Question 31
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.

(a) This is because silver is less reactive in nature and cannot displace hydrogen from dilute hydrochloric acid, hence it lies below it in the activity series of metals.

$Ag\left(s\right)+HCl\left(dil\right)⟶Noreaction$
(b) The reaction of aluminum with dilute hydrochloric acid is exothermic, i.e., heat is released. Hence, the temperature of the reaction mixture rises.

$2Al\left(s\right)+6HCl\left(dil\right)⟶2AlC{l}_3\left(l\right)+3H_2\left(g\right)+heat$
(c) Sodium metal is a highly reactive element, its reaction with dilute hydrochloric acid is extremely vigorous and exothermic.

$2Na\left(s\right)+2HCl\left(dil\right)⟶2NaCl\left(s\right)+H_2\left(g\right)+heat$
(d) When lead is treated with hydrochloric acid, it displaces hydrogen, and bubbles of hydrogen gas are evolved. The reaction occurs as follows:
$\text{Pb(s)}+2\text{HCl}\text{(aq)}\to {\text{PbCl}}_2\text{(s)}+{\text{H}}_2\text{(g)}$