From The Student Room

TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Biology > Atmosphere and Pollution

---

Contents 1 History 2 Current composition 3 Identifying the products of combustion 4 Comments

History

Initially, the atmosphere was probably mainly carbon dioxide, with water vapour and small quantities of methane and ammonia.

The Earth cooled and the water vapour condensed to form the oceans. Plants started to evolve and photosynthesise to produce oxygen.

Carbon from the carbon dioxide became locked up in sedimentary rocks and fossil fuels (coal, oil, and gas).

Methane and ammonia reacted with the oxygen to produce nitrogen. Nitrogen was also released into the atmosphere from living organisms, including denitrifying bacteria.

The formation of oxygen in the atmosphere resulted in the development of an ozone (O₃) layer. This filters out harmful UV radiation from the sun allowing living organisms to develop and evolve.

Current composition

• Nitrogen - 78%

• Oxygen - 21%

• Argon, carbon dioxide and other gases - 1%

These proportions are maintained due to the carbon and nitrogen cycles.

Burning of fossil fuels lead to the production of carbon dioxide, sulphur dioxide and nitrogen oxides.

Carbon dioxide is a Greenhouse gas. This prevents heat from leaving the earth, leading to a gradual warming of the earth.

Sulphur dioxide and nitrogen oxides dissolve in the water in the atmosphere to form acid rain, which damages buildings, plants, rivers and lakes.

Identifying the products of combustion

Combustion is reaction with oxygen. (commonly burning).

The following can be used to test for the products of combustion:

(Need a diagram of the apparatus and the list of chemicals needed)

A water pump is used to draw air and combustion products through the apparatus.

Anhydrous copper sulphate tests for the presence of water, and turns from white to blue.

Limewater tests for the presence of copper sulphate, and turns cloudy.

The anhydrous copper sulphate is placed first to prevent any water from the limewater affecting the test for the presence of water.

Combustion of fuels produces carbon dioxide and water when a plentiful supply of oxygen is used. If the supply of oxygen is limited then incomplete combustion occurs and carbon monoxide (which is toxic) and carbon (soot) can be produced.

Comments