Define saturated hydrocarbons
A molecule made only of carbon and hydrogen with only single bonds
Define unsaturated hydrocarbons
A molecule made only of carbon and hydrogen that contains a double bond
List the features of a homologous series
- Similar chemical properties
Because they have same functional group
-Same general formula
-Trend in physical properties
How do you separate a mixture of alkanes? (e.g. crude oil)
Fractional distillation
The larger the hydrcarbon…
The higher the boiling point and the less volatile
Define volatile
Easily turned into a vapour, low bpt
Pollutant: Carbon Dioxide
Source: complete combustion of fuel
Problem: Greenhouse gas—-> global warming
Solution: CCS- carbon capture and storage, used in extinguishers
Pollutant: Carbon monoxide
Source: incomplete combustion of fuel
Problem: Toxic, replaces oxygen and binds to haemoglobin, less respiration
Solution: catalytic converters
What is the equation used in catalytic converters?
CO + NO —–> CO₂ + 1/2 N₂
What catalyst is used and why is it spread in a ‘honeycomb support’?
Paladium, to maximise SA
Pollutant : Carbon
Source: incomplete combustion of fuel
Problem: medical particulates lead to lung cancer/ environmental global dimming
Solution: Filter, solids get trapped
Pollutant : SO2
Source: Sulfur impurities in fuel burning
Problem: Acid rain, lowers pH of ocean, corrodes limestone
Solution: neutralise with lime/ slaked lime (CaO)
Pollutant : NOx
Source: N from air, very high temp causes spark
Problem: Acid rain, lowers pH of ocean etc.
Solution: Catalytic converter
What mechanism is involved with the reaction of alkanes?
Free radical substitution
Stage 1 of free radical sub.
Initiation
Cl₂ ———–> [UV light] 2Cl•
Define free radical
A highly reactive species with an unpaired electron
Stage 2 of free radical sub.
Propagation
a) Cl• + CH₄ ———–>•CH₃ +HCl
b) •CH₃+ Cl₂ ———-> CH₃Cl + Cl•
Stage 3 of free radical sub.
Cl • + •CH₃ ———–> CH₃Cl + Cl •
Thermal cracking
-free radical sub.
Conditions: High temp, 400-900 deg.C and high pressure (70atm)
Equation: C₈H₁₈ ——-> C₆H₁₄ + C₂H₄
Products: High % of alkenes for polymers
Catalytic cracking
-carbocation
Conditions : High temp- 450 deg.C, Low press- ~>1 atm, Catalyst zeolite
Products: Motor fuels, branched alkanes
Why do we do cracking?
- Supply and demand
- high demand for small molecules
- high supply of big molecules
- crack to make smaller from bigger
Smaller molecules are…
- less volatile
- easier to ignite
Alkenes test
Orange bromine water goes colourless
Are alkenes reactive and why?
They are due to double bond that has a region of high electron density
What type of reactions do alkenes do?
Electrophilic addition
Where do the curly arrows go in alkene mechanisms?
From double bond to d+ atom, from single bond to Cl or Br
From lone pair on halogen to positive C
Where is thte major product formed with unsymmetrical alkenes?
The more stable carbocation
Order of stability and why?
Primary < Secondary < Tertiary
This is due to electron releasing effect of alkyl groups
Alkenes + sulphuric acid, conditions?
Cold concentrated sulphuric acid
central S, H–O recieves pair of e- from double bond
(Sulphuric acid reformed at end so it acts as a catalyst)
How do you draw H₂SO₄?
Central S, 2OH, and 2 =OS