Limestone is a naturally occurring resource that is quarried and used to make cement, concrete, and other building materials. It is composed mainly of calcium carbonate, which can be decomposed through heating to calcium oxide and carbon dioxide. Calcium oxide reacts with water to form calcium hydroxide, which is used to neutralize acidic soils. Metals are extracted from metal ores through various processes like heating with carbon or electrolysis depending on the reactivity of the metal. New extraction methods are being developed as metal ores become depleted.

1. GCSE
New
Chemistry
Summary
AQA
GCSE Science
New Unit 2
Chemistry
Summary Notes
Prepared and compiled by
Steve Bishop
Science A
Notes

2. AQA GCSE SCIENCE Chemistry Unit 2 summary notes
Page 2 of 32
Contents
C1.1 THE FUNDAMENTAL IDEAS IN CHEMISTRY.....................................................3
C1.1.1 ATOMS ...........................................................................................................................................4
C1.1.2 THE PERIODIC TABLE................................................................................................................6
C1.1.3 CHEMICAL REACTIONS.............................................................................................................7
C1.2 LIMESTONE AND BUILDING MATERIALS ..........................................................8
C1.2.1 CALCIUM CARBONATE..............................................................................................................9
C1.3 METALS AND THEIR USES .....................................................................................11
C1.3.1 EXTRACTING METALS............................................................................................................ 12
C1.3.2 ALLOYS....................................................................................................................................... 15
C1.3.3 PROPERTIES AND USES OF METALS ................................................................................ 16
C1.4 CRUDE OIL AND FUELS...........................................................................................17
C1.4.1 CRUDE OIL................................................................................................................................. 18
C1.4.2 HYDROCARBONS..................................................................................................................... 19
C1.4.3 HYDROCARBONS FUELS....................................................................................................... 20
C1.5 OTHER USEFUL SUBSTANCES FROM CRUDE OIL.....................................21
C1.5.1 OBTAINING USEFUL SUBSTANCES FROM CRUDE OIL................................................. 22
C1.5.2 POLYMERS ................................................................................................................................ 23
C1.5.2 POLYMERS ................................................................................................................................ 23
C1.5.3 ETHANOL.................................................................................................................................... 24
C1.6 PLANT OILS AND THEIR USES .............................................................................25
C1.6.1 VEGETABLE OILS..................................................................................................................... 26
C1.6.2 EMULSIONS ............................................................................................................................... 27
C1.6.3 SATURATED AND UNSATURATED OILS ............................................................................ 28
C1.7 CHANGES IN THE EARTH AND ITS ATMOSPHERE.....................................29
C1.7.1 THE EARTH’S CRUST............................................................................................................. 30
C1.7.2 THE EARTH’S ATMOSPHERE............................................................................................... 31

3. AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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C1.1 The fundamental ideas in chemistry
Atoms and elements are the building blocks of chemistry. Atoms contain protons,
neutrons and electrons. When elements react they produce compounds.
Key words/ concepts
Atom
Element
Compound
Periodic table
Nucleus
Proton
Neutron
Atomic number
Mass number
Energy level
Electron shell
Noble gases
Unreactive
Stable
Molecules
Ions
Covalent bonds
Reaction
Reactants
Products

4. C1.1.1 Atoms
a) All substances are made
atom is called an element.
elements.
Elements are shown in the
The groups contain elements
The numbers above the columns
Li, Na, K, Rb, Cs, Fr are all
b) Atoms of each element
atom of oxygen, and Na represents
The periodic table above shows
c) Atoms have a small central
and around which there are
d) The relative electrical charges
Name of
Proton
Neutron
Electron
AQA GCSE SCIENCE Chemistry Unit 2 summary notes
made of atoms. A substance that is made of only
element. There are about 100 different naturally occurring
the periodic table.
elements with similar properties.
columns show the group number.
all in group I and have similar chemical properties.
element are represented by a chemical symbol, eg O
represents an atom of sodium.
shows the names and the symbols of the elements.
central nucleus, which is made up of protons and
are electrons.
charges are:
of particle Charge
+1
0
Electron –1
AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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only one sort of
occurring
properties.
O represents an
elements.
and neutrons

