ks4: useful products from organic sources organic chemistry
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KS4: Useful Products from Organic Sources ORGANIC CHEMISTRY. Crude Oil. Crude oil is a mixture ; it contains hundreds of different compounds, some small and some extremely large. Nearly all these compounds contain carbon and hydrogen only and are called hydrocarbons. - PowerPoint PPT PresentationTRANSCRIPT
© Boardworks Ltd 2001
KS4: Useful Products from Organic Sources
ORGANIC CHEMISTRY
© Boardworks Ltd 2001
Crude Oil
Crude oil is a mixture; it contains hundreds of different compounds, some small and some extremely large. Nearly all these compounds contain carbon and hydrogen only and are called hydrocarbons.
Hydrocarbons are molecules that contain carbon and hydrogen only.
The compounds present in crude oil are separated, processed and purified in an oil refinery. These processes are covered in the following slides.
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Fuel gas
Petrol
Naphtha
Kerosine
Diesel
Fuel Oil andbitumen
Composition of a typical crude oil
Crude oils from different parts of the world have different composition
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Boiling range
20-70C 70-120C 120-170C
170-240C
Name Petrol Naphtha Kerosine Diesel
Colour Pale yellow Yellow Dark yellow
Light brown
Viscosity Very runny
runny Less runny
Less runny
Combustion Extremely flammable
Very flammable
Less flammable
Less flammable
It is difficult to obtain pure compounds from crude oil so instead, crude oil is separated intogroups of compounds called fractions. Each fraction contains compounds of similar boiling point. A description of each fraction is shown below:
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Fractional distillation
Crude oil is split into fractions using fractional distillation.
Here crude oil is heated and pumped into the bottom of a tall tower containing trays. Compounds with low boiling points rise towards the top of the tower where they condense. Compounds with higher boiling point condense lower in the column. Thus each tray contains liquids (fractions) of different boiling point. The liquid on each tray is continuously pumped away.
A fractional distillation tower works continuously, unlike distillation in the laboratory.
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Crude oil
preheater
Medium ones condense
Short ones condense
Small ones condense
Very small molecules do not condense and come out of the top
Very largemolecules do notvaporise and fallto the bottom
How fractional distillationworks
40°C
70°C
180°C
250°C
340°C
Long ones condense
Liq
uid
ou
t
Get t
ing
coole
r
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Crude oil
Fuel gas
Petrol
Naphtha
Kerosine
Diesel fuel
Fuel and lubricating oil
Bitumen
What fractional distillation produces
Fractional distillationseparates crude oil according to boiling point.
Use
s of
each
fra
ctio
n o
n n
ext
slid
e
Get t
ing
more
vola
t ile
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Fuel gas
Petrol / gasoline
Naphtha
Paraffin / Kerosine
Diesel fuel
Fuel and lubricating oil
Bitumen
Burned in the refinery to fuel the distillation process, sold as LPG, purified and sold as bottled camping gas
Fuel for cars and motorcycles, also used to make chemicals.
Used to make chemicals.
Fuel for greenhouse heaters and jet engines, manufacture of chemicals.
Fuel for lorries, trains.
Fuel for the heating systems of large buildings, fuel for ships, lubricating oil.
Roofing, and road surfaces.
Uses of each fraction
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Fuel gas
Petrol / gasoline
Naphtha
Paraffin / Kerosine
Diesel fuel
Fuel and lubricating oil
Bitumen
1-4, mostly 1.
5-10
8-12.
10-16
14-22
20-70
More than 65
Fraction Number of carbon atoms
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Burning Hydrocarbons
The apparatus below is used to test the products of combustion of a hydrocarbon.
any hydrocarbon + oxygen water + carbon dioxide
Suctionpump
Candle wax is thehydrocarbon here
ice-water
Cloudiness-indicates carbon dioxideLiquid collected
can be tested withanhydrous cobalt chloridepaper (bluepink).
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Alkanes
Carbon atoms are unusual in that they are able to form strong covalent bonds to each other. Therefore, carbon is able to form chains of atoms of different length and so make molecules of different size. There are many thousands of molecules containing C-C bonds. In this course you learn about two groups of these compounds, alkanes and alkenes.
Alkanes are hydrocarbons (molecules containing carbon and hydrogen only) in which each carbon atom is covalently bonded to four other atoms via 4 single covalent bonds. The other atoms can be either carbon or hydrogen.
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Alkanes: Methane, CH4
C
H H
HH
C
H
H
H H
‘Dot and cross’ diagramDisplayed formulaor graphical formula
It is common in organic chemistry to show covalent bonds as single lines. This makes it easier to show how the atoms are connected.
