Question

Chloride of a metal (X) which is used to make coins when exposed to sunlight, turns grey from white. Name the type of reaction and identify X.

Answer 1

1. Type of reaction

Combination reaction: Reaction in which two or more reactants combine to form a single product. $\mathrm{A}+\mathrm{B}\to \mathrm{C}$

Decomposition reaction: Reaction in which reactant is broken down into two or more products in the presence of heat, light or electricity. $\mathrm{A}\to \mathrm{B}+\mathrm{C}$

Displacement reaction: Reaction in which one of the higher reactive element displaces a less reactive element from its solution. $\mathrm{A}+\mathrm{BC}\to \mathrm{AC}+\mathrm{B}$ ( Here A is more reactive than B)

Double displacement reaction: Reaction in which ions of both the reactants interchange their place and form new compounds. $\mathrm{AB}+\mathrm{CD}\to \mathrm{AD}+\mathrm{CB}$

2. Reaction:

$2\mathrm{AgCl}\left(\mathrm{s}\right)\stackrel{\mathrm{sunlight}}{\to }2\mathrm{Ag}\left(\mathrm{s}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)$

Silver chloride Silver Chlorine

(white) (grey)

The metal used in making coins is silver and its chloride is $\mathrm{AgCl}$.

In presence of sunlight $\mathrm{AgCl}$ which is white colour solid undergoes photochemical decomposition that is it breaks down into $\mathrm{Ag}$ which is grey in colour and ${\mathrm{Cl}}_2$ gas is released which is yellowish-green in colour.

So it is a type of decomposition reaction and X is $\mathrm{Ag}$.