Crude Oil and Homologous Series

crude oil

• a mixture of hydrocarbons

• source of useful substances

• a finite resource

hydrocarbon

a molecule that contains only hydrogen and carbon

fraction

molecules with similar boiling points and chain lengths

fractional distillation of crude oil

• crude oil enters fractionating column as a vapour

• column is hotter at the bottom and colder at the top

• the vapours rise in the column and cool down

• when they reach their boilng point they condense and are removed as liquids

fractions of crude oil + uses

• gas - cooking

• petrol - cars

• kerosene - aeroplanes

• diesel oil - lorries

• fuel oil - ships

• bitumen - roads

smaller fractions of crude oil

• lower boiling point - easier to break up, weak intermolecular forces

• less volatile - easier to evaporate so easier to ignite

• less viscous - easier to pour, weak intermolecular forces

larger fractions of crude oil

• higher boiling point - harder to break up, strong intermolecular forces

• more volatile - harder to evaporate so easier to ignite

• more viscous - harder to pour, weak intermolecular forces

homologous series

• differ by -CH₂ each time

• have similar chemical properties

• have a trend in physical properties

• have the same general formula

alkane

saturated hydrocarbons

general formula for alkanes

C_nH_2n+2

complete combusition

• plenty of oxygen

• produces carbon dioxide and water

incomplete combustion

• limited oxygen supply

• produces water and either carbon monoxide or soot (C)

carbon dioxide (CO₂)

• is a green house gas, causes global warming

• e.g. rising sea levels

carbon monoxide (CO)

• toxic

• reduces ability of haemoglobin to bind to oxygen

soot (C)

• can cause breathing difficulties

• can cause global dimming

sulphur dioxide (SO₂)

• sulphur impurities burn with hydrocarbon and react with oxygen

• SO₂ gas is formed and dissolves in clouds to form sulphurous acid which oxidises to form sulphuric acid

• rain water becomes acidic and acid rain is formed

nitrogen oxides (NO_x)

• formed from nitrogen and oxygen in the air reacting together at high temperatures (e.g. car engines)

• causes acid rain

acid rain

• makes lakes acidic and kills fish

• damages buildings

• kills trees

alkenes

unsaturated hydrocarbons

general formula for alkenes

C_nH_2n

test for alkenes

add bromine water and shake

cracking

• splitting apart longer less useful alkanes to make short more useful alkanes

• also makes alkenes

conditions for cracking

• 450°C

• a catalyst (silica SiO₂/alumina Al₂O₃)