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chemistry > organic chemistry > Flashcards

organic chemistry Flashcards

1
Q

what is crude oil and how can it be separated

A

-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

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2
Q

describe the fractional distillation of crude oil

A

-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

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3
Q

why is cracking needed

A

to break long carbon chain molecules into smaller more useful molecules

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4
Q

describe thermal cracking

A

-high temperature
-high pressure
-high proportions of alkanes and alkenes

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5
Q

describe catalytic cracking

A

-produces aromatic compounds
-lower temperature
-normal pressure
-zeolite catalyst

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6
Q

what are catalytic converters used for

A

-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

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7
Q

why are carbon particulates harmful

A

-they are small fragments of unburned hydrocarbons
-they can cause respiratory problems and contribute to global dimming

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8
Q

what is flue gas desulfurisation

A

-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

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9
Q

how do alkanes become halogenoalkanes

A

-they react with halogens in the presence of UV light

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10
Q

initiation step

A

Cl2 –> 2Cl*

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11
Q

propagation steps

A

Cl* + CH4 –> *CH3 + HCl
CH3 + Cl2 –> CH3Cl + Cl

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12
Q

termination step

A

*CH3 + *CH3 –> C2H6

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13
Q

common nucleophiles

A

CN:-
:NH3
:OH-

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14
Q

what is nucleophilic substitution for

A

forms alcohols from halogenoalkanes

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15
Q

what is elimination for

A

-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

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16
Q

how is ozone formed in the stratosphere

A

-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

17
Q

what are CFCs

A

-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

18
Q

show each step of ozone depletion

A

O3 + Cl* –> *ClO + O2
ClO + O3 –> 2O2 +Cl
overall: 2O3 –> 3O2

19
Q

how to minimise ozone depletion

A

developing CFC free solvents

20
Q

what are alkenes

A

-unsaturated hydrocarbons
-the double carbon bond has high electron density

21
Q

why is the 3o carbocation the major product

A

1o carbocations are very unstable.
2o carbocations are more stable.
3o carbocations are the most stable.
therefore, the 3o carbocation is the major product

22
Q

what are monomers and polymers

A

monomer - a single unit which joins together to form a larger molecule
polymer - a long chain molecule made up of 2 or more monomers

23
Q

describe addition polymers

A

-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

24
Q

reactivity of addition polymers

A

-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

25
Q

intermolecular forces between polyalkenes

A

-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

26
Q

what do plasticisers do

A

-makes a polymer more flexible - prevents chains getting as close
-e.g. it is added to polychloroethene which is water proof

27
Q

describe how bioethanol is produced

A

-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.

28
Q

compare fermentation and hydration when producing ethanol

A

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

29
Q

what are the conditions for fermentation and why

A

-between 30-40 degrees
-too hot and enzymes in yeast become denatured
-too low and rate of reaction will be too slow

30
Q

benefits of elimination

A

-alkenes produced can be used to produce addition polymers without using monomers derived from crude oil

31
Q

test for alcohols

A

-acidified potassium dichromate
-turns from orange to green if primary or secondary alcohols are present but remains orange if tertiary alcohols are present

32
Q

test for aldehydes

A

tollen’s reagent and warm gently
forms a silver mirror

33
Q

test for alkenes

A

turns bromine water from orange/brown to colourless

34
Q

test for carboxylic acids

A

react with sodium carbonate to produce carbon dioxide which turns limewater cloudy

chemistry (15 decks)

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