CBSE Class 10 Science 2019 · Paper 31/4/1 · Question 10

Acids, Bases and Salts 3 marks Easy

A white powder is used by doctors to support fractured bones.

(a)Write the name and chemical formula of the powder.
(b)How is this powder prepared ?
(c)When this white powder is mixed with water, a hard solid mass is obtained. Write a balanced chemical equation for the change.
(d)Give one more use of this white powder.

Answer

Plaster of Paris, $CaSO_{4} \cdot \frac{1}{2} H_{2} O$ , is made by heating gypsum at 373 K and sets to gypsum with water.

(a) Plaster of Paris; its chemical formula is

CaSO_{4} \cdot \frac{1}{2} H_{2} O

(calcium sulphate hemihydrate). (b) It is prepared by heating gypsum,

CaSO_{4} \cdot 2 H_{2} O

, at

373

CaSO_{4} \cdot 2 H_{2} O 373 K CaSO_{4} \cdot \frac{1}{2} H_{2} O + 1 \frac{1}{2} H_{2} O

. (c)

CaSO_{4} \cdot \frac{1}{2} H_{2} O + 1 \frac{1}{2} H_{2} O \to CaSO_{4} \cdot 2 H_{2} O

(gypsum, the hard solid mass). (d) It is used for making toys, decorative materials and statues, and for making surfaces smooth (any one).

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