GCSE Oxygen

Oxygen is the second most abundant gas in the atmosphere, making 21% of all the gases in the atmosphere.

Laboratory Preparation

The preparation of Oxygen is quite simple, and it is mainly a reaction that takes place in the liver, where oxygen is produced by the decomposition of hydrogen peroxide. In the lab the same reaction takes place, but a catalyst has to be used instead of the enzymes found in the body.

2H₂O₂ → 2H₂O + O₂

where Mn⁴⁺ is used as a catalyst

In order to test for Oxygen one should put a glowing splint which would relight in the presence of oxygen.

Combustion

Combustion is the process where any chemical reacts with oxygen to form an oxide. There can be either complete combustion or incomplete combustion, with the most common cases for incomplete combustion being in organic compounds.

Can you name the products of combustion of Hydrogen, Carbon, Sulfur, Magnesium, sodium and Iron?

Rusting

Iron can produce different oxides when it reacts with oxygen, but the one that reduces the strength of iron is rust. Rusting is the formation of Fe₂O₃ in the presence of water.

In order for rusting to take place, there are a number of criteria that have to meet, which are iron, oxygen and water.

Preventing rust is very important in everyday life. Some ways of rust prevention are the following:

• Painting can prevent water from reacting with the iron and therefore rust would be prevented.
• Sacrificial metal can be used so that it would react before the iron, This can be a magnesium piece which is more reactive than iron and therefore the magnesium would react with the oxygen and the iron would not form rust.

Ozone

Oxygen has got two different allotropes, O₂ and O₃ where O₃ is ozone and although it is toxic if inhaled it is one of the most important chemicals on earth since it stops UV rays from entering the atmosphere.

Ozone is produced from Oxygen through electricity:

3O₂ → 2O₃

Although one has to note that the reaction can go the other way with the use of certain gases which would break the ozone resulting in an equilibrium.

The ozone hole is due to the uses of CFCs (chlorofluorocarbons) which react with ozone to produce oxygen in the upper parts of the atmosphere.