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topic 7-organic chemistry (hydrocarbons (alkanes have c--c bonds (CnH2n+2,…
topic 7-organic chemistry
hydrocarbons
only
contain hydrogen and carbon atoms
alkanes have c--c bonds
CnH2n+2
the alkanes are a homologous series (group of organic compounds that react in a similar way
alkanes are saturated compounds- each carbon forms 4 single covalent bonds
methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10)
properties change as chain gets longer
the shorter the chain the more viscous it is
shorter chains are more volatile (lower boiling points)
shorter chains are more flammable
properties effect how they are used as fuels
complete combustian
hydrocarbon + oxygen---> carbon dioxide + water (+energy)
both carbon and fuel are oxidized
fractional distillation
crude oil is made over a long period of time
crude oil is a fossil fuel, formed by remains of plants and animals that have died and are buried in mud. over millions of years with high temp and pressure the remains turn into oil which is drilled for
fossil fuels are non renewable as they take a long time to make and are used up faster than they are formed
fractional distillation used to separate hydrocarbon fractions
crude oil is a mixture of lots of different alkanes
1) the oil is heated until most of it has turned into gas which enters fractionating column
2) in the column there is a temp gradient (cooler as you go up)
3) the longer chain hydrocarbons have high boiling points so condense quickly and drain out near the bottom, shorter chain hydrocarbons have lower boiling points so condense near top
uses and cracking of crude oil
uses of crude oil
oil provides fuel for transport (cars, trains etc)
the petrochemical industry uses some hydrocarbons from crude oil as feedstock to make new compounds for uses in polymers, solvents, lubricants
cracking
short hydrocarbons are flammable so make good fuels and are in high demand
longer chain hydrocarbons are turned into shorter hydrocarbons through cracking
cracking produces alkenes are alkanes
some of these products are useful as fuels such as petrol
different methods of cracking
cracking is a thermal decomposition reaction-breaking down molecules by heating them
1)heat long chain hydrocarbons to vaporize them
2) then the vapour is passed over a hot powdered aluminum oxide catalyst
3) the long chain molecules split apart on surface of catalyst
or can be done by mixing hydrocarbon with steam and then heat them to a v high temp-steam cracking
alkenes
alkenes have a c=c bond
c=c bond means that alkenes have 2 fewer hydrogens compare to alkanes containing same number of carbon atoms
unsaturated
the c=c bond can open up to make a single bond allowing two carbon atoms to bond with other atoms- make them v reactive
ethane, propene, butene, pentene
CnH2n
burn with a smoky flame
in large amounts of oxygen alkenes combust completely to produce only water and carbon dioxide
however if there is not enough oxygen they have incomplete combustion
incomplete combustion
alkene + oxygen---> carbon + carbon monoxide +carbon dioxide+ water
incomplete combustion results in a yellow smoky flame and less energy being released
reaction of alkenes
react via addition reactions
functional group= the molecule that determines how a substance will typically react
all alkenes have C=C functional group
in addition reactions double bond opens up to form single bond and a new atom is added to each carbon
addition of hydrogen is known as hydrogenation
hydrogen can react with double bonded carbons to open up the double bond and form a saturated alkane
reacted in presence of a catalyst
steam can react with alkenes to form alcohols
when steam reacts with alkenes, water is added across double bond so alcohol is formed
ethanol made by mixing ethane and steam and passing it over a catalyst
after reaction mixture is passed over condenser so ethanol and water condense and any ethane gas is recycled back into reactor
halogens can react with alkenes
alkenes will also react in addition reaction with halogens
the molecules becomes saturated and carbon forms a single bond with halogen atoms
addition polymers
plastics are made of long chain molecules called polymers
polymers are formed by monomers joining together- polymerization
polymerization needs high pressure and catalyst
monomers are normally alkenes
addition polymers and made from unsaturated monomers
the monomers that make up addition polymers have a double bond
alkenes open up their double bonds and join together to form polymer chains - addition polymerization
only one product formed in reaction
alcohols
alcohols have OH functional group
CnH2n+1OH
all alcohols contain OH functional group
first 4 have similar properties
alcohols are flammable, undergo complete combustion for carbon dioxide and water
they are soluble in water and have a neutral pH in solution
they also react with sodium to produce hydrogen
alcohols are oxidized by reacting with oxygen to produce a carboxylic acid
different alcohols form different carboxylic acids
alcohols are used for solvents and fuels
they can dissolve substances that water cannot dissolve such as oils and fats
the first 4 alcohols are used as fuels
ethanol can be made by fermentation
sugar (+yeast)---> ethanol + carbon dioxide
fermentation uses enzyme yeast to convert sugars into ethanol
fermentation happens fastest at 37 degrees in slightly acidic solution under anaerobic conditions
if conditions were different enzymes would be destroyed
carboxylic acids
have COOH functional group
names end in -anoic acid
methanoic acid, ethanoic acid, propanoic acid, butanoic acid
react like other acids
react with carbonates to produce salt, water and carbon dioxide
the salt formed ends in -anoate
e.g. ethanoic acid + sodium carbonate---> sodium ethanoate + water +carbon dioxide
carboxylic acids dissolve in water, when they ionize they release h+ ions resulting in an acidic solution- don't completely ionize so they form weak acidic solutions
esters can be made from carboxylic acids
esters have functional group COO
formed from an alcohol and carboxylic acid
an acid catalyst is usually used
alcohol +carboxylic acid---> ester +water
condensation polymers
polymers can be made by condensation polymerization
involves monomers which contain different functional groups
the monomers react together and bonds form between them making polymer chains
for each new bond formed a small molecule is lost (water)
addition and condensation polymerization are different
addition
only one monomer type containing C=C bond, one product formed, carbon- carbon double bond in monomer
condensation
two types of monomer each containing two of the same functional group or one monomer type with two different functional groups, two products formed, two reactive groups on each monomer
naturally occurring polymers
amino acids have an amino acid group and carboxyl group
an amino acid contains two different functional groups - basic amino group (NH2) and an acidic carboxyl group (COOH)
e.g. glycine
proteins are polymers of amino acids
amino acids form polymers known as polypeptides via condensation polymerization
the amino group can react with the acid group to form a chain and one molecule of water is lost
one or more long chain polypeptides are proteins- needed for enzymes, hemoglobin, antibodies, body tissue
DNA
dna contains genetic instructions that allow an organism to develop and operate
in a double helix structure
dna is made from two nucleotides (polymer strands) which contain bases (A,C,G,T)
the bases on different polymer chains cross link keeping the two nucleotides together and giving double helix structure
the bases acts as code for organisms genes
simple sugars can form polymers
sugars are small molecules that contain carbon, oxygen and hydrogen
sugars can react through polymerization to form larger carbohydrate polymers e.g. starch and cellulose