What is the chemical name and chemical formula of plaster of paris ?

Question

(a) What is the chemical name and chemical formula of plaster of paris ?
(b) Write a reaction between Plaster of Paris and water. 
(c) Write two uses of washing soda. 

(d) What is chlor-alkali process ? Name two products obtained during this process.

Answer 1

(a) Chemical name of Plaster of Paris is Calcium sulphate hemihydrate. 
Chemical formula of Plaster of paris = CaSO₄. 1/2 H₂O. 

(b) When it is mixed with water, crystals of gypsum are produced and set into hard mass. 

CaSO₄. 1/2H₂O + 3/2 H₂O →  CaSO₄.2H₂O 

 Plaster of Paris                         Gypsum 

(c) Uses of Washing Soda : 

(i) It is used in softening of hard water. 

(ii) It is used as cleaning agent for domestic purposes.

 (d) Caustic Soda (NaOH) is obtained by the electrolysis of aqueous solution of sodium chloride (called brine) and the process is called chlor-alkali. Products obtained during this process are chlorine and hydrogen.