Brown's GCSE/IGCSE KS4 science-CHEMISTRY Revision Notes
Oil, useful products, environmental problems, introduction to
3. ALKANES - saturated hydrocarbons
The alkanes are a series of
hydrocarbon molecules (made of carbon and hydrogen atoms). They are referred to
as 'saturated' hydrocarbons because they do NOT contain a double bond and other
atoms cannot add to them. The physical properties and chemical reactions of
alkanes with oxygen (combustion, burning) and chlorine (to form a chloroalkane)
are fully described with word and symbol equations.
Index of KS4 Science GCSE/IGCSE
Chemistry Oil & Organic Chemistry Pages: 1.
Fossil Fuels : 2. Fractional distillation of crude oil & uses of fractions : 3.
ALKANES - saturated hydrocarbons and combustion : 4.
Pollution, carbon monoxide, nitrogen oxides, what
makes a good fuel?, climate change-global warming :
5. Alkenes - unsaturated hydrocarbons :
6. Cracking - a problem of supply and demand, other products :
7. Polymers, plastics, uses and problems :
8. Introduction to Organic Chemistry - Why so many series of
organic compounds? : 9. Alcohols - Ethanol
- properties, reactions, biofuels :
10. Carboxylic acids and esters : 11. Addition
polymers and condensation polymers :
12. Natural Molecules - carbohydrates - sugars
- starch : 13. Amino acids, proteins,
enzymes & chromatography : 14. Oils, fats,
margarine and soaps :
15. Vitamins, drugs-analgesic medicines & food
additives and aspects of cooking chemistry! : 16. Ozone, CFC's and free
radicals : 17. Extra notes, ideas and links on
Global Warming and Climate Change : Multiple Choice and Gap-Fill Quizzes:
m/c QUIZ on Oil Products (GCSE/IGCSE easier-foundation-level)
m/c QUIZ on Oil Products (GCSE/IGCSE harder-higher-level) :
IGCSE/GCSE m/c QUIZ on other Aspects of Organic Chemistry
3 Easy linked GCSE/IGCSE Oil Products word-fill worksheets
ALKANE series of saturated
are a group of
hydrocarbon molecules in which all the carbon and hydrogen atoms are only
joined by single covalent bonds (e.g. C-H or C-C).
forms four bonds (C-C or C-H) and hydrogen just one bond
(C-H) in alkane hydrocarbon molecules.
are saturated hydrocarbons with the
general formula CnH2n+2 where n is the
number of carbon atoms in the molecule, so ..
when n = 1 you get CH4,
n = 2 gives C2H6, n = 3 gives C3H8
As with naming all organic
molecule series, eth.. means 2 carbon atoms in the chain,
prop... means 3 and but.. means 4 etc. After
that the name is directly derived from the number of carbon atoms in the
chain eg pentane, hexane, heptane, octane
etc. - match with the formulae quoted above.
Alkanes are known as saturated molecules because other atoms cannot
add to them.
Physical properties: The first four in the series are
shown below and are all colourless smelly highly flammable gases. The larger alkanes
are colourless liquids and the biggest members of the series are white
They are not very reactive unless burned!
principal source of alkane hydrocarbons is crude oil - see section 2.
Fractional distillation of crude oil & uses of fractions
is the molecular formula: a summary of the totals of
each atom of each element in one molecule.
is a 'shorthand' version of the full structural formula (3).
is called the structural formula or displayed formula: it shows how all
the atoms are
linked by covalent bonds (the dashes —).
is a '3D' representation of the structural formula (3) showing the
spatial arrangement of the atoms.
is a simple 'molecular diagram' showing the atoms as spheres joined together
Table showing the structure of the first
name of alkane
(main molecule in natural gas)
(1) (2) (3)
in bottled gas
in bottled gas
pentane, hexane and heptane in petrol
octane and nonane
decane, undecane and dodecane
Advanced Level Notes on the
Structure and Naming of Alkanes
3b. The reactions of Alkanes
complete combustion of hydrocarbons (excess
Introduction via coal combustion
The fuel coal
consists mainly of carbon, which, if burned/ignited in excess air,
combusts to form carbon dioxide.
