AQA AS Chemistry Unit 1 Revision Part 2 -Organic
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Transcript of AQA AS Chemistry Unit 1 Revision Part 2 -Organic
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ORGANIC CHEMISTRY
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What is an Organic Compound?
• An Organic compound contains carbon and hydrogen atoms covalently bonded.
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Three Homologous Series(This is what you need to know for unit 1)
ALKANES (CnH2n+2):
hydrocarbons, mainly used as fuel
ALKENES (CnH2n):
hydrocarbons with double bonds, used to make polymers
HALOALKANES (CnH2n+1X):
contain halogen atoms, CFCs, which are being phased out
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What is a Homologous Series?
Members of a homologous series all have:
the same general formulasimilar chemical propertiesphysical properties show a trendthe same functional group
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Naming Alkanes
No of CarbonAtoms
Formula Name
1
2
3
4
5
6
Alkanes are named after the longest chain of carbon atoms in the molecule
CH4
C2H6
C3H8
C5H12
C4H10
C6H14
Methane
Ethane
Propane
Butane
Pentane
Hexane
Remember - Monsters Eat Pretty Blondes!!!
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Representing Formulae
• Molecular formula
• Actual numbers of atoms of each element present in a molecule e.g. C4H10
• Empirical formula
• Simplest ratio of atoms of each element present in a molecule e.g. C2H5
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Representing Formulae
• Structural formula– Shows the structure of the molecule
H H H H
H—C—C—C—C—H
H H H H
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The structural formula can be abbreviated to emphasise the carbon skeleton
CH3CH2CH2CH3
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Representing Formulae
Displayed formula (shows every bond in the molecule)
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Naming Alkanes
• Branches are named after the number of carbon atoms that they contain:
• 1 carbon = methyl
• 2 carbons = ethyl (very very rare for unit 1)
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Naming Alkanes
• The position of the branch is indicated by a number
• The lowest possible number is used
H H H
H—C—C—C—C—H
H H H H|
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H—C—H
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|H
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2 - methylbutane
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Naming Alkanes
H H
H—C——C——C—H
H H
H—C—H
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H
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H—C—H
H
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2,2-dimethylpropane
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Naming Alkanes
• 2 of a functional group – di
• 3 of a functional group – tri
• 4 of a functional group – tetra
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Cyclo alkanes• Rings of carbon atoms are known as cycloalkanes
• CnH2n
• Note – a cyclo alkane has the same molecular formula as the corresponding straight chain alkene.
• They are Functional group isomers – a type of structural isomer
• E.g.butene and cyclobutane are both C4H8
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Naming haloalkanes
R-F: fluoroalkane R-Cl: chloroalkane R-Br: bromoalkane R-I: iodoalkane
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Naming HaloAlkanes
The position of the halogen must be stated
Example 1-chloro propane 2-chloro
propaneH H
H—C—C—C—H
H H H
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|Cl H H
H—C—C—C—H
H H H
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|Cl
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Naming HaloAlkanes
If there are more than 1 halogen:-
they must be listed in alphabetic orderExample 2-bromo-1-chloropropane 2-chloro-1,1,1,
trifluoropropane
H F
H—C—C—C—F
H H F
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|Cl Br H
H—C—C—C—H
H H H
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|Cl
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Naming Alkenes
• The position of the double bond is indicated by the number of the starting position
Example But-1-eneH H
H—C—C—C—C—H
H H H H
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|—
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Rules for naming organic molecules
1. Count the longest chain. That gives the name of the chain
2. Look for branches and functional groups off the main chain
3. If 2 of the same – di, 3 of the same tri, 4 of the same tetra
4. Put a position number for each, remember start from the shortest end (lowest number.)
5. Where more than one group they must be in alphabetic order
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STRUCTURAL ISOMERS
• These are compounds with the same molecular formula, but with different structural formulae
• e.g. Isomers of C4H10
H H
H—C—C—C—H
H H H
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|H H H H
H—C—C—C—C—H
H H H H
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|H—C—H
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|H
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There are three types of structural isomerism
Chain Isomerism Position Isomerism Functional Group Isomerism Remember - These are all forms of
structural isomerism - molecules have the same molecular formulae, but different structures
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CHAIN ISOMERISM: the carbon chains are arranged differently.Example Butane and Methyl Propane
• Both Isomers of C4H10
H H
H—C—C—C—H
H H H
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|H H H H
H—C—C—C—C—H
H H H H
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|H—C—H
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|H
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POSITION ISOMERISM
the functional group is at a different position on the chain.
Example 1 chloro propane and 2 chloro propane
H H
H—C—C—C—H
H H H
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|Cl H H
H—C—C—C—H
H H H
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|Cl
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FUNCTIONAL GROUP ISOMERISM
the isomers belong to different homologous series.
Example Butene and Cyclobutane
H H
H—C—C
C—C—H
H H
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| H H
H—C—C—C—C—H
H H H H
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|—H
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|H—
—
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THE OIL INDUSTRYTHE OIL INDUSTRY
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Fractional DistillationFractional Distillation
• Crude oil consists of a large number of different hydrocarbons.
• Most of these hydrocarbons are alkanes.
• The alkanes are separated according to their size by fractional distillation.
