Dioxygen

a. Preparation

i. Laboratory methods :

• By heating oxygen containing salts such as chlorates, nitrates and permanganates.

• By thermal decomposition of oxides of metals.

• By decomposition of hydrogen peroxide in the presence of a catalyst such as finely divided metals and manganese dioxide.

ii. Electrolysis : Dioxygen can be prepared on a large scale by the electrolysis of water, when hydrogen is liberated at the cathode and oxygen at the anode.

iii. Industrial method : Dioxygen is obtained from air, by first removing carbon dioxide and water vapour. The remaining gases are liquified subsequently. This is followed by fractional distillation, which gives dinitrogen and dioxygen.

b. Physical properties :

• Dioxygen is a colourless and odourless gas.
• Dioxygen is sparingly soluble in water: 30.8 cm³ of $\mathrm{O_2}$ dissolves in 1000 cm³ of water at 293 K. A small amount of dissolved dioxygen is sufficient to sustain marine and aquatic life.
• It liquifies at 90 K and freezes at 55 K.
• Oxygen has three stable isotopes: $^{16}$O, $^{17}$O and $^{18}$O.
• Molecular oxygen, $\mathrm{O_2}$, exhibits paramagnetism.

c. Chemical Properties : (the book's own bold sub-heading prints as "Chemcial Properties :")

i. Reaction with metals : Dioxygen directly reacts with almost all metals except Au and Pt to form their oxides.

ii. Reaction with nonmetals : Dioxygen reacts with nonmetals (except noble gases) to form their oxides.

iii. Reaction with some compounds :

$\mathrm{4HCl + O_2 \xrightarrow[\Delta]{CuCl_2} 2Cl_2 + 2H_2O}$ …