3.2 alkanes and halogenoalkanes Flashcards
what is fractional distillation?
separating crude oil into its fractions
process of fractional distillation
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
order of fractions from lowest bp to highest and uses
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
what is cracking?
breaking long chain alkanes into smaller, more useful hydrocarbons
involves breaking c-c bond
thermal cracking conditions and products
high temp, high pressure
produces mainly alkenes which can be used to make polymers
catalytic cracking
benefits
uses
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
problems with soot
breathing problems, build up in car engines so dont work well
what is complete combustion?
burning alkanes with plenty of o2 to produce h2o and co2
what is incomplete combustion?
burning alkenes with a lack of o2 to produce water and co and/or c
problems with co
binds to haemoglobin so less space for o2 to be carried around body
problems with soot
breathing problems, build up in exhausts so don’t work properly
nitrogen oxides and how formed and problems
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
What do unburnt hydrocarbons react with and produce? what is the problem with this?
react with nitrogen oxides in air in presence of sunlight to produce ground level ozone which damages lungs, irritates eyes and causes respiratory probs
Catalytic converter
made of platinum/palladium/rubidium and honeycomb structure (increases SA and makes less expensive)
remove pollutants from car exhausts
reactions in catalytic converter
C3H8 + 5O2->3CO2 +4H2O (complete combustion)
2NO->N2+O2
2NO+2CO->N2+2CO2
How is sulphur dioxide produced?
Problems?
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
Problems with acid rain
destroys trees, vegetation, statues, buildings, kills fish in lakes
How can SO2 be removed from flue gases?
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)
Why can calcium oxide/ dioxide be used to remove SO2 from flue gases?
they are bases so neutralise the SO2
what happens in free radical substitution and how does free radical substitution start?
Halogens react with alkanes to produce halogenoalkanes
UV light
what is a free radical?
Particle with an unpaired electron. Formed when a covalent bond splits equally
Steps of free radical substitution
Overall equation
Initiation
Propagation
Termination
What is a CFC?
halogenoalkane where all H atoms have been replaced by Cl or F
How is ozone formed?
O2-> .O + .O
O2 + .O -> O3
how is the ozone layer being destroyed by CFCs?
CCl3F-> .CCl2F + .Cl
Cl. + O3 -> O2 + ClO. then ClO. + O3 -> 2O2 + Cl.
Cl. is regenerated so only need one to do lots of damage
Overall equation for destruction of ozone
2O3->3O2
what is a nucleophile?
Species with an atom with a lone pair of electrons which are attracted to an electron deficient carbon atom
are halogenoalkanes polar or non-polar?
polar
nucleophiles that react with halogenoalkanes
-:OH hydroxide alcohol
-:CN cyanide nitrile
:NH3 ammonia amine
What happens in nucleophilic substitution?
nucleophile attacks polar molecule and replaces functional group
CH3CH2X + Nu- -> CH3CH2Nu + X-
Summary of nucleophilic substitution
Between halogenoalkane and nucleophile
Nucleophile attacks d+ of C and breaks C-X bond
Bond formed bond broken
Balance charges at each stage
Where do curly arrows start/ end
Start at electrons at bond/ lone pair and go to atoms
What happens in an elimination reaction?
Small group of atoms breaks away from larger molecules and isn’t replaced
How does elimination occur (conditions)?
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
What is a Bronsted-Lowry base?
Base acts as a proton (H+ receptor)
What happens if a halogenoalkane is in water and ethanol?
Elimination and substitution happen so there is a mixture of products (alcohols and alkenes)
