3.2 Alkanes

Question 1

What is Fractional Distillation?

Answer 1

The process of separating crude oil into groups of hydrocarbon with a similar number of carbons

Question 2

What are the three stages of fractional distillation?

Answer 2

Evaporation ,Condensation, Collection

Question 3

What are the features of evaporation in fractional distillation?

Answer 3

Crude oil is heated until it evaporates
Crude oil vapour is put into a fractionating column

Question 4

What are the features of condensation in fractional distillation?

Answer 4

Temperature is higher at the bottom of the column
Long chains condense at bottom
Short chains are gasses and collect at the top

Question 5

What are Alkanes?

Answer 5

Saturated Hydrocarbons that can form cycloalkanes and functional group isomers

Question 6

What temperature is crude oil vaporised at?

Answer 6

350 °c

Question 7

How are alkane products used?

Answer 7

• Gasses- Can be used in gas stoves
• Kerosene- Used in jet fuel
• Bitumen- Used in roofing and tarmac

Question 8

What is the polarity of alkanes?

Answer 8

Almost non-polar (en of H + C are similar)
Only IMF are van der Waals

Question 9

What is the pattern with the boiling points of Alkanes?

Answer 9

Boiling point increases as chain length increases due to more vdW

5> carbons= gasses at room temp
5< x <18 carbons = liquid at room temp
18< = Solids (waxy feel)

Question 10

What is the solubility of Alkanes?

Answer 10

• Insoluble in water as water molecules are held to get her by H bonds
• Will mix with other non polar molecules

Question 11

What are the reactivity of alkanes?

Answer 11

Largely uncreative due to strong c-c and c-h
Will only react with halogens,under certain conditions
Will burn
(Lots of O2 = CO2 + H2O)
(Restricted supply of O2= CO / C

Question 12

What is cracking?

Answer 12

Breaking longer chain fractions into shorter ones

Question 13

What does cracking result in?

Answer 13

Shorter more useful chains (e.g petrol)
Some products are Alkanes which are more reactive

Question 14

Why are harsh conditions necessary for catalytic cracking?

Answer 14

Alkanes are mostly unreactive

Question 15

What are the conditions for thermal cracking?

Answer 15

High temp (700K - 1200K)
High pressure (up to 7000 Kpa)

Question 16

What happens in thermal cracking?

Answer 16

C-C bonds so one electron goes to each carbon atom
Initially two shorter chains are made ending with a C free radical
There isn’t enough hydrogen to make two Alkanes so one has a double bond and forms and alkene

Question 17

What is catalytic cracking?

Answer 17

Using a catalyst to crack alkanes resulting in lower temperatures and pressure

Question 18

What are the conditions catalytic cracking occur in?

Answer 18

720 K temperature
Just over 1 atm

Question 19

What is the catalyst called in catalytic cracking and what are the features?

Answer 19

• Uses a zeollic catalyst consisting of silicon dioxide + aluminium oxide
• Large Surface area
• Honeycomb structure
• Acidic

Question 20

When is catalytic cracking predominantly used?

Answer 20

To produce motor fuels
Or: Branched Alkanes,cycloalkanes and aromatic compounds

Question 21

How is catalytic cracking done in a lab?

Answer 21

Mineral wool is soaked in paraffin and put in a test tube aluminium oxide is added and gas is produced

Question 22

What is the definition of fuel?

Answer 22

Any substance that releases heat energy when burnt

Question 23

What is the definition of complete combustion?

Answer 23

Hydrocarbon burns completely in an excess of oxygen producing CO2 and H2O

Question 24

What is the definition of incomplete combustion?

Answer 24

Limited oxygen means hydrocarbon cannot fully combust producing CO and C

Question 25

What produces more energy per mole: Complete or incomplete combustion?

Answer 25

Complete combustion

Question 26

What forms carbon monoxide?

Answer 26

Incomplete combustion

Question 27

Why is carbon monoxide toxic?

Answer 27

Binds to Haemoglobin meaning less oxygen can be transported round body and causes suffocation

Question 28

How is sulphur dioxide formed?

Answer 28

Mostly through burning of coal in power stations

Question 29

How is SO2 dangerous to the environment?

Answer 29

Reacts with atmospheric water to form acid rain

SO2+1/2O2+H2O -> H2SO4

Question 30

How can SO2 be removed?

Answer 30

Flue gas desulfurisation

Question 31

How does flue gas desulfurisation work?

Answer 31

CaO or CaO3 is mixed with water to form a slurry
This is sprayed in chimneys
CaO+2H2O+SO2+1/2O2 —> CaSO4 ° 2H20

Question 32

What is the greenhouse effect?

Answer 32

UV radiation passes from sun to heat earths surface
Earth radiates infrared long wave radiation
The C=O bonds absorb infrared so the radiation cannot escape
Energy is transferred to other molecules through collisions
Surface temperature is rising

Question 33

What is a free radical?

Answer 33

Any species with an unpaired electron

Question 34

What is homolytic fission?

Answer 34

UV light causing covalent bonds to break into free radicals

Question 35

What is a haloalkane?

Answer 35

An alkanes where 1 or more H had been replaced by an alkane

Question 36

What are the three stages of the formation of haloalkanes?

Answer 36

Initiation,propagation,termination

Question 37

What does propagation form?

Answer 37

A chain reaction

Question 38

What is O3 and what does it do?

Answer 38

Ozone
Absorbs harmful UV radiation from the sun

Question 39

What is damaging about CFC’s?

Answer 39

They destroy the ozone layer