Properties of Oxygen

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Physical Properties of Oxygen

Oxygen (or dioxygen) has the following physical properties.

• Oxygen is colorless, odorless and a tasteless diatomic gas under normal conditions.

• Oxygen is slightly heavier than air. Its density relative to air is 1.1053.

• Oxygen is sparingly soluble in water. 30 mL of oxygen in one liter of water at STP. This small amount of dissolved dioxygen is sufficient to sustain marine and aquatic life and for the destruction of organic wastes in water bodies.

• Oxygen boils at -183°C (90 K) and solidifies at -218°C (55 K).

• Oxygen is paramagnetic in nature and liquefies to give pale blue liquid.

• Metals such as silver, gold and platinum adsorb oxygen gas at 500°C. Molten silver absorbs ten times its mass of oxygen and expels it rapidly on cooling. This phenomenon is called the spitting of silver.

The important physical values of atomic and molecular oxygen are listed below.

Chemical Properties of Oxygen

Oxygen (dioxygen) is neutral and has no action towards blue or red litmus. It is a supporter of combustion. Oxygen is quite a stable compound due to high bond (dissociation) energy of O = O bond. Its bond energy is 495 kJ mol^-1. So,

As a result, oxygen requires initial heating in its reactions (except with highly electro-positive metals). The reaction of other elements with oxygen is exothermic. Once the reaction starts, it continues on its own, as the heat generated during the process is sufficient to sustain the reaction. Some typical chemical reactions of oxygen are described.

Reaction with metals

All metals form oxides with oxygen. The reaction conditions and the type of oxide formed are determined by type of metal.

Sodium and calcium

These react with oxygen at room temperature to form respective oxides.

These oxides are basic in nature and react with water to give the corresponding alkali.

Sodium at 575 K forms peroxide with oxygen.

Magnesium

Magnesium burns in air exothermally to form magnesium oxide

Metals like zinc, iron and aluminium

They react with oxygen only on heating strongly. The reactions are exothermic in nature.

Iron in the presence of moisture (water) and air undergoes rusting. Rust is reddish-brown hydrated iron oxide.

Reaction with non-metals

Oxygen reacts with a number of non-metals to form their respective oxides.

With hydrogen

With nitrogen

With sulphur

With carbon

With phosphorus

As the oxides of non-metals are acidic in nature, when dissolved in water, the resulting solution is acidic in nature and it turns blue litmus red.

Reaction with compounds

Oxygen (or dioxygen) oxidizes many compounds under suitable conditions.

Hydrogen chloride gets oxidized to chlorine

Ammonia gets oxidized to nitric oxide

This reaction forms the basis of manufacturing nitric acid from ammonia (Ostwald's process).

Sulphur dioxide oxidizes to sulphur trioxide

This reaction forms the basis of Contact process for the manufacture of sulphuric acid.

With carbon disulphide, carbondioxide and sulphur dioxide are liberated

Metal sulphides get oxidized to corresponding oxides liberating sulphur dioxide.

Hydrocarbons get oxidized to carbondioxide and water.

Uses of oxygen

Oxygen has varied industrial and scientific uses.

• Oxygen (or dioxygen) is used in steel making

• It is also used in oxy-hydrogen and oxy-acetylene welding torches.

• Oxygen is used as an oxidizer in rocket propellants and in fuel cells.

• It is used for preparing oxygen containing organic compounds, such as ethylene oxide, phenol, etc.

• For medical purposes where O₂ is required for emergency operations and respiratory/cardiac collapses.