3.3.2 Alkanes

How does fractional distillation work

By separating crude oil into different fractions as different chain lengths of molecules have different boiling points

what is crude oil

a mixture of hydrocarbons

steps of fractional distillation of crude oil

the crude oil is vaporised, passed through the fractionating column which has a temperature gradient - hot at bottom, cooler at top. vapour rises as it cools. vapour condenses at different fractions as the different molecules have different boiling points. the larger the molecule, the higher the BP so the lower down the column it condenses. fractions are then collected

graduation of physical properties of small to large hydrocarbons

low to high BP, light to dark in colour, easy to hard to light, runny to viscous.

thermal cracking conditions and products

700 degrees C and 7000 kPa. breaks C-C bonds to form smaller alkanes and alkenes

Catalytic cracking conditions and products

zeolite catalyst, 450 degrees C and normal pressure. produced aromatic and branched alkanes.

products of complete combustion

CO2 (g) and H2O (l)

products of incomplete combustion

CO (g) and H2O (l) or C (s) and H2O (l)

how do catalytic converters work

remove CO, NOx and unburned hydrocarbons by using a rhodium catalyst to convert toxic products into CO2, H2O and N2. In a honeycomb shape for maximised surface area for a fast reaction

Reaction of NO and CO

2NO + 2CO -> N2 + 2CO2

what is the problem with carbon particulates and how are they formed

they are formed from incomplete combustion in factories and cause respiratory problems as they pollute the air

How is SO2 produced

sulfur impurities are found in petrol fractions which produce SO2 when burnt

problems with SO2 being produced

SO2 reacts with rainwater to produce sulfuric acid, H2SO4. it causes acidification of water and acid rain

what is used to desulfurise the flue gases

calcium oxide is used to form calcium sulfate. CaO + SO2 -> CaSO3

why do some molecules absorb IR

polar molecules absorb IR which makes the covalent bonds vibrate

example of polar molecule

H2O

What is needed for the chlorination of alkanes and why

presence of UV light as alkanes are very unreactive

what type of mechanism is chlorination of alkanes

free radical substitution