Chemistry GCSE unit 1

Organic chemistry is the study of carbon compounds.

Many organic compounds are to be found in crude oil.

Crude oil is a mixture of useful compounds. Fractional distillation separates crude oil intofractions.

The compounds within the different fractions differ by their carbon content, ease of burning, smell, colour, and melting/boiling point. The lighter fractions are smaller molecules and have lower boiling points. Petrol is one such fraction. The heavier fractions are long chained hydrocarbons with high boiling points. The lighter fractions are used as fuels and are hence in greater demand than the heavier fractions such as bitumen, which is used on roads.

Cracking is the process by which long chained compounds are broken down into smaller chained compounds.

Reforming is the process that changes chained molecules into branched.

The fractions are made up of hydrocarbons. Compounds that contain hydrogen and carbon only.

Alkanes are a family of hydrocarbons with the general formula. They are described as saturatedcompounds.

Alkenes are another family of hydrocarbons with the general formula. They are described as beingunsaturated due the presence of a double bond.

Both alkanes and alkenes carry out combustion in oxygen producing carbon dioxide and water.

Alkenes are more reactive than alkanes due to addition reactions occurring to their double bond. The alkanes are saturated so addition does not occur.

Polymerisation is a reaction whereby alkenes bond to one another forming long chains. The products of polymerisation are called polymers or plastics.

Alkenes readily carry out polymerisation as they can add to their double bonds

Metals often appear in the Earth's crust as an ore. An ore is the metal usually in the form of a compound, most commonly an oxide. When the ore is dug up, and decomposed to the metal alone, we call this extracting.

The more reactive a metal the more difficult to extract.

Unreactive metals, such as gold and silver can be found as pure elements in the Earth's crust.

There are different methods of extraction:

1. Eelectrolysis.

2. Heating with carbon monoxide.

3. Roasting in air.

Metals are a non-renewable resource. Hence, it is important to recycle used metals.

Aluminium is extracted from the ore bauxite, using electrolysis. At the cathode, aluminium is formed and at the anode oxygen gas forms.

Aluminium has many useful properties:

1. Shiny.

2. Good conductor of heat and electricity.

3. Malleable and ductile.

4. Low density.

Iron is extracted from the ore haematite (iron oxide) using a blast furnace.

Cast iron and steel are two useful by-products from the extraction of iron.

The corrosion of iron and steel is called rusting.

Rusting of iron occurs if both water and oxygen (usually from the air) is present.

To help prevent rust, several methods may be used:

1. Paint or grease.

2. Galvanising.

3. Sacrificial protection.

The atmosphere is a layer of gas around the Earth.

Air is a mixture of gases. It is most dense at sea-level and thins out as we rise through the layer of atmosphere called the troposphere.

The Earth formed about 4600 million years ago.

The ozone layer protects us from the Sun's most harmful ultraviolet rays.

The atmosphere is maintained by nature recycling substances in living things. All living things depend upon oxygen, nitrogen, carbon dioxide and water.

he Earth's surface is formed and forever changing by different processes occurring.

Igneous rocks are formed from the hot liquid rock (molten magma) from volcanoes solidifying. Interlocking crystals are often found in these rocks.

Sedimentary rock is formed from sediments. Due to weathering and erosion, larger rock may crumble into smaller ones and be transported until they eventually settle on sea or riverbeds. Over the years these fragments of rock compress together. Sedimentary rock is often crumbly due to its formation from small bits of rock. Often they are layered, and on some occasions fossils may be present.

Metamorphic rock occurs when heat or pressure or both cause a rock to change its structure.