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FahadH. Ahmad (Contact: +92 323 509 4443)
ORGANIC CHEMISTRY / IGCSE (0620) / GCE (5070)
Combustion
Fuels are substances that react with oxygen to release useful energy. Most of the energy is
released as heat, but light energy is also released.
About 21 per cent of the air is oxygen. When a fuel burns in plenty of air, it receives enough
oxygen for complete combustion.
Complete combustion
Complete combustion needs a plentiful supply of air so that the elements in the fuel react fully
with oxygen.
Fuels such as natural gas and petrol contain hydrocarbons - which are compounds of hydrogen
and carbon only. When hydrocarbons burn completely:
 the carbon oxidises to carbon dioxide
 the hydrogen oxidises to water (remember that water, H2O, is an oxide of hydrogen)
In general, for complete combustion:
hydrocarbon + oxygen → carbon dioxide + water
Here are the equations for the complete combustion of propane, used in bottled gas:
propane + oxygen → carbon dioxide + water
C3H8 + 5O2 → 3CO2 + 4H2O
Incomplete combustion
Incomplete combustion occurs when the supply of air or oxygen is poor. Water is still
produced, but carbon monoxide and carbon are produced instead of carbon dioxide.
In general, for incomplete combustion:
hydrocarbon + oxygen → carbon monoxide + carbon + water
The carbon is released as soot. Carbon monoxide is a poisonous gas, which is one reason why
complete combustion is preferred to incomplete combustion. Gas fires and boilers must be
serviced regularly to ensure they do not produce carbon monoxide.
Here are the equations for the incomplete combustion of propane, where carbon is produced
rather than carbon monoxide:
propane + oxygen → carbon + water
C3H8 + 2O2 → 3C + 4H2O
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Alcohols
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Alkanes
The alkanes are a homologous series of hydrocarbons. This means that they have similar
chemical properties to each other and they have trends in physical properties. For example, as
the chain length increases, their boiling point increases.
The straight chain alkanes share the same general formula:
The general formula means that the number of hydrogen atoms in an alkane is double the
number of carbon atoms, plus two. For example, methane is CH4 and ethane is C2H6.
Alkane molecules can be represented by displayed formulae in which each atom is shown as its
symbol (C or H) and the covalent bonds between them by a straight line.
Here are the names and structures of five alkanes:
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Alcohols
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Notice that the molecular models on the right show that the bonds are not really at angles of
90°.
Methylpropane
Alkanes are saturated hydrocarbons. This means that their carbon atoms are joined to each
other by single bonds. This makes them relatively unreactive, apart from their reaction with
oxygen in the air - which we call burning or combustion.
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Alcohols
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Butane
Like other homologous series, the alkanes showisomerism. This means that their atoms can be
arranged differently to make slightly differentcompounds with different properties. For
example, an isomer of butane is methylpropane.
Substitution reactions
In a substitution reaction, one atom is swapped with another atom. These are very useful
reactions in the chemical industry because they allow chemists to change one compound into
something more useful, building up designer molecules like drugs.
Alkanes undergo a substitution reaction with halogens in the presence of light.
For instance, in ultraviolet light, methane reacts with halogen molecules such as chlorine and
bromine.
For example:
methane + bromine → methylbromine + hydrogen bromide
CH4 + Br2 → CH3Br + HBr
This reaction is a substitution reaction because one of the hydrogen atoms from the methane is
replaced by a bromine atom.
Alkenes
Alkenes are a homologous series of hydrocarbons that contain a carbon-carbon double bond.
The number of hydrogen atoms in an alkene is double the number of carbon atoms, so they
have the general formula
.
For example, the molecular formula of ethene is
, while for propene it is
.
Here are the names and structures of four alkenes:
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Alkenes are unsaturated, meaning they contain a double bond. This bond is why the alkenes
are more reactive than the alkanes.
Testing for alkenes
The presence of the C=C double bond allows alkenes to react in ways that alkanes cannot.
This allows us to tell alkenes apart from alkanes using a simple chemical test.
Bromine water is an orange solution of bromine. It becomes colourless when it is shaken with
an alkene. Alkenes can decolourise bromine water, but alkanes cannot. The slideshow shows
this process.
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The reaction between bromine and alkenes is an example of a type of reaction called
an addition reaction. The bromine is decolourised because a colourless