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C
H
HC
H
H
H C
C H
H
H
H
H
H
H
Alkanes: Ethane, C2H6
Ethane is the simplestalkane containing a C-C bond.
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C
H
H
H C
H
H
H
C
H
H
H H
C
H
H
H C
H
H
C
H
H
H
methane, CH4
ethane, C2H6
propane, C3H8
Alkanes
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butane, C4H10
pentane, C5H12
C
H
H
H C
H
H
C
H
H
C
H
H
H
C
H
H
H C
H
H
C
H
H
C
H
H
C
H
H
H
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C
H
H
H C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
H
hexane, C6H14
and so on…………
Notice the carbon chain
is not straight
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methane, CH4
ethane, C2H6
propane, C3H8
butane, C4H10
pentane, C5H12
hexane, C6H14....
Alkane series of molecules
General Formula, CnH2n+2
Since all these molecules contain only single covalent bonds, alkanes are called saturated.
This is called a homologous series
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Alkane Formula MeltingPoint /C
BoilingPoint /C
State atroomtemperature
Methane CH4 -182 -164 gas
Ethane C2H6 -183 -89 gas
Propane C3H8 -188 -42 gas
Butane C4H10 -138 0 gas
Pentane C5H12 -130 36 liquid
Hexane C6H14 -95 69 liquid
Incr
easi
ng m
elt
ing
an
d
boili
ng
poin
t.
Physical Properties of the Alkanes
The alkanes show a gradual change in melting and boiling points.
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CrackingThe demand for some hydrocarbons is high and cannot be supplied from fractional distillation alone. To boost the amount of some smaller hydrocarbons produced some of the high boiling point fractions are converted to more useful hydrocarbons. This process is called cracking.
Cracking involves breaking C-C bonds.
catalyst
smaller alkane
ethene
Heat tovaporise
Long alkane
Distillationtower
pressure
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Cracking
On the surface of the catalyst, long chain molecules are split apart or ‘cracked’. The reaction is:
C CH
H
H
H H
C C C C C C
H
H
H
H
H
H
H
H
H
H
H
H
H
C CH
H
H
H H
C C C C
H
H
H
H
H
H
H
H
H C CH
H
H
H+
C8H18 C6H14 + C2H4
ethene
Octane
hexane
Etheneis usedto makeplastics
Heat pressure
catalyst
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CHEMICAL REACTIONS OF ALKANES
Alkanes are generally unreactive. This is because they only contain C-H and C-C bonds.
However, the lower members of the series readily combust in air. With plenty of air, the products are water and carbon dioxide only.
Methane + oxygen water + carbon dioxide
CH4 + 2O2 2H2O + CO2
Combustion with limited amounts of air, however, producescarbon monoxide and water. Carbon monoxide is a poisonous gas.
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Isomerism
Alkanes of the same molecular formula can have different arrangements of atoms
Extension
C C C C
H
H
H
H
H
H
H
H
H
H C C C
H
H
H
H
H
H
H
C H
H
H
These molecules are isomers of butane
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Alkenes
C
H
H
C
H
H
Ethene is the simplestalkene.
C
H
H
C
H
H
C2H4
Carbon atoms can also form double covalent bonds to each other. Molecules with a double bond are called alkenes.
C CH
H
H
Hor
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Alkenes
Alkenes have the general formula
CnH2n
Alkenes are unsaturated because they contain a double C=C bond. In all alkenes at least two carbon atoms are joined to only 3 atoms.
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Other alkenes
C CC
H
H
H
H
H
HPropene, C3H6
C CH
H H
CCH
H
H
H
HButene, C4H8
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CHEMICAL REACTIONS OF ALKENES
The double bond allows alkenes to undergo reactions where atoms are added to the molecule. Thus, alkenes are more reactive than alkanes.
C CH
H
H
H+ Br2
C C
BrBr
H
HH
H
An addition reaction:
If ethene is bubbled through bromine water the solution becomes colourless - this is used as the test for an alkene. Explanation: bromine colours the solution orange, however, this is used up in the reaction and the product is colourless.
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Pressurehightemperature
catalyst
Polymerisation
Alkenes can undergo addition reactions to other alkene molecules. The result is very long chains of carbon atoms called polymers.
C CH
H
H
HC C
HH
H H
C C C C
H
H
H
H
H
H
H
H
This is written as:
Andlotsmore..
Pressure
high temperaturecatalyst
C CH
H
H
HC C
HH
H H
n
n
This is called addition polymerisation
ethene
poly(ethene)
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Examples of addition polymers
Poly(propene)C CHH
H CH3
n
npropene
n
tetrafluoroethane Poly(tetrafluoroethane)or PTFE
n
C C
F F
F F
C CCH
H H
H
H
H
C CF
F
F
F
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Three very useful plastics
Poly(ethene) Poly(propene) Poly(styrene)
Shopping bagsBottlesBucketsWashing-up bowls
Milk cratesRopeFibres to makecarpets
BoxesFoam packing –insulation and toprotect f romshock.
