+91-8076753736 support@wiredfaculty.com
logo
logo

Sponsor Area

The S-Block Elements

Question
CBSEENCH11007165
Wired Faculty App

What is Plaster of Paris? How is it prepared? What are its properties and uses?

Solution

Plaster of Paris is calcium sulphate hemihydrate.
CaSO subscript 4. space 1 half straight H subscript 2 straight O space or space left parenthesis CaSO subscript 4 right parenthesis subscript 2. space straight H subscript 2 straight O
Preparation:
(i) From gypsum (CaSO4. 2H2O): When gypsum is heated to about 393 - 403 K, partial dehydration takes place with the formation of Plaster of Paris. 
2 CaSO subscript 4. space 2 straight H subscript 2 straight O space rightwards arrow from 393 minus 403 space straight K to Heat of space stack 2 CaSO subscript 4. space straight H subscript 2 straight O with Plaster space of space Paris below space plus space 3 straight H subscript 2 straight O
(ii) On a large scale, gypsum is gradually heated in a large steel vessel, holding several tonnes of material. This steel vessel is provided with a mechanical stirrer. During heating, the gypsum is stirred mechanically and the temperature is maintained between 393 - 403 K.
2 CaSO subscript 4. space 2 straight H subscript 2 straight O space space space rightwards arrow from 393 minus space 403 straight K to Heat of space stack left parenthesis CaSO subscript 4 right parenthesis subscript 2 space. with Plaster space of space Paris below space straight H subscript 2 straight O space plus space 3 straight H subscript 2 straight O
The temperature should be controlled carefully between 393 - 403 K, otherwise above this temperature (say 473 K), the whole of the water of hydration is lost and the gypsum gets dead burnt.

Properties:
(i) It is a white powder.
(ii) When mixed with water, Plaster of Paris quickly solidifies to gypsum with the evolution of heat and also expands slightly.
stack 2 CaSO subscript 4. space 1 half straight H subscript 2 straight O with Plaster space of space Paris below space plus space 3 straight H subscript 2 straight O space space rightwards arrow space space space stack 2 CaSO subscript 4. space 2 straight H subscript 2 straight O with Gypsum below
(iii) The action of heat: When plaster of Paris is heated at 473 K, it forms anhydrous calcium sulphate. 
Uses. (i) It is used in surgery for plastering fractured parts of the body.
         (ii) It is used for making casts for statues and for preparing blackboard chalks. 

Some More Questions From The s-Block Elements Chapter

Why caesium can be used in photoelectric cell while lithium can not be?

In aqueous solution, Li+ ion has lowest mobility. Why?

Lithium has highest ionisation energy in group 1 elements, yet it is strongest reducing agent. Comment.

The softness of group 1 elements increases down the group with increasing atomic number. Give reason. 

Which is the most reactive alkali metal and why?

Why alkali metals do not form M2+ ions?

Name the radio active element in group 1. How does it resemble with the remaining elements of the group?

Why alkali metals are normally kept in kerosene oil?

Why lithium cannot be stored in kerosene?

Why does lithium form complexes?

Mock Test Series

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation