organic chemistry Flashcards
what is crude oil?
a finite resource that is found in rocks. it is the remains of an ancient biomass consisting mainly of plankton that was buried in mud.
it is a mixture of a very large number of compounds (mainly hydrocarbons)
what are hydrocarbons?
molecules that are made up of hydrogen and carbon only
what is the general formula for alkanes, and give the first four alkanes
Cn H2n+2
methane - CH2
ethane - C2H6
propane - C3H8
butane - C4H10
how can the hydrocarbons in crude oil be seperated?
by fractional distillation, they are seperated into fractions. each fraction contains groups of hydrocarbons that have similar chain lengths.
describe the process of fractional distillation of crude oil
- its carried out in a fractionating column that is hot at bottom and cool at top.
- the crude oil enters the fractionating column and is heated so the vapours rise.
- the hydrocarbon vapours that have high boiling points will immediatley condense into liquide lower down, and are tapped off at the bottom of the column
- vapours with low boiling points rise to the top of the column and condense at top to be tapped off.
where are the smaller and bigger chained hydrocarbons collected in the fractionating column?
smaller chained - at the top
longer chained - at the bottom
what is crude oil used for in the industry?
used for fuels and feedstock
fuels - petrol, diesel, kerosene, petroleum, heavy fuel oil
other - solvents, lubricants, polymers, detergents
how boiling point of hydrocarbons changes
as molecules get larger, the intermolecular forces of attraction between the molecules becomes greater because there are more electrons in the molecules and greater surface area contact between them.
this means that more heat is needed to seperate the molecules, hence with increasing molecular size, the boiling point increases
how does viscosity of a hydrocarbon change and what is viscosity
high viscosity would mean that liquids are thick and flow less easily
as chain length increases, so does the viscosity.
this would mean that longer chained alkanes are useful as lubricants as they are less likely to burn
how does flamability change with hydrocarbons?
the smaller the chain of a hydrocarbon, the more flammable it is. this makes them useful as fuels, releasing large amounts of energy when burned.
what happens when hydrocarbons are combused
the combustion of hydrocarbon fuels releases energy. the complete combustion of a hydrocarbon produces carbon dioxide and water.
why is cracking done?
it is done to produce smaller, more useful molecules from a large hydrocarbon molecule.
this is because there is a high demand for fuels with small molecules and so some of the produts of cracking are useful as fuels
what does cracking produce?
an alkane and an alkene
describe catalytic cracking
the hydrocarbon molecules are heated to high temperatures. then the vapours are passed over a hot, powdered catalyst of aluminium oxide.
this causes the molecules to be broken up so smaller alkanes and alkenes are produced.
describe steam cracking
after the hydrocarbons have been vapourised, they are mixed with steam and heated to very high temperatures again.
this causes the long chain to split apart into a small alkane and an alkene.
what is the equation for an alkene?
Cn H2n
ethene
propene
butene
pentene
what are alkenes used for?
used to produce polymers and as starting materials for the production of many other chemicals.
alkene test
bromine water is added to a solution of alkenes, and it turns it from orange to colourless
why are alkenes unsaturated?
they contain two fewer hydrogen atoms than alkanes with the same number of carbon atoms
how do alkenes react with oxygen in a combustion reaction?
they react in the same way as other hydrocarbons.
when there is innsufficient amounts of oxygen, incomplete combustion happens so carbon monoxide is produced, or just carbon (in the form of soot).
