1. It is neutral to litmus paper
2. Oxygen gas liquefies at -183°C and solidifies at -225°C
3. It is slightly soluble in water
4. It is a colorless, odorless and tasteless gas
5. It has about the same density as air

1. Combustion: Hydrocarbons burn in oxygen to yield carbon (IV) oxide and water. $$CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O $$
2. Direct combination with metals: Oxygen conbines with most metals except gold, mercury and silver to yield basic oxides. $$ 4K + O_2 \rightarrow 2K_2O $$ $$ 2Ca + O_2 \rightarrow 2CaO $$ $$ 4Na + O_2 \rightarrow 2Na_2O $$ $$2Mg + O_2 \rightarrow 2MgO $$ The oxides of Sodium, potassium and calcium dissolve in water to form alkalis. $$ CaO + H_2O \rightarrow Ca(OH)_2 $$ $$ K_2O + H_2O \rightarrow 2KOH $$ $$ Na_2O + H_2O \rightarrow 2NaOH $$
3. Direct combination with Non-metals: Oxygen combines with some non-metals like sulphur, carbon, nitrogen and phosphorus to produce acidic oxides. $$ S + O_2 \rightarrow SO_2 $$ $$ C + O_2 \rightarrow CO_2 $$ $$ P_4 + 3O_2 \rightarrow P_4O_6 $$ These acidic oxides dissolve in water to produce acids hence they are also called acid anhydrides. $$ SO_2 + H_2O \rightarrow H_2SO_3 $$ $$ CO_2 + H_2O \rightarrow H_2CO_3 $$ $$ P_4O_6 + 6H_2O \rightarrow 4H_3PO_4 $$
4. Oxidation: Glucose is oxidized during respiration by oxygen to yield carbon (IV) oxide. $$ C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O $$
5. Rusting: Oxygen reacts with iron in the presence of moisture to produce reddish brown iron (III) oxide.
$$ 4Fe + 3O_2 + xH_2O \rightarrow 2Fe_2O_3.xH_2O $$
6. Reaction with Nitrogen: Oxygen reacts with Nitrogen during lightning flashes to yield Nitrogen (II) oxide. $$ N_2 + O_2 \rightarrow 2NO $$

Place a glowing splint over a sample of the unknown gas. If the splint is rekindled, the gas is likely oxygen gas.

However, Dinitrogen (I) oxide \( N_2O \) also behaves similarly. The table below shows how these gas can be identified.

1. Liquid oxygen is commonly used as rocket propellant in space exploration due to its ability to support combustion.
2. Oxygen is used to aid breathing artificially.
3. Oxygen combined with ethyne is used to produce oxy-ethyne flames which is used for cutting and melting metals.
4. Oxygen is used in the manufacture of important chemical compounds like ethanoic acid, tetraoxosulphate (VI) acid, e.t.c
5. Oxygen is employed in water treatment processes to eliminate impurities and enhance the quality of water.
6. In metallurgical processes, oxygen is often used to refine and extract metals from their ores.
7. In steel industry, oxygen is used to remove carbon, sulphur and phosphorus in the L-D process for steel production.