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).
alkene + hydrogen
alkane.
this is because double bond is broken. it requires a catalyst
alkene + water
conditions: presence of a catalyst and high temperatures
an alcohol due to the “OH” group
alkene + halogen
no catalyst needed. same sor of reaction as with hydrogen except alkane is not formed.
functional group of alcohol and formula
- OH
Cn H2n+1 OH
methanol, ethanol, propanol, butanol
how do alcohols react with sodium? eg methanol
sodium + methanol -> sodium methoxide +hydrogen
they produce hydrogen gas and a metal salt.
how do alcohols react when burnt in air?
in complete combustion they form carbon dioxide and water
alcohol +oxygen -> carbon dioxide + water
how do alcohols react with oxygen?
alcohol + oxygen -> carboxylic acid + water
eg ethanol will produce ethanoic acid, which is used in vinegar
funtional group of carboxylic acids?
- COOH
methanoic acid, ethanoic acid, propanoic acid, butanoic acid.
ethanoic acid would be: CH3COOH
(carbon from functional group is counted).
carboxylic acid + metal
metal carboxylate salt + hydrogen
carboxylic acid + carbonate
metal carboxylate salt, water and carbon dioxide gas.
salts formed by a carboxylic acid names
end in anoate so
methanoate, ethanoate, propanoate, butanoate
ethanoic acid + magnesium
magnesium ethanoate + hydrogen
propanoic acid + potassium hydroxide
potassium propanoate + water
butanoic acid + potassium carbonate
potassium butanoate + water + carbon dioxide
alcohol + carboxylic acid
esther + water
ethanol + ethanoic acid
ethyl ethanoate + water
why are carboxylic acids weak acids in terms of ionisation and pH?
it only partially ionises in aqueous solution
what is addition polymerisation?
when many small molecules (monomers) join together to form very large molecules (polymers).
this is seen in alkenes - they can be used to make polymers like poly(ethene) or poly(propene)
what is condensation polymerisation?
it involves monomers with two functional groups. when these types of monomers react, they join together, usually losing small molecules such as water and so the reaction is called condensation reactions.
difference between addition polymerisation and condensation polymerisation
addition forms the polymer molecule only.
condensation forms the polymer molecule and a water molecule per linkage
ethanediol + hexanedioic acid
polyester (a condensation polymer) + water
when can condensation polymer happen?
when each of the monomers have at least two functional groups
and when two of these functional groups are different overall.
and a small molecule is given off in the process
amino acids
they have two different functional groups in a molecule
they react by condensation polymerisaion to prouce polypeptides.
what is DNA?
a large molecule essential for life. it encodes genetic instructions for the development of living organisms and viruses
structure of DNA
two polymer chains, made from four different monomers called nucleotides, in the form of a double helix
what are some other naturally occuring polymers?
proteins - made of monomers of amino acids
cellulose, starch - polysaccharides. made up of simple sugar monomers.
how can ethanol be produced? two ways
ethene + steam -> ethanol (addition reaction)
glucose -> ethanol + carbon dioxide (fermentation)
conditions for addition reaction for ethene?
a catalyst and high temperatures are required
conditions for fermentation?
anaerobic conditions (no oxygen)
warm temps - 30-40 (optimum conditions for enzymes)
yeast cells
uses of ethanol?
as chemical feedstock to produce other organic compounds]
in alcoholic drinks
can be burned and used as biofuel
addition reaction ethanol balanced equation?
C2H4 + H2O -> C2H5OH
fermentation reaction balanced equation?
C6H12O6 -> CH3CH2OH + CO2
