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       The chemical formula of sulphuric acid is H2SO4. It is a very important industrial chemical. It is also called king of chemicals because a large number of substances are manufactured from it.

Manufacture of Sulphuric Acid

       Sulphuric acid is manufactured by Contact process. This process involves following four steps:

1. Formation of Sulphur Dioxide

       In first step sulphur is burnt in air to produce sulphur dioxide gas.

                   S     +     O2         SO2
               Sulphur   Oxygen                      Sulphur dioxide

2. Formation of Sulphur Trioxide

       Sulphur dioxide is then mixed with more air and heated to 450°C by passing over vanadium oxide catalyst, to form sulphur trioxide.

            2SO2     +     O2         2SO3     +     Heat
     Sulphur dioxide   Oxygen               Sulphur trioxide

3. Formation of Oleum

       Sulphur trioxide is then dissolved in concentrated sulphuric acid to form a thick liquid called oleum (H2S2O7).
               H2SO4       +       SO3         H2S2O7
         Sulphuric acid    Sulphur trioxide                         Oleum

4. Formation of Sulphuric Acid

       Oleum is then diluted with water to get sulphric acid.

               H2S2O7       +       H2O        H2SO4
               Oleum                 Water                         Sulphuric acid

Physical Properties of Sulphuric Acid

       Sulphuric acid is used in the form of concentrated sulphuric acid and dilute sulphuric acid. So, we will study their physical and chemical properties separately.

1. Concentrated Sulphuric Acid

       It is a colourless oily liquid which contains about 98% sulphuric acid and 2% water.

Chemical Properties of Concentrated Sulphuric Acid

1) As a Dehydrating Agent

       Concentrated sulphuric acid can dehydrate i.e. can remove water from many substances such as sugar, paper, wood, copper sulphate etc.

2) Dehydration of Sugar

       When concentrated sulphuric acid is added in sugar, it removes 11 molecules of water from sugar molecule and converts it into a black mass of carbon called sugar charcoal.

               C12H22O11           12C      +      11H2O
                  Sugar                                      Carbon            Water

Dehydration of Copper Sulphate Crystals

       Copper sulphate is a blue coloured compound containing 5 molecules of water of crystallization. Its molecular formula is CuSO4.5H2O. When concentrated sulphuric acid is added in blue crystals of hydrated copper sulphate, it removes 5 molecules of water of crystallization from crystals of copper sulphate to form anhydrous copper sulphate which is white in colour.

            CuSO4.5H2O           CuSO4      +      5H2O
         Copper sulphate                        Copper sulphate       Water
          (Blue crystals)                           (White powder)

As an Oxidising Agent

       Concentrated sulphuric acid acts as an oxidising agent and oxidises carbon and sulphur to carbon dioxide and sulphur dioxide respectively.

  C    +    2H2SO4      2H2O   +     2SO2     +      CO2

Carbon    Sulphuric acid                                Water     Sulphur dioxide   Carbon dioxide

            S    +    2H2SO4      2H2O   +     2SO2

          Sulphur    Sulphuric acid                                 Water       Sulphur dioxide

2. Dilute Sulphuric Acid

       It contains about 10% sulphuric acid and 90% water. It is always obtained by diluting concentrated sulphuric acid with water. It should be noted that while preparing dilute sulphuric acid concentrated sulphuric acid is added into water. Water should never be added into concentrated sulphuric acid. This is because when water is added to acid a large amount of heat is produced which can throw out the drops of acid and can burn you. However, if acid is added to water, the heat evolved is absorbed by large amount of water.

Chemical Properties of Dilute Sulphuric Acid

1) Reaction with Metals

       Dilute sulphuric acid reacts with reactive metals such as zinc and iron to form hydrogen gas and metal sulphates.

            Zn    +    H2SO4      ZnSO4     +      H2
           Zinc    Sulphuric Acid                   Zinc sulphate   Hydrogen

            Fe    +    H2SO4      FeSO4     +      H2
           Iron    Sulphuric Acid                   Iron sulphate   Hydrogen

Reaction with Carbonates

       Dilute sulphuric acid reacts with metal carbonates to liberate carbon dioxide.

    Na2CO3    +     H2SO4      Na2SO4   +     CO2    +     H20

Sodium carbonate    Sulphuric acid                    Sodium sulphate    Carbon dioxide    Water

Reaction with Alkalis

       Dilute sulphuric acid reacts with alkalis such as sodium hydroxide to form normal salts called sulphates and acid salts called hydrogensulphates.

      2NaOH       +         H2SO4      Na2SO4     +      2H2O
Sodium hydroxide    Sulphuric Acid                 Sodium sulphate     Water
                                                                        (Normal salt)

        NaOH       +         H2SO4      NaHSO4     +      2H2O
Sodium hydroxide    Sulphuric Acid      Sodium hydrogensulphate   Water
                                                                        (Acid salt)

Uses of Sulphuric Acid

  1. It is used in the manufacture of fertilizers.
  2. It is used as a reagent in laboratories.
  3. It is used for manufacturing paints, pigments and dyes.
  4. It is used for manufacturing soaps and detergents.
  5. It is used for manufacturing plastics and synthetic fibres.
  6. It is used as a dehydrating agent.