Oxygen

GCSE Oxygen

Oxygen is a gas found in the atmosphere with a boiling point of -183⁰C.

Ozone

Oxygen is found as 2 allotropes, O₂ and O₃, with the latter being called ozone. Ozone is much different than atmospheric oxygen, and its structure is the following:

Since the structure of O₂ and O₃ are different thees would then have different reactivities.

There are two places in which this reaction can take place:

In the stratosphere where the ozone layer is present and it shields against UV light.

At sea level where it is considered a carcinogen and a pollutant.

Preparation of Oxygen

Oxygen can be prepared via a number of ways, some of which can be even prepared in a laboratory.

These include:

• Reaction of peroxides with water.
• Fractional distillation of air.
• Heating oxides of metals which have a low reactivity.
• Heating oxides of metals with a high oxidation state.
• Reduction of hydrogen peroxide and chlorates both in the presence of MnO₂.

Properties of Oxygen

Oxygen also has a number of properties:

• Aireal oxidation
• Combustion of hydrocarbons.
• Burning metals in air.
• Burning non-metal in air.

Oxides

Metal oxides

There are 2 types of metal oxides:

Basic: MgO, CuO, CaO

Amphoteric: Al₂O₃, ZnO, PbO, SnO, SnO₂

Covalent oxides

There are 2 types of covalent oxides:

Acidic: CO_2, SO₂, SO₃, NO₃, B₂O₃, P₂O₃, P₂O₅

Neutral: CO, NO, F₂O

Normal oxides

A normal oxide is one in which the Oxygen either gains 2 electrons from a metal atom or shares 2 electrons with a non-metal.

Peroxides

In peroxide, Oxygen has a single bond to another Oxygen, forming an O₂^2- ion.

Mixed oxide

A mixed oxide is one in which the metal has an equal ratio of 2 metal oxides, such as Fe₂O₃ and FeO mixture to give Fe₃O₄.

Hydrogen peroxide

Hydrogen peroxide is a liquid at room temperature due to extensive hydrogen bonding. It is prepared by the action of sulfuric acid on barium peroxide at 0⁰C. Other peroxides can also be sued but the reaction would be too dangerous.

BaO_2(S) + H₂SO₄ → BaSO_4(s) + H₂O₂

Barium peroxide is added in excess in order to remove the 2 solids by filtration.

If the temperature is above 0^oC the peroxide will start to decompose to form Oxygen

Hydrogen peroxide can act both as a reducing agent and as an oxidising agent:

Reducing agent:

H₂O₂ → O₂

MnO₄^2- → Mn²⁺

ClO^– → Cl^–

Oxidising agent:

H₂O₂ → H₂O

Fe²⁺ → Fe³⁺

PbS → PbSO₄  (black to white ppt.)