Solutions of Acids, Bases and Salts (Page No - 99) - Chemistry Lakhmir Singh, Class 10 | Extra Documents, Videos & Tests for Class 10 PDF Download

Question 51:
(a) What is bleaching powder ? How is bleaching powder prepared ? Write chemical equation of the reaction
involved in the preparation of bleaching powder.
(b) What happens when bleaching powder reacts with dilute sulphuric acid ? Give equation of the reaction involved.
(c) State two important uses of bleaching powder.
Solution :
(a) Bleaching powder is Calcium oxychloride (CaOCl₂). It is prepared by passing chlorine gas over dry slaked lime.

CaOCl)₂ Cl₂ → Ca0Cl₂ + H₂0 

(b) When bleaching pow&r reacts with dilute sulphuric acid it produces chlorine gas. CaOCl₂ + H₂S0₄ →  CaS0₄ + Cl₂ + H₂0
(c) (i) It is used for disinfecting drinking water supply.
(ii) It is used in the manufacture of chloroform.

Question 52:
(a) What is plaster of Paris ? Write the chemical formula of plaster of Paris.
(b) How is plaster of Paris prepared ? Write chemical equation of the reaction involved.
(c) Explain why plaster of Paris should be stored in a moisture-proof container.
(d) State two important uses of plaster of Paris.
Solution :
(a) Plaster of paris is calcium sulphate hemihydrate. Its chemical formula is: CaSO₄.1/2H₂O.
(b) It is prepared by heating gypsum to a temperature of 100^oC in a kiln; it loses 3/4^th of its water of crystallisation and forms plaster of paris.

(c) This is because the presence of moisture can cause the slow setting of plaster of Paris by bringing about its hydration.
(d) Uses of plaster of Paris:
(i) It is used as a fire proofing material.
(ii) it is used in hospitals for setting fractured bones in the right position to ensure correct healing.

Question 53:
(a) What is a salt ? Give the names and formulae of any two salts. Also name the acids and bases from which these salts may be obtained.
(b) What is meant by ‘a family of salts’ ? Explain with examples.
(c) What is meant by ‘hydrated’ and ‘anhydrous’ salts ? Explain with examples.
(d) Write the names, formulae and colours of any two hydrated salts.
(e) What will be the colour of litmus in an aqueous solution of ammonium chloride salt ?
Solution :
(a) A salt is a compound formed from an acid by the replacement of the hydrogen in the acid by a metal.
Example: Sodium chloride – NaCl; It is obtained from hydrochloric acid and sodium metal.
Ammonium chloride – NH₄Cl; It is obtained from ammonia and hydrochloric acid.
(b) The salts having the same positive ions are said to belong to a family of salts.
Example: Sodium chloride and sodium sulphate belong to the same family of salts called sodium salts.
(c) The salts which contain water of crystallisation are called hydrated salts.
Example: Copper sulphate crystals contain 5 molecules of water of crystallisation.
The salts which have lost their water of crystallisation are called anhydrous salts.
Example: On strong heating, copper sulphate crystals lose all the water of crystallisation and form anhydrous copper sulphate.
(d) Copper sulphate pentahydrate salt – Its chemical formula is CuSO₄.5H₂O. It is blue in colour.
Iron sulphate heptahydrate salt – Its chemical formula is FeSO₄.7H₂O. It is green in colour.
(e) The aqueous solution of ammonium chloride salt turns blue litmus red.