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
NaOH + H2SO4 NaHSO4 + 2H2O
Sodium hydroxide Sulphuric Acid Sodium hydrogensulphate Water
Uses of Sulphuric Acid
- It is used in the manufacture of fertilizers.
- It is used as a reagent in laboratories.
- It is used for manufacturing paints, pigments and dyes.
- It is used for manufacturing soaps and detergents.
- It is used for manufacturing plastics and synthetic fibres.
- It is used as a dehydrating agent.
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