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Poly(ethene) Bottles(HDPE)
Poly(propene) boxes(PP)
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REVIEW QUESTIONS
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1. i) How is crude oil split into fractionsii) Name the seven fractions produced by fractionaldistillation of crude oil.iii) Give three differences between fractions.
2. i) What is meant by cracking?ii) Complete the formula below:
C8H18 + C2H4
iii) The starting hydrocarbon is octane, name the two products of this reaction.iv) Describe how you could test for the presence of ethene.
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3. i) Draw the bonding diagram for methane (show only outer shell electrons, carbon has an atomic number of 6).ii) Draw the graphical formula for methane.iii) Methane is saturated, explain what this means.iv) Draw the graphical formula for another alkane containing five carbon atoms.
4. Propane is used as ‘Calor Gas’. Complete the word and equation for its combustion in the plenty of airPropane + Oxygen _________ + _________
C3H8 + O2 _____ + ___
Why is it necessary to combust hydrocarbons in plenty ofair?
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5.
i) In a homologous series the physical properties change gradually in the same direction. Plot a graph of boiling point against number of carbons for the alkanes. Use this graph to predict the boiling point of decane, C10H22.
6.
i) Write down the graphical formula for propene.ii) Write down the equation for the reaction of propenewith bromine.iii) Predict the reaction of propene with hydrogen and write down the equation. Iv) What type of reaction is this?
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7.
Using the polymerisation of ethene as an example, explain the term addition polymerisation.
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Harder Questions
8. Draw graphical formula for the three isomers of pentane.
9. Draw graphical formula for three isomers of butene.
10. Write down the equation for the combustion ofpropene in plenty of air and with a restricted amount of air.
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ANSWERS TO REVIEW
QUESTIONS
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1. i) Crude oil is split into ‘fractions’ of different boiling point by fractional distillation. Here crude oil is vaporised and passed into a fractionating tower. Towards the top of the tower, where it is cooler, compounds of low boiling point condense and are collected on trays from which they are removed. Lower in the tower, higher boiling point fractions are collected. ii) Refinery gas / Petrol or gasoline / Naphtha / Kerosine or paraffin / Diesel / Oil / Bitumeniii) boiling point / viscosity / colour / size of hydrocarbon molecule
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2. i) Cracking is the process used to convert long hydrocarbon molecules into smaller ones. The hydrocarbon liquid is vaporised and passed over a catalyst. On the surface of the catalyst the carbon chain is split to produce ethene and a smaller alkane.ii)
C8H18 C6H14 + C2H4
iii) C6H14 is hexane, C2H4 is ethene
iv) You could pass the gas through bromine water. The bromine water, which is orange, will become colourless.
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C
H H
HH
C
H
H
H H
3i) ii)
iii) Methane is saturated because it contains no double bonds.
iv)C
H
H
H C
H
H
C
H
H
C
H
H
C
H
H
H Pentane, C5H12
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Propane + Oxygen carbon dioxide + water
C3H8 + 5O2 3CO2 + 4H2O
4.
In insufficient air/oxygen, carbon monoxide and waterare produced. Carbon monoxide is a poisonous gas.
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Boiling Point Trend in the alkanes
-200-150-100-50
050
100150200
0 1 2 3 4 5 6 7 8 9 10 11
number of carbon atoms
Boili
ng P
oint
/ C
174°C
5.
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C3H6 + Br2 C3H6Br2
C CCH
H H
H
H
H
+ Br2 C C C
Br
H
H H
H
H
H
Br6. propene
C CCH
H H
H
H
H
+ H2 C C CH
H H
H
H
H
H Hpropane
i and ii)
iii)
iv) Addition reaction
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Pressure
high temperaturecatalyst
C CH
H
H
HC C
HH
H H
n
n
This is called addition polymerisation because the molecules of ethene add together without producingany other products.
ethene
poly(ethene)
7.
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C C CH
H H
H
H
H H
C C
H H
H
HH
C C CH
H H
HH H
C
H
H
C HH
H
H
C CH
H
C
H
H
C HH
H
HH
C HH
H
8. Isomers of pentane
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C CC
C
H
H H
HH
H
H
H
C CC
CH
H
H
H
H
H
H
H
C CC
C
H
H
H
H
HH
HH
C CC
H
H
H
H
CH
H
H
H
9. Isomers of butene
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10.
(i) 2C3H6 + 9O2 6CO2 + 6H2O
(ii) C3H6 + 3O2 3CO + 3H2O