INDUSTRY Chemical formula of Gypsum is CaS04.2H₂O. This mineral is widely deposited throughout the world.


1.  Gypsum is an important source of Ca and S.

2.  In fertilizers, gypsum supplied Ca to the soil for crop production. It is particularly important where soils a subject to extensive leaching.

3.  S is also an important element for plant growth.  

4.  S is an important constituent of protein.

5.  S has some influence on chlorophyll development in plant leaves. It is not part of chlorophyll. But plants with deficiency of S show pale green color.

6.  Boot system of plants is greatly enlarged by the application of S.

       In general, good crops are produced by the application of sulfur-containing materials e.g. gypsum.



When gypsum is heated carefully, it loses 3/4th (3 quarters) of its water of crystallization. The resulting product is called plaster of Paris.

                   2CaSO4. 2H₂O      (CaSO4)2 .H20 + 3H₂O

 However, if gypsum is heated strongly, then an anhydrous product is obtained called dead burnt gypsum.

                   CaSO4. 2H₂O        CaSO4 .H20 + 2H₂O

It absorbs water very slowly.  

The setting of Plaster Of Paris

When plaster of Paris is mixed with half of its weight of water, it forms a plastic-type viscous mass which then sets to a hard porous mass. This process completes in 10 to 15 minutes. During this process, solid mass expands by 1 % by volume and fills the mold. Thus it gives a sharp impression.

Uses of Plaster of Paris  

It is used for

      making plaster walls.

      for casts of sculpture, coins, etc.

      in surgery. Its bandages are used to keep the fractured bone in place after setting.


Special plasters are made by adding certain ingredients.

Cement Plasters

It is plaster of Paris in which glue or other oils have been added. These act as retarders and increase the setting time.

Hard Finish Plasters

It is produced by the calcination of anhydrous sulfate with alum or borax.

These plasters set very slowly but give a hard finish.

When plaster of Paris is mixed with wood pulp and allowed to set in the form of boards, then materials obtained which are used in the construction of buildings as wall boards and partitions.

3. Gypsum is also used as filler in the paper industry.

4. Gypsum is also used in the cement industry.

        Portland cement is obtained by heating a mixture of clay and limestone. The resulting mass called clinker cooled and crushed to a fine powder. During crushing about 2 % gypsum is also added. It prevents the cement from hardening quickly and increases the setting time of cement so that it can be used easily.


Slaked lime Formula of lime is CaO. It is a soft, white compound obtained by the decomposition of  CaCO3.

Slaked Lime

When lime is mixed with water it forms calcium hydroxide called slaked lime. This process is called staking of lime. It is an exothermic process.

                 Cao    +    H₂O           Ca(OH)₂


Cao is used for neutralizing acidic soils.

2. Application of lime to acidic soils increases the amount of readily soluble phosphorous.

3. CaO is used for making lime sulfur sprays which have a solid fungicidal action.

The function of Ca in plant growth

1. Ca is essential for the normal growth of plants. Different plants require different amounts of Ca.

2. Sufficient supply of Ca stimulates the development of root hairs and the entire root system.

3. Ca is also necessary for the normal development of leaves. Sufficient Ca accumulates in leaves and bark.

4. Sufficient supply of Ca is needed for optimum activity of microorganisms that produce nitrates.

5. Presence of Ca in soil controls the availability of phosphorous in the soil.

6. With a deficiency of Ca many substances like Al, Mn, etc accumulate in plants. Their higher concentration is harmful to plants.


1. Large quantities of lime are used in the extraction and refining of metals.

2. Lime is also used in paper industries.

3. It is used in glass making. The lime reacts with sand at high temperatures forming calcium silicate CaSiO3, which is the basis for glass manufacture.

4. Lime is used in the ceramic industry for producing different types of sanitary materials.

5. Ordinary mortar, also called lime mortar, is prepared by mixing freshly slaked lime with sand and water to form a thick paste.

Mortar is made by mixing slaked lime (one volume), sand (three or four books), and water to make a thick paste. This material is hardened or set when placed between stones and bricks. Thus it binds the blocks firmly together.

The reactions to this process are

                 Cao            +      H20              Ca(OH)₂     

                 Ca(OH)₂     +      CO2               CaCO3      +    H20   

                 Ca(OH)₂     +       SIO₂             CaSIO₂     + H₂O

6. Lime is also used in refining sugar and other food products.

7. Lime is used in the manufacturing of bleaching powder, which is used for the bleaching of fabric and paper pulp.

8. Lime is also used in the leather industry.

9. A suspension of calcium hydroxide is called milk of lime and is used as a whitewash.

10. When lime is heated with coke at about 2800°C in an electric furnace, calcium carbide is produced.

                  CaO      +      3C                     CaC2        +        CO

     Calcium carbide on hydrolysis produces acetylene.

                 CaC₂      +       2H₂O     →          Ca(OH)₂   +      C₂H₂

11. Lime is often used as a dehydrating agent. e.g. rectified spirit contains 5 % water which is removed by distilling with lime to produce absolute alcohol. It is also used in the drying of ammonia gas.

12. A mixture of sodium hydroxide and calcium hydroxide (soda lime) is often used to remove both waters a carbon dioxide from certain gases.

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