dibromo compound forms. For example:
ethene + bromine → dibromoethane
C2H4 + Br2 → C2H4Br2
Other addition reactions of alkenes:
 Hydrogen can be added to a C=C double bond. This has the effect of ‘saturating’ the
molecule, and will turn an alkene into an alkane. For example: C2H4 + H2 → C2H6
 If steam (H2O) is added to an alkene, an alcohol is made. For example: C2H4 + H2O →
C2H5OH
Alcohols
The alcohols are a homologous series of organic compounds. They all contain the functional
group –OH, which is responsible for the properties of alcohols.
The names of alcohols end with ‘ol’, eg ethanol.
The first three alcohols in the homologous series are methanol, ethanol and propanol. They are
highly flammable, making them useful as fuels. They are also used as solvents in marker pens,
medicines, and cosmetics (such as deodorants and perfumes).
Ethanol is the alcohol found in alcoholic drinks such as wine and beer. Ethanol is mixed with
petrol for use as a fuel.
Here are the names and structures of the simplest alcohols:
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Alcohols
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Ethanol from ethene
Structure of ethanol
Ethanol molecules contain carbon, hydrogen and oxygen atoms.
Ethanol from ethene and steam
Ethanol can be manufactured by the hydration of ethene. In this reaction, ethene (which comes
from cracking crude oil fractions) is heated with steam in the presence of a catalyst of
phosphoric acid (to speed up the reaction):
This reaction typically uses a temperature of around 300°C and a pressure of around 60–
70 atmospheres.
Notice that ethanol is the only product. The process is continuous – as long as ethene and steam
are fed into one end of the reaction vessel, ethanol will be produced. These features make it an
efficient process. However, ethene is made from crude oil, which is a non-renewableresource.
Ethene from ethanol
The reaction of ethene with steam to form ethanol can be reversed. This allows ethanol to be
converted into ethene. A catalyst of hotaluminium oxide is used to speed up the reaction.
This is called a dehydration reaction.
Ethanol from sugars
Ethanol can also be made by a process called fermentation.
Fermentation
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Ethanol from ethene
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During fermentation, sugar (glucose) from plant material is converted into ethanol and carbon
dioxide. This typically takes place at temperatures of around 30°C. The enzymes found in
single-celled fungi (yeast) are the natural catalysts that can make this process happen:
Unlike ethene, sugar from plant material is a renewable resource.
Hydration of ethene vs fermentation
These are some of the advantages and disadvantages of making ethanol by hydration of ethene
and by fermentation.
The table compares making ethanol by hydration of ethene (ethene and steam) to making
ethanol by fermentation (sugar from plant material).
Type of raw
materials
Fermentation
Hydration of ethane
Renewable (glucose from
plants)
Non-renewable (ethene from crude
oil)
Type of process Batch (stop-start)
Labour
A lot of workers needed
Rate of reaction Slow
Conditions
needed
Purity of
product
Energy needed
Continuous (runs all the time)
Few workers needed
Fast
Warm (30°C), normal
pressure (1 atm)
High temperature (300°C) and
high pressure (60-70 atm)
Impure (needs treatment)
Pure (no by-products made)
A little
A lot
Biofuels
With fossil fuels being non-renewable and contributing to global warming, biofuels are
increasingly being considered as a possible alternative for the future.
Biofuels are produced from natural products, often plant biomass containing carbohydrate. As
biofuels are produced from plants, they are renewable and theoretically carbon neutral.
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Hydration of ethene vs fermentation
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Some biofuels are produced by using microorganisms to anaerobically ferment carbohydrate
in the plant material - as is the case with bioethanol and biogas production (each process uses
different microorganisms).
Bioethanol
When ethanol is made by fermentation, sugar is converted into ethanol and carbon dioxide if
conditions are anaerobic. Single-celled fungi, called yeast, contain enzymes that are
natural catalysts for making this process happen.
In some countries, such as Brazil, the source of sugar is sugar cane - which yeast can directly
ferment into ethanol. In other countries, plants such as maize are used. Because maize contains
starch rather than sugar, the enzyme amylase must first break down the starch into sugar before
the yeast can ferment it into ethanol.
The ethanol produced by yeast only reaches a concentration of around 15 per cent before the
ethanol becomes toxic to the yeast. In order to make it sufficiently concentrated to be burnt as a
fuel, the ethanol must be distilled.
Disadvantages of bioethanol
There are some disadvantages to growing biofuel crops (such as sugar cane and maize) to be
used as bioethanol:
 The demand for biofuel crops means greater demand on rainforest land.

Crops grow slowly in parts of the world that have lower light levels and temperatures, so
growing biofuel crops in these countries would not satisfy the demand for fuel.

For bioethanol to be burnt in a car engine, some engine modification is needed. Modern
petrol engines can use petrol containing up to 10 per cent ethanol without needing any
modifications, and most petrol sold in the UK contains ethanol.

Although biofuels are in theory carbon neutral, this does not take into account the carbon
dioxide emissions associated with growing, harvesting and transporting the crops, or
producing the ethanol from them. Therefore, overall, more carbon dioxide is emitted than is
absorbed, which means that it contributes to global warming.

Some people morally object to using food crops to produce fuels. For example, it could
cause food shortages or increases in food prices.
Biodiesel
Biodiesel is produced by reacting vegetable oils with methanol. The main product is a
methyl ester of a long chain fatty acid, and this is used as biodiesel. Glycerol is produced as a
by-product.
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Biodiesel can be used as a replacement fuel in most modern diesel engines - unlike raw
vegetable oil, which can only be used in converted or old-fashioned diesel engines.
Carboxylic acids
Carboxylic acids are a group of important organic chemicals. Vinegar contains ethanoic
acid, which is a carboxylic acid. All carboxylic acids have a –COOH functional group, and
have similar reactions as a result. They are weak acids because this functional group is
only partly ionised in solution.
The carboxylic acids are a homologous series of organic compounds. They all contain the
same functional group –COOH.
The names of carboxylic acids end in ‘-oic acid’ – eg ethanoic acid.
In the exam, you will need to be able to recognise the following carboxylic acids from their
names and formulae.
Carboxylic acid Number of C atoms Structural formula Displayed formula
Methanoic acid
1
HCOOH
Ethanoic acid
2
CH3COOH
Propanoic acid
3
CH3CH2COOH
You are not expected to remember the names and formulae of other carboxylic acids.
Ethanoic acid from ethanol
Vinegar is an aqueous solution containing ethanoic acid. Ethanoic acid is formed from the
mild oxidation of the ethanol (which is an alcohol). This can be achieved through:

