3.2 alkanes and halogenoalkanes

Question 1

what is fractional distillation?

Answer 1

separating crude oil into its fractions

Question 2

process of fractional distillation

Answer 2

crude oil vapourises and goes into bottom of column and rises
largest dont vapourise so run to bottom forming gooey reisdue
cooler as goes up
bp of alkanes increases as molecules get bigger as more vdw- each fraction condenses at diff temp and runs off
hydrocarbons w lowest bp dont condense and are draw off as gas at top

Question 3

order of fractions from lowest bp to highest and uses

Answer 3

gases- camping gas
petroleum- petrol
naphtha-petrochemicals
kerosene- jet fuel, petrochemicals,central heating fuel
diesel- diesel fuel, central heating fuel
mineral oil- lubricating oil
fuel oil- ships, power stations
wax, grease- candles, lubrication
bitumen-roofing, road surfacing

Question 4

what is cracking?

Answer 4

breaking long chain alkanes into smaller, more useful hydrocarbons
involves breaking c-c bond

Question 5

thermal cracking

Answer 5

high temp, high pressure
produces mainly alkenes which can be used to make polymers

Question 6

catalytic cracking
benefits
uses

Answer 6

zeolite catalyst (cuts cost as need lower temp and pressure and increases the rate), slight pressure, high temp
produces mainly alkanes needed for motor fuels

Question 7

problems with soot

Answer 7

breathing problems, build up in car engines so dont work well

Question 8

what is complete combustion?

Answer 8

burning alkanes with plenty of o2 to produce h2o and co2

Question 9

what is incomplete combustion?

Answer 9

burning alkenes with a lack of o2 to produce water and co and/or c

Question 10

problems with co

Answer 10

binds to haemoglobin so less space for o2 to be carried around body

Question 11

problems with soot

Answer 11

breathing problems, build up in exhausts so don’t work properly

Question 12

nitrogen oxides and how formed and problems

Answer 12

toxic and poisonous molecules with gen formula NOx
produced when high pressure and temp in engine
N2+O2 makes 2NO then 2NO+O2 makes 2NO2
can become nitric acid-acid rain -same process as SO2

Question 13

What do unburnt hydrocarbons react with and produce? what is the problem with this?

Answer 13

react with nitrogen oxides in air in presence of sunlight to produce ground level ozone which damages lungs, irritates eyes and causes respiratory probs

Question 14

Catalytic converter

Answer 14

made of platinum/palladium/rubidium and honeycomb structure (increases SA and makes less expensive)
remove pollutants from car exhausts

Question 15

reactions in catalytic converter

Answer 15

C3H8 + 5O2->3CO2 +4H2O (complete combustion)
2NO->N2+O2
2NO+2CO->N2+2CO2

Question 16

How is sulphur dioxide produced?
Problems?

Answer 16

fossil fuel may contain sulfur which reacts when burnt in engines to form SO2 which can dissolve in moisture in atmosphere to become sulfuric acid which causes acid rain

Question 17

Problems with acid rain

Answer 17

destroys trees, vegetation, statues, buildings, kills fish in lakes

Question 18

How can SO2 be removed from flue gases?

Answer 18

powdered calcium carbonate/oxide mixed with water to make alkaline slurry. mix this w flue gases and so2 reacts to form harmless calcium sulphate salt
CaO(s)+SO2(g)->CaSO3(s)

Question 19

Why can calcium oxide/ dioxide be used to remove SO2 from flue gases?

Answer 19

they are bases so neutralise the SO2

Question 20

what happens in free radical substitution and how does free radical substitution start?

Answer 20

Halogens react with alkanes to produce halogenoalkanes
UV light

Question 21

what is a free radical?

Answer 21

Particle with an unpaired electron. Formed when a covalent bond splits equally

Question 22

Steps of free radical substitution

Answer 22

Overall equation
Initiation
Propagation
Termination

Question 23

What is a CFC?

Answer 23

halogenoalkane where all H atoms have been replaced by Cl or F

Question 24

How is ozone formed?

Answer 24

O2 broken into free radicals
O2-> .O + .O
O2 + .O -> O3

Question 25

how is the ozone layer being destroyed by CFCs?

Answer 25

C-Cl bond breaks due to UV forming Cl radical (CCl3F-> .CCl2F + .Cl) which reacts with ozone to form O2 and ClO. ( Cl. + O3 -> O2 + ClO. then ClO. + O3 -> 2O2 + Cl.)
Cl. is regenerated so only need one to do lots of damage

Question 26

Overall equation for destruction of ozone

Answer 26

2O3->3O2

Question 27

what is a nucleophile?

Answer 27

Species with an atom with a lone pair of electrons which are attracted to an electron deficient carbon atom

Question 28

are halogenoalkanes polar or non-polar?

Answer 28

polar

Question 29

nucleophiles that react with halogenoalkanes

Answer 29

-:OH hydroxide alcohol
-:CN cyanide nitrile
:NH3 ammonia amine

Question 30

What happens in nucleophilic substitution?

Answer 30

nucleophile attacks polar molecule and replaces functional group
CH3CH2X + Nu- -> CH3CH2Nu + X-

Question 31

Summary of nucleophilic substitution

Answer 31

Between halogenoalkane and nucleophile
Nucleophile attacks d+ of C and breaks C-X bond
Bond formed bond broken
Balance charges at each stage

Question 32

Where do curly arrows start/ end

Answer 32

Start at electrons at bond/ lone pair and go to atoms

Question 33

What happens in an elimination reaction?

Answer 33

Small group of atoms breaks away from larger molecules and isn’t replaced

Question 34

How does elimination occur?

Answer 34

Warm halogenoalkane with hydroxide ions dissolved in ethanol
* OH- in ethanol and under reflux *
The OH acts as a base and removes H from halogenoalkane

Question 35

What is a Bronsted-Lowry base?

Answer 35

Base acts as a proton (H+ receptor)

Question 36

What happens if a halogenoalkane is in water and ethanol?

Answer 36

Elimination and substitution happen so there is a mixture of products (alcohols and alkenes)