organic chemistry Flashcards
what is crude oil and how can it be separated
-a mixture of different hydrocarbons
-can be separated by fractional distillation as the different chain lengths of the molecules mean they have different boiling points
describe the fractional distillation of crude oil
-the mixture is vapourised before entering the vapourising column
-the vapours rise, cool and condense according
-the products are separated and removed for different uses
why is cracking needed
to break long carbon chain molecules into smaller more useful molecules
describe thermal cracking
-high temperature
-high pressure
-high proportions of alkanes and alkenes
describe catalytic cracking
-produces aromatic compounds
-lower temperature
-normal pressure
-zeolite catalyst
what are catalytic converters used for
-internal combustion engines may produce oxides of nitrogen (can cause acid rain) and carbon monoxide (toxic gas)
-catalytic converters use a rhodium catalyst to convert these harmful products into more stable products such as CO2 or H2O
why are carbon particulates harmful
-they are small fragments of unburned hydrocarbons
-they can cause respiratory problems and contribute to global dimming
what is flue gas desulfurisation
-the combustion of hydrocarbons that contain sulfur forms sulfur dioxide which causes air pollution and acid rain
-calcium oxide is used to neutralise the gas in flue gas desulfurisation
how do alkanes become halogenoalkanes
-they react with halogens in the presence of UV light
initiation step
Cl2 –> 2Cl*
propagation steps
Cl* + CH4 –> *CH3 + HCl
CH3 + Cl2 –> CH3Cl + Cl
termination step
*CH3 + *CH3 –> C2H6
common nucleophiles
CN:-
:NH3
:OH-
what is nucleophilic substitution for
forms alcohols from halogenoalkanes
what is elimination for
-when a halogenoalkane is heated to a high temperature under alcoholic conditions.
-the nucleophile acts as a base and accepts a proton
-an alkene is formed
how is ozone formed in the stratosphere
-ordinary stable oxygen is split into 2 oxygen atoms by UV radiation
O2 –> 2O
-a free oxygen atom combines with the an oxygen molecule to form ozone
O + O2 –> O3
-when ozone absorbs UV radiation, it will decompose into oxygen molecules
O3 –> O2 + O
what are CFCs
-CFCs are compounds that contain carbon, fluorine and chlorine
-they diffuse into the stratosphere where UV light provides energy to break the C-Cl bond and form Cl* radicals
-these radicals catalyse the depletion of ozone
show each step of ozone depletion
O3 + Cl* –> *ClO + O2
ClO + O3 –> 2O2 +Cl
overall: 2O3 –> 3O2
how to minimise ozone depletion
developing CFC free solvents
what are alkenes
-unsaturated hydrocarbons
-the double carbon bond has high electron density
why is the 3o carbocation the major product
1o carbocations are very unstable.
2o carbocations are more stable.
3o carbocations are the most stable.
therefore, the 3o carbocation is the major product
what are monomers and polymers
monomer - a single unit which joins together to form a larger molecule
polymer - a long chain molecule made up of 2 or more monomers
describe addition polymers
-made from alkenes
-during polymerisation, the double bond opens up and the monomers join together to form one long saturated chain
-the polymer is the only product
reactivity of addition polymers
-non-polar so insoluble in water
-generally very unreactive
-takes a long time to break down (non-biodegradable)
-therefore used as inert materials e.g. insulators/packaging/containers
intermolecular forces between polyalkenes
-only VDW forces
-longer chains = more VDW as there are more e-s.
-the closer the chains can pack together (smaller groups), the stronger the VDW
what do plasticisers do
-makes a polymer more flexible - prevents chains getting as close
-e.g. it is added to polychloroethene which is water proof
describe how bioethanol is produced
-sugar cane is fermented to produce glucose
-the glucose is fermented with yeast to form ethanol
photosynthesis of sugar cane:
6CO2 + 6H2O –> C6H12O6 + 6O2
the production of ethanol:
C6H12O6 –> 2C2H5OH +2CO2
combustion of ethanol:
2C2H5OH + 6O2 –> 4CO2 + 6H2O
-ethanol produced industrially by fermentation is separated by fractional distillation and can then be used as a biofuel.
compare fermentation and hydration when producing ethanol
fermentation:
-continuous process so it is fast
-no waste products - 100% atom economy
-non-renewable resource
-lots of energy used due to hi
hydration:
-cheaper as it can be carried out at a lower temperature
-must be fermented in batches so it is slower and has a lower atom economy
-considered carbon neutral
-however, still has environmental issues e.g. growing crops for biofuel takes up large areas of land which can greatly impact biodiversity and the transport of bioethanol produces carbon emissions
what are the conditions for fermentation and why
-between 30-40 degrees
-too hot and enzymes in yeast become denatured
-too low and rate of reaction will be too slow
benefits of elimination
-alkenes produced can be used to produce addition polymers without using monomers derived from crude oil
test for alcohols
-acidified potassium dichromate
-turns from orange to green if primary or secondary alcohols are present but remains orange if tertiary alcohols are present
test for aldehydes
tollen’s reagent and warm gently
forms a silver mirror
test for alkenes
turns bromine water from orange/brown to colourless
test for carboxylic acids
react with sodium carbonate to produce carbon dioxide which turns limewater cloudy