The addition of chemical oxidising agents - such as acidified potassium dichromate.
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Carboxylic acids
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
The action of microbes in aerobic conditions (in the presence of oxygen). This happens on a
small scale when a bottle of wine is left open and exposed to air. On a commercial scale, it is
achieved in a fermenter using acetic acidbacteria.
Properties of carboxylic acids
Carboxylic acids have the following properties:
1. They dissolve in water to produce acidic solutions (pH less than 7).
2. They react with carbonates to produce carbon dioxide and a salt and water. For example:
calcium carbonate + ethanoic acid → calcium ethanoate + water + carbon dioxide
3. They all react with alcohols, in the presence of an acid catalyst, to form esters. For example:
ethanol + ethanoic acid → ethyl ethanoate + water
Carboxylic acids and esters
Carboxylic acids and esters are organic chemicals that occur naturally and can also be made
from alcohols. The uses of vegetable oils are extended using additives and chemical treatments.
Carboxylic acids
The carboxylic acids are a homologous series of organic compounds.
Carboxylic acids contain the carboxyl functional group (-COOH). Carboxylic acids end in 'oic acid'.
The carboxyl group will never have a position number in a carboxylic acid, as it is always on
the end of the carbon chain.
The basic rules of naming apply. Carboxylic acids take their names from their ‘parent’ alkanes.
For example, ethane is the ‘parent’ alkane of ethanoic acid. Ethanoic acid has the formula
CH3COOH and this structure:
Properties of carboxylic acids
Short carboxylic acids are liquids and are soluble in water. Longer carboxylic acids are solids
and are less soluble in water.
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Properties of carboxylic acids
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The boiling point of a carboxylic acid is higher than that of the alkane with the same number of
carbon atoms because the intermolecular forces are much stronger.
Carboxylic acids are weak acids, so they can donate a hydrogen ion(H+) in acidbase reactions:
This means that they will react with carbonates to produce a salt, water and carbon dioxide:
They will also react with reactive metals to produce a salt and hydrogen.
Making a carboxylic acid
Ethanoic acid can be made by oxidising ethanol (which is an alcohol). In this case, oxidation
involves adding an oxygen atom and removing two hydrogen atoms. This can happen:
 during fermentation if air is present
 when ethanol is oxidised by an oxidising agent, such as acidified potassium manganate(VII)
Making an ester
Esters occur naturally - often as fats and oils - but they can be made in the laboratory by
reacting an alcohol with an organic acid. A little sulfuric acid is needed as a catalyst.
The general word equation for the reaction is:
alcohol + organic acid → ester + water
For example:
methanol + butanoic acid → methyl butanoate + water
The diagram shows how this happens, and where the water comes from:
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Making a carboxylic acid
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So, to make ethyl ethanoate, you would need to react ethanol with ethanoic acid.
What esters smell like
Different esters have different smells. These smells are often fruity. Take a look at the
following four examples:
Alcohol
Organic acid
Ester made
Smell of ester
Pentanol
Ethanoic acid
Pentyl ethanoate
Pears
Octanol
Ethanoic acid
Octyl ethanoate
Bananas
Pentanol
Butanoic acid
Pentyl butanoate
Strawberries
Methanol
Butanoic acid
Methyl butanoate
Pineapples
Fats and oils
Fats and oils are naturally-occurring esters. Fats are solid at room temperature, whereas oils are
liquids.
Vegetable oils
Vegetable oils are natural oils found in seeds, nuts and some fruit. The oil can be extracted. The
plant material is crushed and pressed and the oil, eg olive oil, is squeezed out.
Sometimes the oil is more difficult to extract and has to be dissolvedin a solvent. Once the oil
is dissolved, the solvent is removed bydistillation and impurities (such as water) are also
removed. This leaves pure vegetable oil, eg sunflower oil.
Structure of vegetable oils
Molecules of vegetable oils consist of glycerol and fatty acids.
The diagram shows how three long chains of carbon atoms are attached to a
glycerol molecule to make one molecule of vegetable oil.
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What esters smell like
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The structure of a vegetable oil molecule
Plant oils and their uses
Vegetable oils in cooking
Vegetable oils have higher boiling points than water - so foods can be cooked or fried in
vegetable oils at higher temperatures than they can be if they are cooked or boiled in water.
Food cooked in vegetable oils:
 cook faster than if they were boiled

