3.3.2 Alkanes

Question 1

What are alkanes

Answer 1

Saturated hydrocarbons
Single covalent bonds
Only c and h
Name by longest section of the chain

Question 2

Properties of alkanes

Answer 2

Polarity - non polar small difference in electronegativity between the hydrogen and the carbon
Bp - longer the chain the higher the bp. As more electrons so stronger van der waals
Solubility - non polar so don’t dissolve in water

Question 3

Crude oil origins

Answer 3

Made form dead organic matter at the bottom of the ocean
Contains sulphur and sulphur oxides that when burnt creates acid rain

Question 4

Fractional distillation process

Answer 4

Hot crude oil is passed in#
All is heated and moves up the colomb as vapour
The colomb gets colder as it goes up
Teh fractions condense at ditrenrt levels and are piped of in fractions

Question 5

Fractional distillation order

Answer 5

Long - short
Bitumen,Fuel oil,gas oil,diesel, kerosine,naphtha,petrol, gasoline, gas

Question 6

Cracking why ?

Answer 6

Fractional distillation contains a higher fraction oof long chinese than needed
So cracked into smaller ones

Question 7

Thermal cracking

Answer 7

800-900 degrees
Up to 7000 kpa
Makes short alkanes and alkenes
Used for making polymers
Done with no air
Could lead to total decomposition

Question 8

Catalytic cracking

Answer 8

500 degrees
Just above atmospheric pressure
Silica and aluminium oxide zeolite catalyst
Makes branched alkanes,alkenes,aromatics,cycloalkanes
Used for moto fule

Question 9

Complete combustion

Answer 9

Lots of o2 needed
Makes co2 and h2o
Make sure that it is balanced

Question 10

Incomplete combustion

Answer 10

The carbon only undergoes partial oxidation so formes co
Unburnt carbon released as soot
Makes a mixture of carbon, carbon monoxide and h20
Co binds with haemoglobin in cells and stops them from carrying oxygen

Question 11

Environmental problems

Answer 11

When combustion takes place releases heat meaning high temperatures
Meaning the nitrogen and the oxygen in the air react
Foming nitrogen oxides eg nitrogen dioxide

As well as unburnt hydrocarbons
The unburnt hydrocarbons with light react with the the nitrogen oxides to produce photochemical smog

Question 12

Acid rain

Answer 12

So2 reacts with o to form so3 wich creates acid rain Contains dissolved co2 from atmosphere
An be created by so2 to make sulfuric acid (most common)
Or react with no2to create nitric acid

Question 13

Catalytic converters

Answer 13

Ceramic honeycomb coated in platinum or rhodium (Pt,Pd,Rh,Ir)
Harmful gases pass over and react to form less harmful

Question 14

Flue - gas desulfurization

Answer 14

Slurry of calcium oxide and water sprayed into the flue gas which reacts
Calcium oxide + water → calcium sulfate
Further oxidation gets you gypsum (ssalable product)
You can use calcium carbonate instead of calcium oxide to neutralise the gas)

Question 15

Free radical substitution ozone due to cfcs mechanisms

Answer 15

This is a chain reaction which means it causes depletion of the ozone

The ozone layer is in the stratosphere

cl. + o3 -> clo. + o2
clo. + o3 -> 2o2 + cl.

Question 16

Free radical substitution mechanism example

Answer 16

initiation
propagation - making hcl step 1
termination

Question 17

Free radical substitution steps

Answer 17

Initiation - uv provides the energy needed for homolytic fusion of the chorine (free radicals made)
Propagation (happens in 2 stages) - create a new different free radical and then recreate the first free radical
Termination - two free radicals join together and a variety of molecules are formed

Question 18

Free radicals

Answer 18

Very reactive species
Formed when a covalent bond breaks and one electron goes to each atom - homolytic fusion

Question 19

Important facts section

Answer 19

Nitrogen comes in a pair never nitrogen on there own
Think if fule is a solid
2CO + 2NO → CO2 +N2

Question 20

What catalysts are used in the catalytic converters

Answer 20

Platinum palladium - carbon monoxide → carbon dioxide
Platinum rhodium - oxides of nitrogen → n2 + o2

Question 21

What zeolite catalyst is used in catalytic cracking

Answer 21

Silicon dioxide, aluminium oxide

Question 22

How is water a greenhouse gas

Answer 22

More clouds that reflect the solar radiation

Question 23

How are haloalkanes formed

Answer 23

Halogen + alkane with UV to start the reaction

Question 24

Chloro fluoro carbons facts

Answer 24

low bp,c-cl has the lowest bond empathy which is why it breaks of first, cheap and non toxic, found in pollutants,aresols