Sulphuric Acid

  1. Sulphuric acid is a highly corrosive strong mineral acid with the molecular formula H2SO4.
  2. Sulphuric acid is a diprotic acid.
  3. Sulphuric acid has a wide range of applications. It is also a central substance in the chemical industry.

Uses of Sulphuric Acid

  1. Applications of sulphuric acid include
    1. manufacturing fertiliser
    2. manufacturing detergent
    3. manufacturing pesticide
    4. manufacturing synthetic fibre
    5. as electrolyte in lead-acid accumulator
    6. removing metal oxide
    7. manufacturing paint
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Contact Process

Sulphuric Acid is Manufactured in Industry

  1. Sulphuric acid, H2SO4 is manufactured in industry through Contact Process.
  2. The raw materials used are sulphur, air and water
  3. The Contact process consists of four stages.

    Stage 1

    1. Molten sulphur is burnt in dry air to produce sulphur dioxide
    2. The gas produced is then purified and cooled.
      S + O2 → SO2
    3. 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

    Stage 2

    1. In a converter, sulphur dioxide and excess oxygen are passed through vanadium(V) oxide.
    2. vanadium(V) oxide act as catalyst to expedite the process.
    3. The optimum condition for maximum amount of product are as follow:
      1. Temperature: 450 – 500 °C
      2. Pressure: 2 – 3 atm
    4. About 99.5% of the sulphur dioxide, SO2 is converted into sulphur trioxide, SO3 through this reversible reaction.

    Stage 3

    Sulphur trioxide is dissolved in concentrated sulphuric acid to form oleum (H2S2O7).
    SO3 + H2SO4 → H2S2O7

    Stage 4

    The oleum, H2S2O7 is then diluted with water to produce concentrated sulphuric acid, H2SO4 in large quantities.
    H2S2O7 + H2O → 2H2SO4

    Note:

    1. The two reactions in the third and fourth stages are equivalent to adding sulphur trioxide, SO3 directly to water.
      SO3 + H2O→ H2SO4
    2. However, this is not done in industry because sulphur trioxide, SO3 reacts too violently with water.
    3. This produces a lot of heat and a large cloud of sulphuric acid, H2SO4 mist.
    4. The mist is corrosive, pollutes the air and is difficult to condense.
    Summary

    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.

    Acid Rain

    1. Sulphur dioxide (SO2) is the pollutant primarily associated with acid rain.
    2. 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
    3. The negative effect of acid rains includes
      1. corrosion of concrete building and metal structure.
      2. corrosion of monuments and statues made from marble
      3. causes erosion of top soil.
      4. killing aquatic life.

    Health Effects

    1. 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.
    2. Asthmatics are considerably more sensitive to the effects of SO2 than other individuals.

    Sources of SO2

    1. The principal source of SO2 is from the combustion of fossil fuels in domestic premises and, more importantly, non-nuclear power stations.
    2. Other industrial processes such as manufacturing of sulphuric acid also contribute to the presence of SO2 in the air.

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