have different flavours than if they were boiled
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Plant oils and their uses
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Vegetable oils are a source of energy in the diet. Food cooked in vegetable oils releases more
energy when it is eaten than food cooked in water. This can have an impact on our health and
cause excess weight.
Some vegetable oils can be converted to biodiesel by reacting them with methanol. This allows
certain crops to be grown and used to make fuels for cars and lorries without needing to
use fossil fuels. This can help to make biodiesel carbon neutral.
Saturated and unsaturated fats and oils
The fatty acids in some vegetable oils are saturated - they only havesingle bonds between
their carbon atoms. Saturated oils tend to be solid at room temperature, and are sometimes
called vegetable fatsinstead of vegetable oils. Lard is an example of a saturated oil.
The fatty acids in some vegetable oils are unsaturated - they havedouble bonds between some
of their carbon atoms. Unsaturated oils tend to be liquid at room temperature, and are useful for
frying food. They can be divided into two categories:
 monounsaturated fats have one double bond in each fatty acid
 polyunsaturated fats have many double bonds
Unsaturated fats (rather than saturated fats) are thought to be a healthier option in the diet.
Emulsions
Vegetable oils do not dissolve in water. If oil and water are shaken together, tiny droplets of
one liquid spread through the other liquid, forming a mixture called an emulsion.
Emulsions are thicker than the oil or water they contain. This makes them useful in foods such
as salad dressings and ice cream. Emulsions are also used in cosmetics and paints.
There are two main types of emulsion:
 oil droplets in water (milk, ice cream, salad cream, mayonnaise)

water droplets in oil (margarine, butter, skin cream, moisturising lotion)
Emulsifiers
If an emulsion is left to stand, eventually a layer of oil will form on the surface of the water.
Emulsifiers are substances that stabilise emulsions, stopping them separating out. Egg yolk
contains a natural emulsifier. Mayonnaise is a stable emulsion of vegetable oil and vinegar with
egg yolk.
Emulsifier molecules have two different ends:
 a hydrophilic (water-loving) ‘head’ that forms chemical bonds with water but not with oils
 a hydrophobic (water-hating) ‘tail’ that forms chemical bonds with oils but not with water
Lecithin is an emulsifier commonly used in foods. It is obtained from oil seeds and is a mixture
of different substances. A molecular model of one of these substances is seen in the diagram:
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Saturated and unsaturated fats and oils
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Emulsifier molecules
The hydrophilic 'head' dissolves in the water and the hydrophobic 'tail' dissolves in the oil. In
this way, the water and oil droplets become unable to separate out.
Hydrogenation
Bromine water test
Unsaturated vegetable oils contain carbon-carbon double bonds. They can be detected using
bromine water, just as alkenes can be detected in this way. Bromine water becomes colourless
when shaken with an unsaturated vegetable oil, but it stays orange-brown when shaken with
a saturated vegetable fat.
Bromine water can also be used to determine the level of saturation of a vegetable oil.
Hydrogenation
Saturated vegetable fats are solid at room temperature, and have a higher melting point than
unsaturated oils. This makes them suitable for making margarine or for commercial use in the
making of cakes and pastry. Unsaturated vegetable oils can be ‘hardened’ by reacting them with
hydrogen, a reaction called hydrogenation.
The structure of part of a fatty acid
During hydrogenation, vegetable oils are reacted with hydrogen gas at about 60°C. A
nickel catalystis used to speed up the reaction. The double bonds are converted to single bonds
in the reaction. In this way, unsaturated fats can be made into saturated fats – they are hardened.
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Hydrogenation
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Fractional distillation of crude oil
Fractional distillation separates a mixture into a number of different parts, called fractions.
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Fractional distillation of crude oil
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A tall fractionating column is fitted above the mixture, with several condensers coming off at
different heights. The column is hot at the bottom and cool at the top. Substances with
high boiling pointscondense at the bottom and substances with lower boiling points condense
on the way to the top.
Crude oil is a mixture of hydrocarbons. The crude oil is evaporatedand its vapours condense
at different temperatures in the fractionating column. Each fraction contains
hydrocarbon molecules with a similar number of carbon atoms and a similar range of boiling
points.
Oil fractions
The diagram below summarises the main fractions from crude oil and their uses, and the trends
in properties. Note that the gases leave at the top of the column, the liquids condense in the
middle and thesolids stay at the bottom.
The fractionating column
As you go up the fractionating column, the hydrocarbons have:
1. lower boiling points
2. lower viscosity (they flow more easily)
3. higher flammability (they ignite more easily).
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Oil fractions
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Other fossil fuels
Crude oil is not the only fossil fuel.
Natural gas mainly consists of methane. It is used in domestic boilers, cookers and Bunsen
burners, as well as in some power stations.
Coal was formed from the remains of ancient forests. It can be burned in power stations. Coal is
mainly carbon but it may also contain sulfur compounds, which produce sulfur dioxide when
the coal is burned. This gas is a cause of acid rain. Also, as all fossil fuels contain carbon, the
burning of any fossil fuel will contribute to global warmingdue to the production of carbon
dioxide.
Cracking
Fuels made from oil mixtures containing large hydrocarbon molecules are not efficient as they
do not flow easily and are difficult to ignite. Crude oil often contains too many large
hydrocarbon molecules and not enough small hydrocarbon molecules to meet demand. This is
where cracking comes in.
Cracking allows large hydrocarbon molecules to be broken down into smaller, more useful
hydrocarbon molecules. Fractions containing large hydrocarbon molecules are heated
to vaporise them. They are then either:
 heated to 600-700°C