5. e) In an atom, the number
nucleus. Atoms have no overall
f) All atoms of a particular
different elements have different
g) The number of protons
the protons and neutrons
Lithium has a mass number
It will have 3 protons.
Mass number – atomic number
7 – 3 – 4
It will have 4 neutrons.
For the atom to have no charge
So, there will be 3 electrons.
h) Electrons occupy particular
Each electron in an atom is
electrons in an atom occupy
shells).
This element has 3 protons,
3, so there must be 3 electrons
It will have a mass number
The first two electrons fill the
shell.
It has one electron in the ou
It has two shells (or energy
AQA GCSE SCIENCE Chemistry Unit 2 summary notes
number of electrons is equal to the number of protons
overall electrical charge.
element have the same number of protons.
different numbers of protons.
in an atom of an element is its atomic number.
in an atom is its mass number.
number of 7, its atomic number is 3.
number = the number of neutrons
charge the number of electrons (-) = number of
electrons.
particular energy levels.
is at a particular energy level (in a particular
occupy the lowest available energy levels (innermost
protons, 4 neutrons in its nucleus. The nucleus has
electrons to make the atom neutral.
number of 7 and an atomic number of 3.
the first shell and so the third electron will be
outer shell so it will be in group 1 in the Periodic
energy levels) so it is in period 2 of the Periodic Table.
AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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protons in the
Atoms of
umber. The sum of
of protons (+)
shell). The
(innermost available
has a charge of +
be in the third
Periodic Table
Table.

6. C1.1.2 The periodic
a) Elements in the same group
electrons in their highest energy
similar chemical properties.
The
Chemist
nineteenth
undiscovered
properties
patterns
Columns in the table are known
Rows are known as periods
Groups go down, periods
b) The elements in Group
are unreactive because their
have the maximum number
The noble gases are:
Helium (He)
Neon (Ne)
Argon (Ar)
Krypton (Kr)
Xenon (Xe)
Radon (Rn)
The electron structure
It has two shells (so it is in
(though we call this group
Period 2
AQA GCSE SCIENCE Chemistry Unit 2 summary notes
periodic table
group in the periodic table have the same number
energy level (outer electrons) and this gives them
properties.
The periodic table was first developed by a Russi
Chemist Dmitri Mendeleev (1834-1907) at the
nineteenth century. At the time many elements
undiscovered and Mendelev was able to predict
properties of the yet to be discovered elements
patterns in his Periodic Table.
known as groups
periods
across.
0 of the periodic table are called the noble gases.
their atoms have stable arrangements of electrons
number of electrons possible in their outer shell.
structure of neon is 2, 8:
in period 2) and 8 electrons in its outer shell so
group 0!).
AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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number of
them
Russian
the end of the
elements were
predict the
elements from the
gases. They
electrons. They
so group 8
Group 0

7. C1.1.3 Chemical
a) When elements react, their
involves giving, taking or sharing
Compounds formed from metals
In ions the atoms transfer
Compounds formed from non
In molecules the atoms are
In covalent bonds the atoms
b) Chemical reactions can
carbon
or by symbol equations.
The chemicals before the
products.
c) No atoms are lost or made
equals the mass of the reactants.
On the left there is:
one atom of carbon (C) and
This must balance with the
CO2 is one atom of carbon
There is the same number
the equation is balanced.
AQA GCSE SCIENCE Chemistry Unit 2 summary notes
Chemical reactions
their atoms join with other atoms to form compounds.
sharing electrons to form ions or molecules.
metals and non-metals consist of ions.
transfer (give or take) electrons.
non-metals consist of molecules.
are held together by covalent bonds.
atoms share electrons.
can be represented by word equations:
carbon + oxygen → carbon dioxide
C + O2 → CO2
reactants → products
arrow are the reactants. Those after the arrow
made during a chemical reaction so the mass of
reactants. Atoms are never destroyed or created.
and two atoms in a molecule of oxygen (O2).
the right:
carbon combined with two of oxygen
is the same number of carbon and oxygen atoms on the left as on
balanced.
AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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compounds. This
arrow are the
of the products
created.
on the right, so

8. AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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C1.2Limestone and building materials
Rocks provide essential building materials. Limestone is a naturally occurring
resource that provides a starting point for the manufacture of cement and concrete.
In this section you should be able to:
• know that limestone is needed for buildings and that the positive benefits of
using this material should be considered against the negative aspects of
quarrying.
• consider and evaluate the environmental, social and economic effects of
exploiting limestone and producing building materials from it.
• evaluate the developments in using limestone, cement and concrete as
building materials, and their advantages and disadvantages over other
materials.
Key words
Limestone
Decompose
Thermal decomposition
Salt
Cement
Concrete
Mortar
Chemical compounds
Calcium carbonate CaCO3
Calcium oxide CaO
Carbon dioxide CO2
Calcium hydroxide Ca(OH)2
Limewater
Carbonates

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C1.2.1 Calcium carbonate
a) Limestone, mainly composed of the compound calcium carbonate (CaCO3), is
quarried and can be used as a building material.
b) Calcium carbonate can be decomposed by heating (thermal decomposition) to
make calcium oxide and carbon dioxide.
Calcium oxide is often called quicklime. The word equation is:
calcium carbonate → calcium oxide + carbon dioxide
As a symbol equation:
CaCO3 → CaO + CO2
c) The carbonates of magnesium, copper, zinc, calcium and sodium decompose on
heating in a similar way.
d) Calcium oxide reacts with water to produce calcium hydroxide, which is an alkali
that can be used in the neutralisation of acids.
It reacts with water to form slaked lime, calcium hydroxide.
This reaction gives out lots of heat (exothermic)
calcium oxide + water → calcium hydroxide
CaO + H2O → Ca(OH)2
The two by the bracket means that there are two OH molecules joined with the Ca
atom:
Ca
OH OH
Slaked lime is an alkali so it can be used on acidic soils to increase the pH levels.
Recall: In a chemical reaction atoms are never destroyed or created, but new
substances are formed. We can show this by using symbols (formulae) in the
equations:
calcium carbonate → calcium oxide + carbon dioxide
CaCO3 → CaO + CO2
This is a balanced equation; the number of calcium, oxygen and carbon atoms on
the left hand side balances the number on the right hand side.
The number of atoms of each element is the same on both sides

10. AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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e) A solution of calcium hydroxide in water (limewater) reacts with carbon dioxide to
produce calcium carbonate.
Limewater is used as a test for carbon dioxide. As carbon dioxide is bubbled through
it, it will turn ‘milky’ as the insoluble calcium carbonate if formed.
The equation is:
CO2 + Ca(OH)2 → CaCO3 + H2O
f) Carbonates react with acids to produce carbon dioxide, a salt and water.
For example:
Calcium carbonate + hydrochloric acid → Calcium chloride + carbon dioxide + water
CaCO3 + HCl → CaCl + CO2 + H2O
Salt Carbon dioxide water
This is why limestone (calcium carbonate) is damaged by acid rain.
g) Limestone has a number of uses.
It is heated with clay in a kiln to make cement.
Cement is mixed with sand to make mortar. Mortar is used to bind bricks together.
Cement is mixed with sand and aggregate (loose small chippings) to make concrete.
Concrete is harder than mortar, it is very difficult to compress (squash). It is weak
when it is pulled apart (tension).
Limestone can also be used to make glass. Sand and sodium carbonate are also
needed to make glass.
Making new quarries is always controversial.
The advantages are:
• jobs;
• improved roads;
• more money in the area,
leading to better facilities.
The disadvantages are:
• quarry can be an eyesore;
• dust from the quarry;
• noise from blasting;
• heavy lorry traffic.
Some of these can be resolved by:
• restricted working hours;
• use of rail to transport the minerals;
• restoration of the landscape when mining has stopped.
• have fewer but bigger quarries.

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C1.3Metals and their uses
Metals are very useful in our everyday lives. Ores are naturally occurring rocks that
provide an economic starting point for the manufacture of metals. Iron ore is used to
make iron and steel. Copper can be easily extracted but copper-rich ores are
becoming scarce so new methods of extracting copper are being developed.
Aluminium and titanium are useful metals but are expensive to produce.
Metals can be mixed together to make alloys.
You should be able to:
• consider and evaluate the social, economic and environmental impacts of
exploiting metal ores, of using metals and of recycling metals
• know that metal ores are obtained by mining and that this may involve digging
up and processing large amounts of rock.
• evaluate the benefits, drawbacks and risks of using metals as structural
materials.
Key words
Ores
Alloys
Extraction
Carbon
Oxides
Electrolysis
Furnace
Smelting
Depleted
Phytomining
Bioleaching
Electrode
Corrosion
Conductor
Metals
Elements
Iron
Copper
Aluminium
Titanium
Gold
Transition metals
Alloys
Steel
Compounds
Iron oxide

