Question

During the reaction of some metals with dilute hydrochloric acid, the 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 gas are seen when lead (Pb) is reacted with the acid.

Explain these observations giving suitable reasons.

Answer 1

Explanation

The reactivity series is the arrangement of metals on the decreasing order of activity of the metal.

The order will be potassium, sodium, calcium, magnesium, aluminium, zinc, iron, tin, lead, hydrogen, copper, silver, and gold.

(a) Silver $\left(\mathrm{Ag}\right)$ is placed below hydrogen in the activity series. It cannot replace hydrogen from dilute $\mathrm{HCl}$ and no chemical reaction is possible.

(b) The reaction of $\mathrm{Al}$ with dilute $\mathrm{HCl}$ is exothermic, which means that heat is produced during the process, raising the temperature of the reaction mixture.

$2\mathrm{Al}\left(\mathrm{s}\right)+6\mathrm{HCl}\left(\mathrm{aq}\right)\to 2{\mathrm{AlCl}}_3\left(\mathrm{aq}\right)+3{\mathrm{H}}_2\left(\mathrm{g}\right)$

(c) Sodium is a highly reactive metal it reacts with atmospheric oxygen to form an exothermic reaction which results in a temperature increase.

$2\mathrm{Na}\left(\mathrm{s}\right)+2\mathrm{HCl}\left(\mathrm{aq}\right)\to 2\mathrm{NaCl}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$

(d) When lead reacts with acid it produces Hydrogen gas which is responsible for the formation of bubbles.

$\mathrm{Pb}\left(\mathrm{s}\right)+2\mathrm{HCl}\left(\mathrm{aq}\right)\to {\mathrm{PbCl}}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{s}\right)$