passed over a catalyst of silica or alumina
These processes break covalent bonds in the molecules, causing thermal
decomposition reactions. Cracking produces smaller alkanes and alkenes (hydrocarbons that
contain carbon-carbon double bonds). For example:
hexane → butane + ethene
C6H14 → C4H10 + C2H4
The slideshow shows this process:
Some of the smaller hydrocarbons formed by cracking are used as fuels, and the alkenes are
used to make polymers in plastics manufacture. Sometimes, hydrogen is also produced during
cracking.
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Other fossil fuels
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Combustion of fuels
Complete combustion
Fuels are substances that react with oxygen to release useful energy. Most of the energy is
released as heat, but light energy is also released.
About 21 per cent of air is oxygen. When a fuel burns in plenty of air, it receives enough
oxygen for complete combustion.
Complete combustion needs a plentiful supply of air so that the elements in the fuel react fully
with oxygen.
Fuels such as natural gas and petrol contain hydrocarbons. These are compounds of hydrogen
and carbon only. When they burn completely:
 the carbon oxidises to carbon dioxide
 the hydrogen oxidises to water (remember that water, H 2O, is an oxide of hydrogen)
In general, for complete combustion:
hydrocarbon + oxygen → carbon dioxide + water
Here are the equations for the complete combustion of propane, used in bottled gas:
propane + oxygen → carbon dioxide + water
C3H8 + 5O2 → 3CO2 + 4H2O
Incomplete combustion
Incomplete combustion occurs when the supply of air or oxygen is poor. Water is still
produced, but carbon monoxide and carbon are produced instead of carbon dioxide.
In general for incomplete combustion:
hydrocarbon + oxygen → carbon monoxide + carbon + water
The carbon is released as soot. Carbon monoxide is a poisonous gas, which is one reason why
complete combustion is preferred to incomplete combustion. Gas fires and boilers must be
serviced regularly to ensure they do not produce carbon monoxide.
Carbon monoxide is absorbed in the lungs and binds with the haemoglobin in our red blood
cells. This reduces the capacity of the blood to carry oxygen.
Here are the equations for the incomplete combustion of propane, where carbon is produced
rather than carbon monoxide:
propane + oxygen → carbon + water
C3H8 + 2O2 → 3C + 4H2O
Nitrogen oxides
When fuels are burned in vehicle engines, high temperatures are reached. At these high
temperatures, nitrogen and oxygen from the air combine to produce nitrogen monoxide.
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Combustion of fuels
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nitrogen + oxygen → nitrogen monoxide
N2(g) + O2(g) → 2NO(g)
When this nitrogen monoxide is released from vehicle exhaust systems, it combines with
oxygen in the air to form nitrogen dioxide.
nitrogen monoxide + oxygen → nitrogen dioxide
2NO(g) + O2(g) → 2NO2(g)
Nitrogen dioxide is a cause of acid rain.
Nitrogen monoxide and nitrogen dioxide are jointly referred to as NOx.
Sulfur dioxide and acid rain
Many fossil fuels contain sulfur impurities. When these fuels are burned, the sulfur is oxidised
to form sulfur dioxide.
S(s) + O2(g) → SO2(g)
This sulfur dioxide then dissolves in droplets of rainwater to form sulfurous acid.
SO2(g) + H2O(l) → H2SO3(aq)
Effects of acid rain
Acid rain reacts with metals and rocks such as limestone. Buildings and statues are damaged as
a result.
Acid rain damages the waxy layer on the leaves of trees and makes it more difficult for trees to
absorb the minerals they need for healthy growth. They may die as a result.
Acid rain also makes rivers and lakes too acidic for some aquatic life to survive.
The carbon cycle
Most of the chemicals that make up living tissue contain carbon. When organisms die, the
carbon is recycled so that it can be used by other organisms. The model that describes the
processes involved is called the carbon cycle.
Stages in the carbon cycle
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Sulfur dioxide and acid rain
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Carbon enters the atmosphere as carbon dioxide from respiration and combustion.
1. Carbon dioxide is absorbed by producers to make carbohydrates during the process of
photosynthesis.
2. Animals feed on the plant passing the carbon compounds along the food chain. Most of the
carbon they consume is exhaled as carbon dioxide (formed during respiration). The animals
and plants eventually die.
3. The dead organisms are eaten by decomposers and the carbon is returned to the atmosphere
as carbon dioxide. In some conditions decomposition is blocked. The plant and animal
material may then be available as fossil fuel in the future for combustion.
Note that throughout the processes, carbon is always being recycled.
Methane
Methane, CH4, is a gas that can be produced by:
 decomposition of vegetation

