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1
Q

fractional distillation of alkanes

A

Oil is pre-heated
* then passed into column. * The fractions condense at different heights
* The temperature of column decreases upwards
* The separation depends on boiling point. * Boiling point depends on size of molecules. * The larger the molecule the larger the van der waals forces
* Similar molecules (size, bp, mass) condense together * Small molecules condense at the top at lower temperatures

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2
Q

fractional distillation in the lab

A
  • Heat the flask, with a Bunsen burner or electric
    mantle
  • This causes vapours of all the components in the
    mixture to be produced. * Vapours pass up the fractionating column. * The vapour of the substance with the lower boiling
    point reaches the top of the fractionating column
    first. * The thermometer should be at or below the boiling
    point of the most volatile substance. * The vapours with higher boiling points condense
    back into the flask. * Only the most volatile vapour passes into the
    condenser. * The condenser cools the vapours and condenses to
    a liquid and is collected.
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3
Q

what is cracking

A

conversion of large hydrocarbons to smaller hydrocarbon molecules by breakage of C-C bonds

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4
Q

economic reasons for cracking

A

The petroleum fractions with shorter C chains are in more demand than larger fractions.
The products of cracking are more valuable than the starting
materials

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5
Q

two types of cracking

A

thermal and catalytic

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6
Q

thermal cracking conditions

A

High pressure (7000 kPa)
High temperature (400°C to 900°C)

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7
Q

thermal cracking conditions

A

produces mostly alkenes e.g. ethene used
for making polymers and ethanol
sometimes produces hydrogen used in the
Haber Process and in margarine manufacture.

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8
Q

catalytic cracking conditions

A

Slight or moderate pressure
High temperature (450°C)
Zeolite catalyst

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9
Q

products oc catalytic cracking

A

Produces branched and cyclic
alkanes and aromatic hydrocarbons
Used for making motor fuels
Cheaper than thermal cracking because it saves
energy as lower temperatures and pressures are used

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10
Q

so2

A

SO2 will dissolve in atmospheric water and can produce acid rain
SO2 can be removed from the waste gases from furnaces by flue gas desulfurisation
basic calcium oxide which reacts with the acidic
sulfur dioxide in a neutralisation

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11
Q

no

A

Nitrogen oxides form from the reaction between N2 and O2
inside the car engine.
The high temperature and spark in the engine provides sufficient energy to break strong N2 bond

NO is toxic and can form acidic gas NO2

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12
Q

catalytic converters

A

These remove CO, NOx and unburned hydrocarbons (e.g. octane, C8H18)
from the exhaust gases, turning them into ‘harmless’ CO2
, N2 and H2O.

Converters have a ceramic
honeycomb coated with a thin
layer of catalyst metals
platinum, palladium, rhodium– to give a large surface area

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13
Q

greenhouse effect

A

UV wavelength radiation passes through the atmosphere to the Earth’s surface and heats up Earth’s surface.
The Earth radiates out infrared long wavelength radiation.
The C=O Bonds in CO2 absorb infrared radiation so the IR radiation does not escape from the atmosphere.
This energy is transferred to other molecules in the atmosphere by collisions so the atmosphere is warmed.

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14
Q

why alkanes do not react with many reagents

A

This is because the C-C bond
and the C-H bond are relatively
strong

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15
Q

uv light

A

The UV light supplies the energy to break the Cl-Cl bond. It is
broken in preference to the others because it is the weakest.

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16
Q

free radical

A

A free radical is a reactive species which
possess an unpaired electron

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17
Q

Primary halogenoalkane

A

One carbon attached to the
carbon atom adjoining the
halogen

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18
Q

Secondary halogenoalkane

A

Two carbons attached to the
carbon atom adjoining the
halogen

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19
Q

Tertiary halogenoalkane

A

Three carbons attached to the
carbon atom adjoining the
halogen

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20
Q

Halogenoalkanes undergo either

A

substitution or elimination

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21
Q

Nucleophile

A

electron pair donator e.g. :OH-, :NH3
, CN

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22
Q

Aqueous silver nitrate

A

added to a halogenoalkane
halide leaving group combines with a silver ion to form a
silver halide precipitate
The quicker the precipitate is formed, the faster the substitution
reaction and the more reactive the halogenoalkane
AgI
(s) - yellow precipitate
AgBr(s) – cream precipitate
AgCl
(s) – white precipitate

