During the reaction of some metals with dilute hydrochloric acid, following observations were made.
i. The temperature of the reaction mixture rises when aluminium (Al) is added.
ii. The reaction of sodium metal is found to be highly explosive.
iii. Some bubbles of a gas are seen when lead (Pb) is reacted with the acid.
Explain these observations giving suitable reasons.
i) When aluminium (Al) and dilute hydrochloric acid react a large amount of heat is produced in the reaction i.e. the reaction is exothermic hence temperature of the reaction mixture rises. (Aluminium replaces the Hydrogen as it is more reactive than hydrogen to form aluminium chloride.)
2Al+6HCl → 2AlCl3 + 3H2
ii) Sodium is a very reactive metal and reacts vigorously with dilute hydrochloric acid to form sodium chloride. This reaction is exothermic (liberation of heat) and is hence highly explosive.
2Na + 2HCl → 2NaCl + H2
where Na is sodium metal, HCl is hydrochloric acid and H2 is hydrogen gas.
iii) When lead (Pb) reacts with hydrochloric acid (HCl), lead displaceshydrogen from hydrochloric acid (since lead is placed above Hydrogen is reactivity series and is hence more reactive that Hydrogen) slowly to form lead chloride (PbCl2) with liberation of hydrogen gas (H2). The bubbles of gas seen is of hydrogen gas.
Pb + 2HCl → PbCl2 + H2