Q: What is plaster of Paris? How is it prepared?
Ans: Calcium sulphate hemi hydrated is commonly known as "plaster of Paris". Chemical formula: CaSO4.1/2H2O
Plaster of Paris is prepared by gypsum.
Preparation
 
When gypsum is heated up to 1000C ,it loses some molecules of water of crystallization and forms an amorphous white solid known as plaster of Paris.
CaSO4.2H2O è CaSO4.1/2H2O+ 3/2H2O
Properties
 
Plaster of Paris when mixed with water sets within few minutes. The setting of plaster of Paris takes place with expansion and its surface becomes very smooth .Due to this property plaster of Paris is used in moulds.
Question: What is Epsom salt?
How is it prepared.
 
Magnesium sulphate hepta hydrated is commonly known as "Epsom salt".
Chemical formula: MgSO4.7H2O
Properties & uses
 
It is a semi transparent white crystalline solid.
It is soluble in water.
It is used as purgative in medicines.
It is used in Paper, soap and ceramics industry .
Methods of preparation
 
Epsom can be prepared by treating suitable substance with Sulphuric acid
From Mg:
Mg + H2SO4 è MgSO4 + H2
From MgCO3 :
MgCO3 when treated with H2SO4. MgSO4 is obtained.
MgCO3 + H2SO4 è MgSO4 + H2O + CO2
From Mg(OH)2:
Mg(OH)2 + H2SO4 è MgSO4 + 2H2O
From MgO :
MgO + H2SO4 è MgSO4 + H2O
Effect of Heat
 
When Epsom is heated, it loses water of crystallization to form anhydrous magnesium sulphate.
MgSO4.7H2O è MgSO4 + 7H2O
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