waste gases from digestion in animals
Methane is a powerful greenhouse gas and therefore contributes toglobal warming.
Polymers
Polymers are long chain molecules that occur naturally in living things and can also be made by
chemical processes in industry. Plastics are polymers, so polymers can be extremely useful.
Addition polymers
Alkenes can be used to make polymers.
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Methane
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Polymers are very large molecules made when many smaller molecules join together, end to
end. The smaller molecules are called monomers.
In general:
lots of monomer molecules → a polymer molecule
The polymers formed are called addition polymers.
This slideshow shows how several chloroethene monomers can join end to end to make
poly(chloroethene), also called PVC:
Alkenes can
act as monomers because they are unsaturated:



ethene can polymerise to form poly(ethene), also called polythene
propene can polymerise to form poly(propene), also called polypropylene
chloroethene can polymerise to form poly(chloroethene), also called PVC
Repeating units
Polymer molecules are very large compared with most other molecules, so the idea of a repeat
unit is used when drawing a displayed formula. When drawing one, you need to:
1. change the double bond in the monomer to a single bond in the repeat unit
2. add a bond to each end of the repeat unit
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Repeating units
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Addition polymerisation
It can be tricky to draw the repeat unit of poly(propene). Propene is usually drawn like this:
It is easier to construct the repeat unit for poly(propene) if you redraw the monomer like this:
You can then see how to convert this into the repeat unit.
Condensation polymers
Some polymers are made via condensation polymerisation.
In condensation polymerisation, a small molecule is formed as a by-product each time a bond is
formed between two monomers. This small molecule is often water.
An example of a condensation polymer is nylon.
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Uses of polymers
Different polymers have different properties, so they have different uses. The table gives some
examples:
Polymer
Typical use
Poly(ethene)
Plastic bags and bottles
Poly(propene)
Crates and ropes
Poly(chloroethene)
Water pipes and insulation on electricity cables
Polymers have properties that depend on the chemicals they are made from and the conditions
in which they are made.
For example, there are two main types of poly(ethene) - LDPE, low-density poly(ethene),
and HDPE, high-density poly(ethene). LDPE is weaker than HDPE and becomes softer at
lower temperatures.
Modern polymers are very useful. For instance, they can be used as:
 new packaging materials

waterproof coatings for fabrics (eg for outdoor clothing)

fillings for teeth

dressings for cuts

hydrogels (eg for soft contact lenses and disposable nappy liners)