• Click here to see fractional distillation tower
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Fractional Distillation
• Crude oil is heated and vapour passed into the bottom of a tower
• Top of tower cooler than bottom – I.e. temperature gradient
• This separates mixture into fractions depending on boiling points of hydrocarbons present
• Only those with low boiling points reach top• Others condense in trays at different levels up the
tower and are drawn off here
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Questions• What is passed into the bottom of the tower
• Which hydrocarbons will be piped off at the bottom of the tower
• Why?
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CrackingCracking
• Cracking converts large alkanes into smaller ones which are more useful for making plastics or motor fuel.
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Types of CrackingTypes of Cracking• THERMAL CRACKING• 700 – 1200 K , 70 atmos• Makes alkenes for the plastics
industry.
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Types of CrackingTypes of Cracking• CATALYTIC CRACKING• 720K; 1 atmos; • zeolite catalyst consisting of Silicon
dioxide and Aluminium oxide• Products are mainly Branched and
cyclic products, • Products mainly for motor fuel
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Example and Exercises• Cracking of Decane• Decane → Octane + Ethene• C10H22 → C8H18 + C2H4
• Exercises
1. Write an equation for the thermal cracking of one molecule of C10H22 to give one molecule of propene and one molecule of an alkane only.
2. Write an equation to show the cracking of C14H30 to produce two molecules of butene plus one other molecule.
3. Write an equation to show the cracking of C14H30 to produce hexane and ethene
4. Write an equation to show the cracking of C14H30 to produce one molecule of propene and one molecule of propane and one other molecule
5. Write an equation to illustrate the thermal cracking of one molecule of tetradecane, C14H30in which the products are ethene and propene in the ratio of 2:1, and one other product
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Combustion of AlkanesComplete
Combustion is reaction with oxygen. Complete combustion of a hydrocarbon
produces water plus carbon dioxide. Example: ETHANE + OXYGEN → CARBON DIOXIDE
+ WATER
• C2H6 + 3½O2 → 2CO2 + 3H2O
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Combustion of AlkanesLimited oxygen
When the supply of oxygen is limited, incomplete combustion occurs, and instead of CO2, carbon and carbon monoxide may be formed.
Formation of carbon monoxide (CO: toxic)
• C2H6 + 2½O2 → 2CO + 3H2O
Formation of carbon (soot)
• C2H6 + 1½O2 → 2C + 3H2O
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POLLUTION PROBLEMS
Burning fossil fuels causes these pollutants:
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Types of PollutionCAUSE POLLUTANT PROBLEM
S in fossil fuels reacts with air when burnt
SO2 Produces Acid Rain
High temperature in car engine N2 and O2 in air react
NXOY: : NO, NO2, N2O
Causes acid rain and smog. Makes asthma, bronchitis worse
Lack of oxygen in car engine Heaters not serviced
CO C Unburned hydrocarbon
CO - Toxic C - Unsightly Causes cancer, makes asthma, bronchitis worse
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Exercise: write equations for the reactions below.
The formation of the following oxides of nitrogen from N2 and O2 in the car engine.
a. NO
b. N2O
c. NO2
d. N2O4
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Ways to reduce pollution
• Fit catalytic converters in cars• Use filters in power station chimneys to remove
Sulphur dioxide ( CaO)
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Power Stations Many power stations burn fossil fuels. Sulphur impurities in fossil fuels react to form SO2,
which causes acid rain. Equation: S + O2 → SO2
SO2 + H2O → H2SO3
H2SO3 + ½O 2 → H2SO4 Sulphur dioxide can be removed from emissions by
reaction with calcium oxide. Equation: SO2 + CaO + ½O 2 → CaSO4 The calcium sulphate is used as plaster. This is a neutralisation reaction The process is called flue gas desulfurisation
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Catalytic Converters
Pollution from cars can be reduced by fitting a catalytic converter.
This causes the pollutants to react amongst themselves.
Less harmful substances are formed. Platinum or Rhodium Catalyst Watch this video clip
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Summary of reactions in catalytic converter
In Out
CO CO2
NOx N2
Unburned CO2 + H2O
Hydrocarbons
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Catalyst ConverterExamples of reactions
• 2NO + 2CO → N2 + 2CO2
• 2NO2 + 4CO → N2 + 4CO2
• N2O + CO → N2 + CO2
• C5H12 +16NO → 8N2 + 5CO2 + 6H2O
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Exercise
Write equations to show the reaction of these alkanes with NO:
DECANE (C10H22)
CYCLOHEPTANE (C7H14)
BUTANE (C4H10)
OCTANE (C8H18)
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Global Warming and the Greenhouse effect
Visible radiation (sunlight) readily penetrates atmosphere and warms the earth
Invisible infrared radiation is emitted by the earth and cools it down.
Carbon dioxide traps infrared preventing it escaping – earth’s atmosphere warms up (good in small amounts, bad if too much)
Level of Carbon dioxide has been rising since industrial revolution, causing global warming
Carbon dioxide is called a greenhouse gas Other greenhouse gases are water vapour and methane, the
concentration of these in atmosphere tends to stay roughly the same
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Carbon Neutral Activities
These are activities that produce no overall carbon dioxide emissions into the atmosphere