Explain the preparation of ozone. Explain the properties of ozone and state its uses.

(N/A) Preparation: When a slow dry stream of oxygen is passed through a silent electrical discharge, a conversion of oxygen to ozone $(10 \%)$ occurs. The product is known as ozonised oxygen.
$3 O_{2(g)} \rightarrow 2 O_{3(g)}$; $\Delta H^{\circ} = +142 \ kJ \ mol^{-1}$
Since the formation of ozone from oxygen is an endothermic process, it is necessary to use a silent electrical discharge in its preparation to prevent its decomposition.
Physical Properties: Pure ozone is a pale blue gas, dark blue liquid, and violet-black solid. It has a characteristic odour. Ozone has two resonating structures. The two oxygen-oxygen bond lengths are identical $(128 \ pm)$ and the bond angle is $117^{\circ}$. Its molecular shape is angular (bent).
Chemical Properties:
$1$. Oxidising agent: $PbS_{(s)} + 4 O_{3(g)} \rightarrow PbSO_{4(s)} + 4 O_{2(g)}$
$2$. Reaction with iodide ions: $2 I^-_{(aq)} + H_2O_{(l)} + O_{3(g)} \rightarrow 2 OH^-_{(aq)} + I_{2(s)} + O_{2(g)}$
$3$. Ozone layer depletion: $NO_{(g)} + O_{3(g)} \rightarrow NO_{2(g)} + O_{2(g)}$
Uses: It is used as a germicide, disinfectant, and for sterilising water. It is also used for bleaching oils, ivory, flour, and starch. It acts as an oxidising agent in the manufacture of potassium permanganate.