If not enough
air/oxygen is available, coal will only 'half' burn to form the deadly
odourless, colourless and toxic gas carbon monoxide.
+ O2(g) ==> 2CO(g)
This can happen
if organic material, coal or peat is smouldering underground and is
obviously a dangerous situation.
If it was formed
in a domestic coal fire it will quite happily burn with a pale blue
flame to form the 'safe' combustion product carbon dioxide gas.
+ O2(g) ==> 2CO2(g)
Equations for the complete combustion of a
The diagram shows how to detect the
products of hydrocarbon combustion e.g. burning candle wax.
When hydrocarbons are burned in air a fast exothermic reaction occurs releasing heat and forming carbon dioxide and water
- their formation is an oxidation reaction.
It is an oxidation reaction
because of oxygen atom gain by the carbon and hydrogen atoms of the
The carbon dioxide is chemically detected with
limewater - with which it forms a white precipitate (milky
appearance) of calcium carbonate.
The water is chemically detected either by
A physical test
for water is to measure its boiling point
(should be 100oC).
a hydrocarbon molecule (reactant) burns in an excess of air-oxygen
their are only two products of the reaction. The carbon atoms are
oxidised on combining with oxygen to form carbon dioxide molecules, and the
hydrogen atoms are oxidised to water molecules ('hydrogen oxide'). This
section ignores the combustion of the pollutant sulphur.
general word equation: hydrocarbon + oxygen
==> carbon dioxide +
word equations e.g.
methane + oxygen ==> carbon dioxide + water
and the corresponding symbol equation
2O2(g) ==> CO2(g) + 2H2O(l)
Note that one CO2 for every C, and one H2O for every
two H's in the hydrocarbon molecule.
In terms of displayed formula the
equation would be written as ...
... in which every individual atom is
shown and how it is bonded ('connected') with other atoms in the molecule.
All the dashes represent the covalent bonds between the atoms in the
Another example is the combustion of
propane + oxygen ==> carbon
dioxide + water
C3H8(g) + 5O2(g)
==> 3CO2(g) + 4H2O(l)
and in terms of displayed formula
and balancing numbers ...
and the above diagrams show how
the atoms have rearranged themselves in the reaction after the reactant
bonds are broken (C-H, O=O and C-C in ethane etc. below)) and the new bonds
formed in the products (C=O and O-H). Note the number of atoms of each
element must be the same on each side of the equation (1C, 4H's and 4 O's,
Law of Conservation of mass) and the products are different substances with
different properties compared to the reactants. See Elements, Compounds and
Mixtures page for more on
writing and balancing
for ethane the more awkward symbol equation is ...
2C2H6(g) + 7O2(g)
==> 4CO2(g) + 6H2O(l)
and for pentane the symbol equations is ...
==> 5CO2(g) + 6H2O(l)
More on incomplete combustion is
described on the pollution page section 4a
3c. More on ALKANES
- saturated hydrocarbons
- These are obtained directly from crude
oil by fractional distillation (see
oil notes section 2).
- The saturated hydrocarbons form an
homologous series called alkanes with a general formula CnH2n+2
- Saturated means the molecule has no C=C double bonds, only carbon-carbon
single bonds, and so has combined with the
maximum number of atoms i.e.
no atoms can add to it. The alkanes
don't really have a functional group and have quite a limited chemistry
BUT they are still a clearly defined homologous series.
- Alkane examples: The gases
(names and molecular formula): methane CH4,
ethane C2H6, propane C3H8,
butane C4H10, liquids: pentane C5H12,
- The first
four alkane structures are shown above and the names end in ...ane
- Carbon always forms 4 bonds with other
atoms and hydrogen 1 bond
with other atoms e.g.
