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Solution


Q.

Read the passage carefully and answer the following questions from (i) to (v):

 

POP or Plaster of Paris is a calcium sulphate hemihydrate. Hemihydrate contains half a molecule of water of crystallisation. It is represented by the formula C a S O subscript 4 times 1 divided by 2 space H subscript 2 O. This structure of half water molecule means that one water molecule is shared by two formula units of C a S O subscript 4.

The name Plaster of Paris was given to this compound because, for the first time, it was made from gypsum which was mainly found in Paris.

 

(iii) Choose the incorrect statement.
1 POP is used to ornate designs on walls and ceilings.  
2 On heating gypsum above 373 K, CaSO4 is obtained.  
3 Dead burnt plaster is CaSO4·2H2O.  
4 The setting of plaster is due to its hydration into gypsum.  

Ans.

(3)