smart materials (eg shape memory polymers for shrink-wrap packaging)
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Example of the Homologous Series of Alkanes, Structure:
CnH2n+2
Number
Name of Carbon Chemical Simple Structure
Alkane atoms Formula (Molecular Diagram)
Methane
1
C H4
Ethane
2
C2H6
Propane
3
C3H8
Butane
4
C4H10
Pentane
5
C5H12
Hexane
6
C6H14
Heptane
7
C7H16
Octane
8
C8H18
Nonane
9
C9H20
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Decane
10
C10H22
Glossary
1. Alkane Saturated hydrocarbon. A compound of hydrogen and carbon only, with no C=C bonds.
2. Alkene Unsaturated hydrocarbon with a double bond between the carbon atoms.
3. Atom All elements are made of atoms. An atom consists of a nucleus containing protons and
neutrons, surrounded by electrons.
4. complete combustion Burning in a plentiful supply of oxygen or air. Complete combustion of
a hydrocarbon produces water vapour and carbon dioxide.
5. Compound A substance formed by the chemical union of two or more elements.
6. covalent bond A bond between atoms formed when atoms share electrons to achieve a full
outer shell of electrons.
7. double bond A covalent bond resulting from the sharing of four electrons (two pairs) between
two atoms.
8. Element A substance made of one type of atom only.
9. Halogen An element placed in Group 7 of the period table, which starts with fluorine and ends
with astatine.
10.homologous series A 'family' of organic compounds that have the same functional group and
similar chemical properties.
11.Hydrocarbon A compound that contains hydrogen and carbon only.
12.Isomer Chemicals that have the same molecular formula but different arrangements of atoms.
13.Molecule A collection of two or more atoms held together by chemical bonds.
14.Oxidation The gain of oxygen, or loss of electrons, by a substance during a chemical reaction.
15.ultraviolet light Electromagnetic radiation with a greater frequency than visible light but less
than X-rays. Humans cannot see it but it can damage eyes and skin in high doses.
1.
2.
3.
4.
5.
6.
7.
8.
Glossary
amylaseAn enzyme found in yeast, which can break down starch into simple sugars.
anaerobicWithout oxygen.
atmosphereA unit of pressure.
biomassThe dry mass of an organism.
carbon neutralA carbon neutral fuel is one in which the amount of carbon dioxide released
when it is used is equal to amount taken in when it formed.
catalystChanges the rate of a chemical reaction without being changed by the reaction itself.
crackingThe breaking down of large hydrocarbon molecules into smaller, more useful
hydrocarbon molecules by vaporising them and passing them over a hot catalyst.
distillationThe process of separating two liquids with different boiling points.
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9. enzymeProteins which catalyse or speed up chemical reactions.
10.esterA type of organic compound formed in the reaction between an alcohol and a carboxylic
acid.
11.fermentFermentation is an anaerobic process (it takes place in the absence of oxygen).
Fermentation by yeast produces carbon dioxide and ethanol.
12.flammableAble to ignite and burn.
13.Fraction In fractional distillation, such as that of crude oil, the different parts of the original
mixture are called fractions. The substances in each fraction have similar boiling points to each
other.
14.functional group An atom, or group of atoms, that determines the main chemical properties of
an organic compound.
15.global warming The rise in the average temperature of the Earth's surface.
16.glycerolPropane-1,2,3-triol. It reacts with fatty acids to form esters, found in natural as fats and
oils.
17.homologous series A 'family' of organic compounds that have the same functional group and
similar chemical properties.
18.Methanol The simplest alcohol.
19.Microorganism Another name for a microbe. It is microscopic and is an organism, such as a
virus or bacteria.
20.non-renewable A resource that cannot be replaced when it is used up, such as oil, natural gas
or coal.
21.organic compound Compounds that contain carbon atoms, joined by covalent bonds to other
atoms (including other carbon atoms).
22.Solvent The liquid in which the solute dissolves to form a solution.
USE THIS LINK FOR FURTHER INFORMATION
file:///C:/Users/Parasu/Desktop/ORGANIC%20CHEMISTRY/BCCSTUDY%20MATERIALS/BBC%20-%20GCSE%20Chemistry.htm
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