Science - Chemistry

Crude oil is a mixture of hydrocarbons. A hydrocarbon is a compound that contiains only hydrogen and carbon atoms. Crude oil can be seperated into parts by fractional distillation. Each fraction contains hydrogen molecules with a similar number of carbon atoms. The fractioning column process:

• Oil is evaporated by heating it
• It is allowed to condense at different temperatures
• Fractions with low boiling points and viscosity exit at the top of the column
• Fractions with high boiling points and viscosity exit at the bottom of the column

The more carbon atoms in a hydrocarbon the more viscosity it has, the higher the boiling point, the less volatile and flammable it is.

Hydrocarbon

No. of Carbon Atoms

Hydrocarbon

No. of Carbon Atoms

Refinery gases

1 – 4

Diesel oil

15 – 22

Gasoline

5 – 6

Lube oil

20 – 30

Naphtha

6 – 10

Fuel oil

30 – 40

Kerosene

10 – 16

Bitumen

50+

Dry air is a mixture of nitrogen, oxygen and carbon dioxide. oxygen and nitrogen can be obtained by seperating them from liquid air through fractional distillation.

Fuel releases usefulamounts of energy when burnt. Many fuels are hydrocarbons. When fuels burn they react with oxygen from air. This is combustion. The fuel mus be alight to react. Complete combustion happens when there is plenty of oxygen available. Complete combustion of a hydrocarbon produces carbon dioxide and water and energy is released. Methane + oxygen = carbon dioxide + water. Incomplete combustion happens when a fuel burns without oxygen. Incomplete combustion produces carbon monoxide.

Limestone is calcium carbonate. It is used for construction (57%), concrete/cement (22%), glass (16%) and steel/iron alloys (5%). It is heated in lime kilns at high temperatures and decomposes into calcium oxide and carbon dioxide to form quicklime. Quicklime is a vital ingredient of cement, concrete and most glass. 

      Water + quicklime = slaked lime                water + calcium oxide = calcium hydroxide

All chemical elements are made up of atoms which have a nucleus of protons and neutrons and electrons surrounding the nucleus. All atoms of the same elements have the same number of protons and electrons in each atom.

                              Atomic Particle          Relative Charge

                              Proton                       + 1 (positive)

                              Neutron                     0 (no charge)

                              Electron                    - 1 (negative)

In a chemical reaction, atoms are rearranged to form different substances. Atoms are not created or destroyed. The same number of atoms are present before and after the reaction, however they are just joined to make a different combination. The total mass of atoms involved stays the same. Thermal decomposition is when metal carbonates decompose when they are heated and form an oxide and a carbon dioxide. Some decompose more easily than others (decomposition at a low temperature). 

Copper carbonate is the easiest to decompose. After that is zinc carbonate and then calcium carbonate which is the hardest to decompose. Precipitation reaction occurs when two soluble substances react and form an insoluble substance. The insoluble product is the precipitate for example: 

Key: s - soluble

        i - insoluble

lead nitrate (s) + potassium iodide (s) = potassium nitrate (s) + lead iodide (i)

The Lifecycle of Carbon Dioxide

Organisms trap carbon dioxide as they photosynthesise. They then die and fossilise. Eventually these become fossil fuels and are burnt. Carbon dioxide is released into the atmosphere again.

Compounds and Formulae

An element is a substance that can't be split into a simpler substance. Atoms are the smallest part of an element that can take part in chemical reactions. Amolecule is two or more atoms joined together. Compounds are substances that consist of atoms of different elements joined together. A mixture contains different elements or compouds but aren't chemically joined. In a chemical reaction the atoms in the reactants are changed to make different products. Elements have there own chemical symbol. The formula of a compound shows the symbols of the elements it contains and the numbers of their atoms in the molecules. Iron compounds such as iron sulfide and iron carbonate formed. These only form when there is NO oxygen. Iron oxide is formed when only a small amount of oxygen is available. A different form of iron oxide came about; one that needs more oxygen.

Rocks make up the Earth's crust. Igneous rocks are formed when magma or lava solidifies and are made up of interlocking crystals which makes them hard to erode. They can have either large or small crystals. Small crystals are formed if it solidifies quickly and large ones when it solidifies slowly. Examples of this are basalt and granite respectively. Sedimentary rocks are formed when sediment is squashed together. It erodes easily as there are no interlocking crystals. Theyare made up of rounded grains and can contain fossils. They include chalk and limestone which are both natural forms of calcium carbonate. Metamorphic rocks are formed under heat and pressure. Marble is formed from chalk or limestone and is a natural source of calcium carbonate.