, SO3 through this reversible reaction.
Sulphur trioxide is dissolved in concentrated sulphuric acid to form oleum （H2S2O7）.
SO3 + H2SO4 → H2S2O7
The oleum, H2S2O7 is then diluted with water to produce concentrated sulphuric acid, H2SO4 in large quantities.
H2S2O7 + H2O → 2H2SO4
- The two reactions in the third and fourth stages are equivalent to adding sulphur trioxide, SO3 directly to water.
SO3 + H2O→ H2SO4
- However, this is not done in industry because sulphur trioxide, SO3 reacts too violently with water.
- This produces a lot of heat and a large cloud of sulphuric acid, H2SO4 mist.
- The mist is corrosive, pollutes the air and is difficult to condense.
Environmental and Health Issues of Sulphur Dioxide
Sulphur dioxide, SO2 is one of the by-products of the Contact Process. It is one of the sources of environmental pollution.
- Sulphur dioxide (SO2) is the pollutant primarily associated with acid rain.
- Acid rain occurs when pH of the rain is between 2.4 and 5.0. This is due to the reaction of sulphur dioxide, SO2 with rainwater.
SO2 + H2O→ H2SO3
- The negative effect of acid rains includes
- corrosion of concrete building and metal structure.
- corrosion of monuments and statues made from marble
- causes erosion of top soil.
- killing aquatic life.
- SO2 is an irritant when it is inhaled and at high concentrations may cause severe problems in asthmatics such as narrowing of the airways, known as bronchoconstriction.
- Asthmatics are considerably more sensitive to the effects of SO2 than other individuals.
Sources of SO2
- The principal source of SO2 is from the combustion of fossil fuels in domestic premises and, more importantly, non-nuclear power stations.
- Other industrial processes such as manufacturing of sulphuric acid also contribute to the presence of SO2 in the air.