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Oxygen is:

• colourless
• odourless
• denser than air
• exists as two oxygen atoms bonded together – diatomic O₂

Test for oxygen

A glowing splint applied to a sample of oxygen gas will relight.

Preparing oxygen

Oxygen can be made from hydrogen peroxide, which decomposes slowly to form water and oxygen:

hydrogen peroxide → water + oxygen

2H₂O₂(aq) → 2H₂O(l) + O₂(g)

The rate of reaction can be increased using a catalyst, manganese(IV) oxide. When manganese(IV) oxide is added to hydrogen peroxide, bubbles of oxygen are given off.

To make oxygen in the laboratory the same apparatus that was used for the preparation of hydrogen is used. Hydrogen peroxide is poured into a conical flask containing some solid manganese(IV) oxide. Hydrogen peroxide is colourless solution and manganese(IV) oxide is a black solid.

Instead of the gas jar and water bath, a gas syringe could be used to collect the oxygen.

Uses of oxygen

• Oxygen is used in medicine to help patients with breathing difficulties.
• In welding, acetylene gas is mixed with oxygen to increase the burn temperature to about 3000 degrees celsius. Oxyacetylene welding is used to cut and weld steel.