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22
Q

Nucleophilic substitution with aqueous hydroxide ions

A

Change in functional group: halogenoalkane 
alcohol
Reagent: potassium (or sodium) hydroxide
Conditions: In aqueous solution; Heat under reflux
Mechanism: Nucleophilic Substitution
Type of reagent: Nucleophile, OH-

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23
Q

Nucleophilic substitution with cyanide ions

A

Change in functional group: halogenoalkane 
nitrile
Reagent: KCN dissolved in ethanol/water mixture
Conditions: Heating under reflux
Mechanism: Nucleophilic Substitution
Type of reagent: Nucleophile, :CN-

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24
24
Nucleophilic substitution with ammonia
Change in functional group: halogenoalkane  amine Reagent: NH3 dissolved in ethanol Conditions: Heating under pressure (in a sealed tube) Mechanism: Nucleophilic substitution Type of reagent: Nucleophile, :NH3
25
Elimination with alcoholic hydroxide ions
Change in functional group: halogenoalkane  alkene Reagents: Potassium (or sodium) hydroxide Conditions: In ethanol ; heat Mechanism: Elimination Type of reagent: Base, OH Aqueous: substitution Alcoholic: elimination Primary tends towards substitution Tertiary tends towards elimination
26
Uses of Halogenoalkanes
Chloroalkanes and chlorofluoroalkanes can be used as solvents. Halogenoalkanes have also been used as refrigerants, pesticides and aerosol propellants CH3CCl3 was used as the solvent in dry cleaning. Many of these uses have now been stopped due to the toxicity of halogenoalkanes and also their detrimental effect on the atmosphere.
27
(CFC’s)
caused a hole to form in the ozone
28
e chlorine free radical
catalyse the decomposition of ozone, due to these reactions, because they are regenerated. (They provide an alternative route with a lower activation energy) These reactions contributed to the formation of a hole in the ozone layer.
29
CH2FCF3 are now used for refrigerators and air-conditioners why
These are safer as they do not contain the C-Cl bond. The C-F bond is stronger than the C-Cl bond and is not affected by UV
30
alkenes genral fromula
CnH2n carbon- carbon double bond
31
The arrangement of bonds around the >C=C< i
planar and has the bond angle 120o
32
C=C double covalent bond consists of
one sigma (σ) bond and one pi (π) bond. π bonds are exposed and have high electron density. They are therefore vulnerable to attack by species which ‘like’ electrons: the
33
Stereoisomerism
Stereoisomers have the same structural formulae but have a different spatial arrangement of atoms
34
how ez isomers raise
There is restricted rotation around the C=C double bond. (b) There are two different groups/atoms attached both ends of the double
35
Electrophile
an electron pair accepto
36
Reaction of bromine with alkenes
Change in functional group: alkene  dihalogenoalkane Reagent: Bromine Conditions: Room temperature (not in UV light) Mechanism: Electrophilic addition Type of reagent: Electrophile, Br+
37
Reaction of hydrogen bromide with alkenes
Change in functional group: alkenehalogenoalkane Reagent: HCl or HBr Conditions: Room temperature Mechanism: Electrophilic addition Type of reagent: Electrophile, H+
37
why hbr is polar
HBr is a polar molecule because Br is more electronegative than H. The H δ + is attracted to the electron
38
‘Markownikoff’s Rule’
In most cases, bromine will be added to the carbon with the fewest hydrogens attached to it If the alkene is unsymmetrical, addition of hydrogen bromide can lead to two isomeric products.
39
Reaction of sulfuric acid with alkenes
Stage 1 Change in functional group alkene  alkyl hydrogensulfate Reagents: concentrated H2SO4 Conditions: room temperature Mechanism: Electrophilic addition Type of reagent: Electrophile, H2SO
40
Direct industrial hydration of alkenes to form alcohols
Essential conditions High temperature 300 to 600°C High pressure 70 atm Catalyst: concentrated H3PO4
