question_answer

  During the reaction of some metals with dilute hydrochloric acid, following observations were made (a) Silver metal does not show any change. (b) The temperature of the reaction mixture rises when aluminium (Al) is added. (c) The reaction of sodium metals is found to be highly explosive. (d) Some bubbles of a gas are seen when lead (Pb) is reacted with the acid. (e) A gas is produced when sodium carbonate is added to the acid. Explain these observations giving suitable reasons. Or Write chemical equations representing each of (a) combination reaction. (b) thermal decomposition reaction. (c) double displacement reaction. (d) neutralization reaction. e) redox reaction.

Answer:

  (a) Silver is a very less reactive metal. Thus, it does not react with dilute HCl.                                                       (1) (b) The reaction of Al with dilute HCl is exothermic i.e., heat is produced in the reaction, hence the temperature of the reaction mixture rises.                                                                                                                           (1) (c) Sodium is a very reactive metal. It reacts vigorously with the evolution of heat too.                                                   (1) (d) Bubbles are seen due to the evolution of O2 gas.                                                                                                                                       (1) (e) gas is produced whenreacts with dilute HCl.                                                                                                                                                                           (1) Or (a) Combination reaction (when two or more reactants combine to form single product)                                                                                                                                       (1) (b) Thermal decomposition reaction (when a reactant decomposes into two or more substances by heating)                                                                                                                             (1) (c) Double displacement reaction (when two compounds exchange their ions to form two new compounds)                                                                                                        (1) (d) Neutralization reaction (when an acid reacts with a base to form salt and water.)                                                                                                                                         (1) (e) Redox reaction (when oxidation and reduction take place simultaneously)                                                                                                (1)