C6.2 - Organic chemistry Flashcards
what is crude oil?
- fossil fuel from remains of marine organisms that lived millions of years
how is crude oil formed?
chemical reactions + action of heat and pressure turned remains of dead marine organisms into crude oil
Methane formula
CH4
Ethane formula
C2H6
Propane formula
C3H8
Butane formula
C4H10
what does crude oil contain?
mixture of hydrocarbons - mostly alkanes
what are hydrocrabons?
substances made of only hydrogen and carbon atoms
what happens when alkanes get bigger?
bpt increases - TMT you can separate different molecules using fractional distillation
what is an alkane?
a hydrocarbon
what is the general formula for an alkane?
CnH2n+2
What is the Ethane displayed formula
H H | | H - C - C - H | | H H
what is the ethane structural formula?
CH3CH3
What is the ethane skeletal formula?
/
What is the Propane displayed formula
H H H | | | H - C - C - C - H | | | H H H
What is the structural formula of Propane?
CH3CH2CH3
What is the skeletal formula for propane?
/\
What is the Butane displayed formula?
H H H H | | | | H - C - C - C - C - H | | | | H H H H
What is the structural formula for Butane?
CH3CH2CH2CH3
What is the skeletal formula for butane?
/\/
properties of alkanes
- saturated molecules (as only contain single covalent bonds)
- unreactive (as only contain strong single covalent bonds)
- Bpt and viscosity increases as you increase the chain length
- flammability + volatility decrease as you increase chain length
- form homologous series - as have similar chem properties + trend in physical properties as you change the chain by -CH2
when do alkanes undergo combustion reactions?
when they react with oxygen in the air and burn
complete combustion equation
Alkane + oxygen –> carbon dioxide + water
CH4 + 2O2 –> CO2 + 2H2O
what is complete combustion?
when lots O2 available, reaction is complete & produces CO2 and water
- E.g. Bunsen burner with an open air-hole
incomplete combustion reaction
Alkane + oxygen –> Carbon dioxide + water + carbon monoxide + soot
4CH4 + 6O2 –> CO2 + 8H2O + 2CO + C
What is incomplete combustion?
when not enough O2 available - e.g. Bunsen burner with closed air-hole (safety flame)
how do you separate alkanes from crude oil?
fractional distillation - bpt increases as chain length increases - TIB the longer the chain the stronger the intermolecular forces
How does fractional distillation work?
- crude oil piped into fractionating column
- bottom of column has highest temp
- smaller molecules have lowest bpt so evaporate 1st rising to top of column - continue to rise until it becomes cool enough to condense back into liquid (when they are collected)
what are alkanes used as?
fuels - basic form of a hydrocarbon found in crude oil
what is cracking?
turning longer alkane chains into shorter ones (shorter chains are more useful)
example formula of cracking
decane –> octane + ethene
C10H22–>C8H18 + C2H4
Industrial conditions for cracking
high temps required (often means heating samples to 600-700°C in presence of hot catalyst of alumina/silica)
- under these conditions, strong covalent bonds between atoms can break
what does cracking produce?
shorter alkane chains and alkenes
why are alkenes useful?
helpful in production of polymers - e.g. plastics
what are alkenes produced from?
by-product of cracking
alkene general formula
CnH2n
Alkene characteristics
- form homologous series - TIB of common features
- unsaturated molecules as contain double bond between 2 carbon atoms