question_answer 59)

  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 metal is found to be highly explosive (d) Some bubbles of a gas are seen when lead(Pb) is reacted with the acid Explain these observations giving suitable reasons.

Answer:

  (a) This is because silver is below hydrogen in the reactivity series so, cannot displace hydrogen when reacted with acid. (b) The reaction of Al with dilute HCI is exothermic i.e., heat is produced in the reaction, hence the temperature of the reaction mixture rises. (c) Sodium is a very reactive metal. It reacts explosively (extremely rapidly) with hydrochloric acid to form sodium chloride and hydrogen with the evolution of heat too. H2 gas produced catches fire immediately (d) Lead is present just above the hydrogen in the activity series of metals. Hence, it is slightly more reactive and displace hydrogen from acid very slowly and to a small extent. Therefore, only bubbles ofH2 are seen to evolve.