41
poly chlorophyll ethene
water proof used make uPVC window frame coverings and guttering If a plasticiser is added the intermolecular forces are weakened which allows the chains to move more easily, resulting in more flexibility in the polymer. In this form PVC is used to make insulation on electrical wires, and waterproof clothing.
42
alkene reagent
Bromine water
43
aldehyde reagent
Tollens’ reagent Silver mirror formed Fehling’s solution Blue solution to red precipitate
44
cabroxylic acid reagents
Sodium carbonate Effervescence of CO2 evolved
45
primary secondary aldehydes
sod dichromate and sulphuric acid orange to green
46
chloroalkane reagents
warm with silver nitrate slow formations of white ppt of agcl
47
carboxylic acid
d can be tested by addition of sodium carbonate. It will fizz and produce carbon dioxide
48
primary alcohol
Primary alcohols are alcohols where 1 carbon is attached to the carbon adjoining the oxygen.
49
secondary alcohol
Secondary alcohols are alcohols where 2 carbon are attached to the carbon adjoining the oxygen
50
tertiary alcohol
Tertiary alcohols are alcohols where 3 carbon are attached to the carbon adjoining the oxygen
51
Partial Oxidation of Primary Alcohols
Reaction: primary alcohol  aldehyde Reagent: potassium dichromate (VI) solution and dilute sulfuric acid. Conditions: (use a limited amount of dichromate) warm gently and distil out the aldehyde as it forms:
52
Full Oxidation of Primary Alcohols
Reaction: primary alcohol  carboxylic acid Reagent: potassium dichromate(VI) solution and dilute sulfuric acid Conditions: use an excess of dichromate, and heat under reflux: (distil off product after the reaction has finished)
53
Oxidation of Secondary Alcohols
Reaction: secondary alcohol  ketone Reagent: potassium dichromate(VI) solution and dilute sulfuric acid. Conditions: heat under reflux
54
Reaction of Alcohols with Dehydrating Agents
Reaction: Alcohol  Alkene Reagents: Concentrated sulfuric or phosphoric acids Conditions: warm (under reflux) Role of reagent: dehydrating agent/catalyst Type of reaction: acid catalysed elimination
55
fermentation
glucose  ethanol + carbon dioxide C6H12O6  2 CH3CH2OH + 2 CO2 The conditions needed are: *Yeast *No air *temperatures 30 –40oC The optimum temperature for fermentation is around 38oC At lower temperatures the reaction is too slow. At higher temperatures the yeast dies and the enzymes denature. Fermentation is done in an absence of air because the presence of air can cause extra reactions to occur. It oxidises the ethanol produced to ethanoic acid (vinegar). Advantages *sugar is a renewable resource *production uses low level technology / cheap equipment Disadvantages *batch process which is slow and gives high production costs *ethanol made is not pure and needs purifying by fractional distillation *depletes land used for growing food crops
56
ethene
high temperature 300 °C high pressure 70 atm strong acidic catalyst of conc Advantages: *faster reaction *purer product *continuous process (which means cheaper manpower) Disadvantages: *high technology equipment needed (expensive initial costs) *ethene is non-renewable resource (will become more expensive when raw materials run out) *high energy costs for pumping to produce high pressures
57
Ethanol as biofuel
A biofuel is a fuel produced from plants d from fermentation e any carbon dioxide given off when the biofuel is burnt would have been extracted from the air by photosynthesis when the plant grew. There would be no net CO2 emission into the atmosphere
58
fingerprint".
This part of the spectrum is unique for every compound
59
Aldehydes can be oxidised to
carboxylic acids, but ketones cannot be oxidised.
60
Oxidation of aldehydes
Reaction: aldehydecarboxylic acid Reagent: potassium dichromate (VI) solution and dilute sulfuric acid. Conditions: heat under reflux

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