Write a preparation of dioxygen. Explain the physical and chemical properties of dioxygen. State uses of dioxygen.

(N/A) $(i)$ Laboratory preparation :
$(1)$ By thermal decomposition of salts such as chlorates,nitrates and permanganates.
$2 KClO_{3} \stackrel{\Delta}{\longrightarrow} 2 KCl + 3 O_{2}$
$2 NaNO_{3} \stackrel{\Delta}{\longrightarrow} 2 NaNO_{2} + O_{2}$
$2 KMnO_{4} \stackrel{\Delta}{\longrightarrow} K_{2}MnO_{4} + MnO_{2} + O_{2}$
$(2)$ By the thermal decomposition of the oxides of metals low in the electrochemical series and higher oxides of some metals.
$2 Ag_{2}O_{(s)} \stackrel{\Delta}{\longrightarrow} 4 Ag_{(s)} + O_{2(g)}$
$2 Pb_{3}O_{4(s)} \stackrel{\Delta}{\longrightarrow} 6 PbO_{(s)} + O_{2(g)}$
$2 HgO_{(s)} \stackrel{\Delta}{\longrightarrow} 2 Hg_{(l)} + O_{2(g)}$
$2 PbO_{2(s)} \stackrel{\Delta}{\longrightarrow} 2 PbO_{(s)} + O_{2(g)}$
$(3)$ By decomposition of hydrogen peroxide in presence of finely divided metals and manganese dioxide.
$2 H_{2}O_{2(aq)} \xrightarrow{MnO_{2}} 2 H_{2}O_{(l)} + O_{2(g)}$ ($MnO_{2}$ acts as catalyst)
$(ii)$ Commercial production : Industrially,dioxygen is obtained from air by first removing carbon dioxide and water vapour and the remaining gases are liquefied and fractionally distilled to give dinitrogen and dioxygen.
$(iii)$ On large scale it is prepared by electrolysis of acidulated water which releases hydrogen at cathode and oxygen at the anode.
$(A)$ Physical properties : Dioxygen is a colourless and odourless gas.
The water solubility is $3.08 \ cm^{3}$ per $100 \ cm^{3}$ water at $293 \ K$ which is just sufficient for the vital support of marine and aquatic life.
It has three stable isotopes: $^{16}O, ^{17}O, ^{18}O$.
It liquefies at $90 \ K$ and freezes at $55 \ K$.
Molecular oxygen,$(O_{2})$ is paramagnetic due to presence of unpaired electrons in $\pi^{*}$ orbitals.
$(B)$ Chemical properties :
$(i)$ Reaction with metals : Dioxygen directly reacts with nearly all metals except $Au$ and $Pt$ to form oxides.
For example :
$2 Ca + O_{2} \rightarrow 2 CaO$
$4 Al + 3 O_{2} \rightarrow 2 Al_{2}O_{3}$
$4 Fe + 3 O_{2} \rightarrow 2 Fe_{2}O_{3}$
$(ii)$ Reaction with non-metals:
$C + O_{2} \rightarrow CO_{2}$
$P_{4} + 5 O_{2} \rightarrow P_{4}O_{10}$
$(iii)$ Reaction with compounds :
$2 ZnS + 3 O_{2} \rightarrow 2 ZnO + 2 SO_{2}$
$CH_{4} + 2 O_{2} \rightarrow CO_{2} + 2 H_{2}O$
$2 SO_{2} + O_{2} \xrightarrow{V_{2}O_{5}} 2 SO_{3}$ (Catalytic oxidation)
$4 HCl + O_{2} \xrightarrow{CuCl_{2}} 2 Cl_{2} + 2 H_{2}O$ (Oxidation)
In addition to its importance in normal respiration and combustion processes,oxygen is used in oxyacetylene welding and in the manufacturing of steel.
Oxygen cylinders are used in hospitals,high altitude flying and in mountaineering.
The combustion of fuels,e.g.,hydrazines in liquid oxygen provides tremendous thrust in rockets.