Propane: molecular formula C3H8,
structural and displayed formula styles include ...
occurs when two or more compounds
have the same chemical formula but have different structures. e.g. for the
molecular formula C4H10 there are two possibilities
- one 'linear' and one with carbon chain 'branching', both
are shown in three ways ...
- and its isomer methylpropane:
Can you work out the structures of the 3
isomers of C5H12 ? (you will find enough to work out
the answers on the
Advanced Level page
- Isomers show variation in physical properties
which depend upon the strength of the intermolecular forces.
Intermolecular forces are due to weak electrical attractive forces that
exist between all molecules.
- (a) For a homologous series the strength of intermolecular forces increases as the carbon chain length
- (b) For isomers (same C number,
molecular formula), the forces
decrease as the amount of chain branching increases.
is because the attractive forces are a function of the potential
surface-surface contact i.e. the compactness of the molecules.
- (a) as the chain length increases the
surface-surface contact must increase per molecule,
- (b) for isomers, with more branching,
the chain length decreases and the molecule is more 'compact' reducing
the surface-surface contact per molecule.
- For example in the series ...
- (a) from methane ... ethane ...
propane ... petrol ... oils ... grease ... waxes etc. the
melting point/boiling point rises and so does the viscosity (stickiness!
less runny, more sticky) as the
carbon chain length increases.
- This trend also indicated by the change
from gases to
liquids to solids ...
- ... illustrated above by the boiling
points of hydrocarbons obtained from crude oil.
- See 2.
Uses of Oil Products page for
more details - the use of alkanes is very strongly linked to their
- (b) 'linear' butane has a higher boiling
point than the 'branched' methylpropane (diagrams above).
Alkanes and alkenes undergo combustion
(halogenoalkanes): Alkanes are
usually not very reactive unless burned!
BUT they will react with reactive chemicals like chlorine
when heated or subjected to uv light to form chlorinated hydrocarbons.
- Despite the reactivity of chlorine you
still need something extra to initiate the
- A substitution reaction occurs
and a chloro-alkane is formed e.g.
- a hydrogen is swapped for a chlorine
and the hydrogen combines with a chlorine atom
- ethane + chlorine ==> chloroethane +
- C2H6 + Cl2
==> C2H5Cl + HCl
+ Cl2 ==>
- Chloro-alkanes are useful
solvents in the laboratory or industry but their vapours can be
Multiple Choice Quizzes and Worksheets
KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products
KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products
KS4 Science GCSE/IGCSE m/c QUIZ on other aspects of Organic Chemistry
3 linked easy Oil Products gap-fill quiz worksheets
ALSO gap-fill ('word-fill') exercises
originally written for ...
... AQA GCSE Science
Useful products from
crude oil AND
... OCR 21st C GCSE Science
Worksheet gap-fill C1.1c Air
pollutants etc ...
... Edexcel 360 GCSE Science
Crude Oil and its Fractional distillation
... each set are interlinked,
so clicking on one of the above leads to a sequence of several quizzes
Level Organic Chemistry revision notes
Revise KS4 Science GCSE/IGCSE/O level
Chemistry Revision-Information Study Notes for revising for AQA GCSE Science, Edexcel
GCSE Science/IGCSE Chemistry & OCR 21stC Science, OCR Gateway Science WJEC/CBAC
GCSE science-chemistry CCEA/CEA GCSE science-chemistry
(and courses equal to US grades 8, 9, 10)
equation keywords: O2 CH4 + 2O2
==> CO2 + 2H2O H2O * C3H8 + 5O2 ==> 3CO2 + 4H2O
+ 7O2 ==> 4CO2 + 6H2O * C2H6 + Cl2 ==>
C2H5Cl + HCl * CH4 + 2O2 ==> CO2 + 2H2O * C3H8 + 5O2 ==> 3CO2 + 4H2O
* 2C2H6 + 7O2 ==> 4CO2 + 6H2O * C2H6 + Cl2 ==>
C2H5Cl + HCl *
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