Alcohol and carboxylic acids Flashcards
Alcohols
Homologous series containing - OH as functional group
Primary alcohol
OH join to a carbon and 2 other hydrogens
Secondary alcohol
O H Group is joined to a 2 alkyl groups and hydrogen
Tertiary alcohol
Join to three carbons and no hydrogens
Hydration of ethene
Obtained by cracking hydrocarbons produced from petroleum, react with steam to produce ethanol
CH2=CH2(g) + H2O(g) —> CH3CH2OH (g)
Le Chateliars principle
States that if a system at equilibrium is subjected to a change, the equilibrium tends to shift so as to minimise the effect of the change
Temperature in hydration of ethene
Since the forward reaction is exothermic, a high yield will be favoured by a low temperature., however, gives a slow rate of reaction: 300 degrees is a comprise temperature
Pressure and hydration of ethene
In the reaction, two moles of gas reactor produce 1 mole of gas. A high yield is therefore favoured by a high pressure
high pressure also increases the rates of reaction
60-70 atm
Reasons high pressure isn’t used
if pressure is too high more powerful pumps and stronger pipes are needed and this increases costs
At high pressure ethene polynerisis into polyethene and this wastes ethene and clogs up the plant
catalyst in hydration of ethene
Catalyst does not affect the yield but it does increase the rate in which ethene and steam react to produce the equilibrium concentration of ethanol
Catalyst of phosphoric acid coated onto a inert solid
Inert solid
Doesn’t react with anything so the solid won’t react and change the reaction
Fermentation of etheme
Enzyme catalysted reaction that converts sugars to ethanol
eg glucose: C6H12O6 —> 2C2H5OH + 2CO2
Fractional distillation needed in fermentation
Carbon dioxide escapes as a gas but ethanol has to be separated from the remaining liquid mixture. Temperature of ethanol is seventy eight degrees and therefore to separate it from an aqueous mixture fractional distillation is needed
Biofuel
Fuel that has been produced using a biological source
Advantages of biofuel - renewable
Fossil fuels are non-renewable and will eventually run out. Can be grown each year and biofuels can also be produced using waste material from animals
Advantages of biofuels - greenhouse gases
Production of carbon dioxide is reduced
Carbon dioxide is taken in by plants when they are grown and used for photosynthesis to produce sugars
Carbon dioxide is produced in one process but removed in another so use of biofuels is carbon neutral
Carbon neutral
Process where there is no net transfer of carbon dioxide to or from atmosphere
Advantages of biofuels - economic and political security
Countries that are able to grow crops like sugar cane and create own biofuels do not need to use fossil fuels
Countries producing biofuels are less affected by changes in fossil fuel prices and changes in availability
Disadvantages of biofuels - land use
land Used to produce plants for biofuels cannot be used to produce food, there is also pressure to destroy environmentally significant areas like forests to create land for biofuel production
Disadvantages of biofuels- use of resources
Growing crop suitable for biofuels in these large quantities of water and fertilisers. use of Water can strain local resources and use of large quantities of fertilisers to grow the same crop year after year can cause water pollution
Disadvantages of biofuels - carbon neutrality
When the fuel needed to build and run the factories for biofuel production, to transport raw materials and finished products is considered
It can be argued that the use of such fuels is not carbon neutral
Oxidation of alcohols
Acidified potassium dichromate can be used to oxidise many alcohols
The dichromate will only behave satisfaction as an oxidising agent to the presence of H+
Carried out by heating alcohol with a mixture of aqueous potassium dichromate and sulfuric acid
Oxidation of primary alcohols
Two stages
Eg. Ethanol + [O] –> Ethanal + H2O
Stage1:
Two hydrogen atoms are lost - one from the alcohol O H and one from the adjacent carbon creating carbon to oxygen double bond
Stage 2:
Ethanal + [O] –> Ethanoic acid
Oxygen is added to the aldehyde
Oxidation of secondary alcohols
Eg. Propan-2-ol
One stage,
Propan-2-ol + [O] –> propanone + H2O
Ketone
Oxidation of tertiary alcohols
Eg. 2- methylpropa-2-ol
There is no hydrogen on an adjacent carbon that can be lost so no reaction takes place
Colour change of acidified potassium dichromate
Changes from orange to green
Test for primary and secondary alcohol since they will give positive test results for tertiary alcohols will not
Structure of carboxylic acids
R-C=O
-O-H
Acidic because they release H ions when added to water
weak acid so when it dissolves in water only a small percentage of H ions are formed
Reactions of carboxylic acids- as an acid reacts to bases
Both soluble bases like alkali’s and solid bases like metal oxides neutralised carboxylic acids
Acid + base = salt + water
( alkali NaOH) All reagents and products are colourless and solid boiling water so no visible change occurs
( CuO) when warm the black solid copper oxide dissolves the form blue solution of as salt
Reactions of carboxylic acids carbonates and hydrocarbonates
both react in similar ways
Acid + carbonate = salt + CO2 + H2O
Co2 is always produced, therefore an effveressence is seen and a gas can be shown testing w limewater
Reactions of carboxylic acids Esterification
react w alcohols
Carboxylic acid + alcohol –> ester + water
Reaction is catalysed by presence of concentrated sulfuric acid
esther produced has charactistic sweet fruity odor
Practical activity - ester
Carboxylic acid alcohol and concentrated sulfuric acid are heated together in a flask producing equilibrium mixture of Esther with some carboxylic and alcohol. Esther removed by distillation
Dehydration of alcohol
Dehydrated to form alkanes + H2O
Concentrated sulfuric acid or heated aluminium oxide commonly used
Reaction is the elimination since double bond is produced by removal of O H from one carbon and one H from adjacent carbon atom
