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organic chemistry (alcohols (used as solvents & fuels (e.g. methanol…
organic chemistry
alcohols
alcohols are flammable & undergo complete combustion in air to produce carbon dioxide & water e.g. 2CH3OH9(l) +3O2(g) --> 2CO2 + 4H2O
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used as solvents & fuels
e.g. methanol & ethanol used as solvents in industry as they can dissolve most things water can dissolve but also substances water can't dissolve e.g. hydrocarbons, oils & fats
first 4 alcohols used as fuels e.g. ethanol used as a fuel for spirit burners - burns fairly cleanly & odourless
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hydrocarbons
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alkanes
- CnH2n+2
- a homologous series - a group of organic compounds that react in a similar way
- saturated compounds - each carbon atom forms 4 single covalent bonds
- first 4: methane, ethane, pentane, butane
- have all C-C single bonds
properties change with length:
- the shorter the carbon chain, the less viscous the hydrocarbon is (more runny) / low viscosity + the more volatile it is (lower boiling point) + the more flammable the hydrocarbon is.
short chain hydrocarbons with lower boiling points are used as 'bottled gases' - stored under pressure as liquids in bottles.
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reactions of alkenes
hydrogenation
addition of hydrogen
hydrogen can react with the double-bonded carbons to open the double bond & form the equivalent, saturated, alkane.
the alkene is reacted with hydrogen in the presence of a catalyst.
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alkenes
unsaturated as they have a double carbon-carbon bond between two of the carbon atoms & have two fewer hydrogen atoms than alkanes with the same number of carbon atoms --> unsaturated
the C=C double bond can open up to make a single bond, allowing the two carbon atoms to bond with other atoms, making alkenes reactive (more reactive than alkanes)
ethene, propene, butene, pentene
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in a large amount of oxygen, alkenes combust completely to produce only water & carbon dioxide but there isn't enough oxygen in the air so they tend to undergo incomplete combustion also producing carbon & carbon monoxide which is poisonous gas.
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incomplete combustion results in a smoky yellow flame & less energy being released compared to complete combustion of the same compound
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carboxylic acids
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react like other acids with carbonates to produce a salt, water & carbon dioxide --> salts formed end in '-ethanoate' e.g. methanoic acid forms methanoate
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esters have functional group '-COO-'
formed from an alcohol and a carboxylic acid.
an acid catalyst usually needed (e.g. concentrated sulfuric acid)
alcohol + carboxylic acid --> ester + water
ethanol + ethanoic acid --> ethyl ethanoate
CH3COOH + C2H5OH --> CH3COOC2H5 + H2O
fractional distillation
crude oil
fossil fuels e.g coal, gas, oil are non-renewable as they take so long to make that they are being used up much faster than they are being formed.
finite resources
a fossil fuel formed from the remains of plants & animals, mainly plankton, that died millions of years ago and were buried in mud.
over millions of years, with high temperature & pressure, the remains turned into crude oil which can be drilled up from the rocks where it's found.
crude oil is a mixture of different hydrocarbons (mostly alkanes) & the different compounds are separated by fractional distillation
- the oil is heated until most of it has turned into gas. the gas then enters a fractionating column (liquid bit drained off)
- there is a temperature gradient in the column (hotter at bottom)
- the longer hydrocarbons have higher boiling points so condense back into liquids & drain out of the column earlier, near the bottom.
- the shorter hydrocarbons have lower boiling points so condense & drain out later on, near the top of the column where it is cooer.
- the crude oil is separated into different fractions, each fraction contains a mixture of hydrocarbons that all contain a similar number of carbon atoms, so have similar boiling points
condensation polymers
addition polymerisation:
- only one monomer type containing a C=C bond
- only one product formed
- carbon-carbon double bond in monomer (functional group)
condensation polymerisation:
- two monomer types each containing two of the same functional groups OR one monomer type with two different functional groups.
- two types of product - polymer & a small molecule e.g. water
- two reactive groups on each monomer (functional groups)
involves monomers which contain different functional groups. the monomers react together & bonds form between them, making polymer chains.
for each new bond that forms, a small molecule (e.g. water) is lost --> condensation polymerisation.
simplest types of condensation polymers contain two different types of monomer, each with two of the same functional groups.
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