Question

(a) What is double displacement reaction? Explain with an example.

(b) A small amount of quick lime is added to water in a beaker.

     (i) Name and define the type of reaction that has taken place.

    (ii) Write balanced chemical equation for the above reaction and the chemical name of the product formed.

    (iii) List two main observations of this reaction. 

Answer 1

(a) Double Displacement Reaction : Reactions in which there is an exchange of ions between the reactants are called Double Displacement Reactions. 

Example : \[\ce{Pb(NO3)2_{(aq)} + 2KI_{(aq)} -> \underset {\text{(Yellow ppt)}}{PbI_2}( v) + 2KNO3_{(aq)} }\]

(b) (i)  Reaction taking place is combination reaction. A reaction in which two or more reactants combine to form a single product is known as combination reaction. 

 \[\ce{\underset{\text{Quick lime}}{CaO_{(s)}} + H2O_{(l)} -> \underset{\text{(Calcium hydroxide)}}{Ca(OH)2_{(aq)}} + Heat}\]

(iii) Two main observations :Calcium oxide when reacts vigorously with water produces slaked lime i.e Ca(OH)₂ . A large amount of heat is evolved . This is an Exothermic reaction .