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C1.3.1 Extracting metals
a) Ores contain enough metal to make it economical to extract the metal. The
economics of extraction may change over time.
Two common ores are bauxite (aluminium ore, Al2O3) and haematite (iron ore Fe2O3)
Bauxite Three different types of haematite
b) Ores are mined and may be concentrated before the metal is extracted and
purified.
c) Unreactive metals such as gold are found in the Earth as the metal itself but most
metals are found as compounds that require chemical reactions to extract the metal.
d) Metals that are less reactive than carbon can be extracted from their oxides by
reduction with carbon.
In simple terms reduction is the removal of oxygen:
Al2O3
reduction
Al
Fe2O3
reduction
Fe

13. Iron oxide (haematite) can
as carbon is more reactive
e) Metals that are more reactive
electrolysis of molten compounds.
extraction of these metals
f) Copper can be extracted
(smelting). The copper can
is limited.
Copper is extracted
electricity.
Copper-rich ores are
major environmental
AQA GCSE SCIENCE Chemistry Unit 2 summary notes
can be reduced with carbon in the blast furnace
reactive than iron. So carbon is able to reduce iron oxide.
reactive than carbon, such as aluminium, are extracted
compounds. The use of large amounts of energy
metals makes them expensive.
extracted from copper-rich ores by heating the ores in
can be purified by electrolysis. The supply of copper
from its ores by chemical processes that involve
are being depleted and traditional mining and extraction
environmental impacts.
AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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furnace to make iron
oxide.
extracted by
energy in the
in a furnace
copper-rich ores
involve heat or
extraction have

14. g) New ways of extracting
the environmental impact
Copper can also be extracted
• phytomining uses plants
are burned to produce ash
be extracted from the ash.
• bioleaching uses bacteria
sulfur and copper. This separates
It has the advantage that it
the traditional method. It has
h) Copper can be obtained
displacement using scrap
During electrolysis positive
i) Aluminium and titanium
carbon. Current methods of
• there are many stages
• large amounts of energy
j) We should recycle metals
expensive in terms of energy
AQA GCSE SCIENCE Chemistry Unit 2 summary notes
extracting copper from low grade ores are being researched
of traditional mining.
extracted by phytomining, or by bioleaching:
plants to absorb metal compounds when they grow.
ash that contains the metal compounds. The metals
ash.
bacteria that can live by using the energy of the bond
separates the metal from the ore.
it is very energy efficient typically using only 30%
has the disadvantage that it is very slow.
obtained from solutions of copper salts by electrolysis
iron.
positive ions move towards the negative electrode (cathode)
cannot be extracted from their oxides by reduction
of extraction are expensive because:
stages in the processes
energy are needed.
metals because extracting them uses limited resources
energy and effects on the environment
AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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researched to limit
grow. The plants
metals can then
bond between
30% to 50 % of
electrolysis or by
(cathode).
reduction with
resources and is

15. AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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C1.3.2 Alloys
a) Iron from the blast furnace contains about 96% iron. The impurities make it brittle
and so it has limited uses.
Cast iron is useful because it is strong in compression.
b) Most iron is converted into steels.
Steels are alloys since they are mixtures (not compounds) of iron with carbon.
Some steels contain other metals such as nickel, chromium and tungsten.
Alloys can be designed to have properties for specific uses.
Low-carbon steels are easily shaped, high-carbon steels are hard, and stainless
steels are resistant to corrosion.
Type of steel
Percentage of
carbon
Uses
Mild steel Up to 0.25% Steel buildings, girders
Medium carbon
steel
0.25% to 0.45%
Car parts
High carbon steel 0.45% to 1.50%
Surgical instruments eg
scalpel
c) Most metals in everyday use are alloys. Pure copper, gold, iron and aluminium are
too soft for many uses and so are mixed with small amounts of similar metals to
make them harder for everyday use.

16. AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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C1.3.3 Properties and uses of metals
a) The elements in the central block of the periodic table are known as transition
metals.
Like other metals they are good conductors of heat and electricity and can be bent or
hammered into shape. They are useful as structural materials and for making things
that must allow heat or electricity to pass through them easily.
b) Copper has properties that make it useful for electrical wiring and plumbing.
Copper:
• is a good conductor of electricity and heat
• can be bent but is hard enough to be used to make pipes or tanks
• it can easily be joined together
• does not react with water
• it is non-magnetic
• it is antibacterial
c) Low density and resistance to corrosion make aluminium and titanium useful
metals.
Aluminium
1) Low density and strength make aluminium ideal for construction of aircraft,
lightweight vehicles, and ladders. An alloy of aluminium called duralumin is
often used instead of pure aluminium because of its improved properties.
2) Easy shaping and corrosion resistance make aluminium a good material
for drink cans and roofing materials.
3) Corrosion resistance and low density leads to its use for greenhouses
and window frames.
4) Good conduction of heat leads to its use for boilers, cookers and
cookware.
5) Good conduction of electricity leads to its use for overhead power cables
hung from pylons (low density gives it an advantage over copper).
6) High reflectivity makes aluminium ideal for mirrors, reflectors and heat
resistant clothing for fire fighting.
Titanium is 60% heavier than aluminium, but it is much stronger. It is nearly half as
light as steel, but it is equally strong.

17. AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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C1.4Crude oil and fuels
Crude oil is derived from an ancient biomass found in rocks. Many useful materials
can be produced from crude oil. Crude oil can be fractionally distilled. Some of the
fractions can be used as fuels. Biofuels are produced from plant material. There are
advantages and disadvantages.
You should be able to:
• evaluate the impact on the environment of burning hydrocarbon fuels
• consider and evaluate the social, economic and environmental impacts of the
uses of fuels
• evaluate developments in the production and uses of better fuels, for example
ethanol and hydrogen
• know and understand the benefits and disadvantages of ethanol and
hydrogen as fuels in terms of:
o use of renewable resources
o storage and use of the fuels
o their products of combustion.
• evaluate the benefits, drawbacks and risks of using plant materials to produce
fuels.
Key words
Crude oil
Compound
Mixture
Distillation
Hydrocarbons
Saturated
Alkanes
Covalent bond
Evaporating
Condense
Fractional distillation
Fractionating column
Particulates
Combustion
Soot
Biofuels
Chemicals
Elements
Sulfur
Carbon
Hydrogen
Compounds
Methane
Ethane
Propane
Butane
Carbon dioxide
Carbon monoxide
Sulfur dioxide
Nitrogen oxides
Ethanol

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C1.4.1 Crude oil
a) Crude oil is a mixture of a very large number of compounds.
b) A mixture consists of two or more elements or compounds not chemically
combined together. The chemical properties of each substance in the mixture are
unchanged. It is possible to separate the substances in a mixture by physical
methods including distillation.
c) Most of the compounds in crude oil consist of molecules made up of hydrogen and
carbon atoms only (hydrocarbons). Most of these are saturated hydrocarbons called
alkanes, which have the general formula CnH2n+2
a) Alkane molecules can be represented in the following forms:
n = 1
n = 2
n = 3
n = 4

19. C1.4.2 Hydrocarbons
b) The many hydrocarbons
which contains molecules
oil and allowing it to condense
This process is fractional distillation.
Candidates should know and
distillation in a fractionating
c) Some properties of hydrocarbons
These properties influence
Fraction
Number
Carbon
atoms
Petroleum
gas
1 to
Naphtha 5 to
Petrol 5 to
Kerosene
(paraffin)
10
Diesel 14
Oil 20
Bitumen 50
AQA GCSE SCIENCE Chemistry Unit 2 summary notes
Hydrocarbons
hydrocarbons in crude oil may be separated into fractions,
with a similar number of carbon atoms, by evaporating
condense at a number of different temperatures.
distillation.
and understand the main processes in continuous
fractionating column.
hydrocarbons depend on the size of their molecules.
influence how hydrocarbons are used as fuels.
Number of
Carbon
atoms
Use
to 4 Heating and cooking
to 9 Making other chemicals
to 10 Fuel for cars and light
aeroplanes
to 16 Fuel for jet or turbine
aeroplanes
- 20 Diesel fuel or heating
- 50 Lubricating oil
or more Making roads
AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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fractions, each of
evaporating the
continuous fractional
molecules.

20. AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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C1.4.3 Hydrocarbons fuels
a) Most fuels, including coal, contain carbon and/or hydrogen and may also contain
some sulfur.
The gases released into the atmosphere when a fuel burns may include:
• carbon dioxide
• water (vapour)
• carbon monoxide
• sulfur dioxide and
• oxides of nitrogen.
Solid particles (particulates - sometimes called soot) may also be released.
b) The combustion of hydrocarbon fuels releases energy. During combustion the
carbon and hydrogen in the fuels are oxidised.
c) Sulfur dioxide and oxides of nitrogen cause acid rain, carbon dioxide causes
global warming, and solid particles cause global dimming.
d) Sulfur can be removed from fuels before they are burned, for example in vehicles.
Sulfur dioxide can be removed from the waste gases after combustion, for example
in power stations.
e) Biofuels, including biodiesel and ethanol, are produced from plant material.
There are economic, ethical and environmental issues surrounding their use.

21. AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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C1.5Other useful substances from crude oil
Fractions from the distillation of crude oil can be broken down (cracked) to make
smaller molecules including unsaturated hydrocarbons such as ethene. Unsaturated
hydrocarbons can be used to make polymers and ethene can be used to make
ethanol. Ethanol can also be made by fermentation.
Key words
Hydrocarbons
Cracked
Molecules
Vapours
Catalyst
Thermal decomposition
Alkanes
Alkenes
Double bond
Cracking
Polymers
Monomers
Biodegradable
Microbes
Hydration
Catalyst
Fermentation
Chemicals
Ethene
Propene
Bromine water
Poly(ethane)
Poly(propene)

22. AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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C1.5.1 Obtaining useful substances from crude oil
a) Hydrocarbons can be cracked to produce smaller, more useful molecules. This
process involves heating the hydrocarbons to vaporise them. The vapours are either
passed over a hot catalyst or mixed with steam and heated to a very high
temperature so that thermal decomposition reactions then occur.
b) The products of cracking include alkanes and unsaturated hydrocarbons called
alkenes. Alkenes have the general formula CnH2n
c) Unsaturated hydrocarbon molecules can be represented in the following forms:
The = represents a double bond.
d) Alkenes react with bromine water, turning it from orange to colourless.
e) Some of the products of cracking are useful as fuels.
The longer chain hydrocarbons are not as useful as fuels because they don’t ignite
easily. However, they can be broken down into shorter chain hydrocarbons which
are more useful. This process is called cracking.
Cracking involves heating the hydrocarbons and passing the vapours produced over
a hot catalyst.
Some of the products of cracking are used as fuels, but others are used to make
plastics.

23. AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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C1.5.2 Polymers
a) Alkenes can be used to make polymers such as poly(ethene) and poly(propene).
In these reactions, many small molecules (monomers) join together to form very
large molecules (polymers).
For example: Candidates should be able to recognise the molecules involved in
these reactions in the forms shown in the subject content.
They should be able to represent the formation of a polymer from a given alkene
monomer.
b) Polymers have many useful applications and new uses are being developed, for
example:
• new packaging materials,
• waterproof coatings for fabrics,
• dental polymers, wound dressings,
• hydrogels,
• smart materials (including shape memory polymers).
Candidates should consider the ways in which new materials are being developed
and used, but will not need to recall the names of specific examples.
c) Many polymers are not biodegradable, so they are not broken down by microbes
and this can lead to problems with waste disposal. Knowledge of specific named
examples is not required, but candidates should be aware of the problems that are
caused by landfill sites and by litter.
d) Plastic bags are being made from polymers and cornstarch so that they break
down more easily. Biodegradable plastics made from cornstarch have been
developed.

24. AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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C1.5.3 Ethanol
a) Ethanol can be produced by hydration of ethene with steam in the presence of a
catalyst.
ethene + steam → ethanol
C2H4 + H2O → C2H5OH
An ethanol plant.
b) Ethanol can also be produced by fermentation with yeast, using renewable
resources. This can be represented by:
sugar → carbon dioxide + ethanol
C6H12O6 → 2CO2 + 2C2H5OH
Using ethane to make ethanol needs non-renewable crude oil as its raw material,
whereas fermentation uses renewable plant material.

25. AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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C1.6Plant oils and their uses
Many plants produce useful oils that can be converted into consumer products
including processed foods. Emulsions can be made and have a number of uses.
Vegetable oils can be hardened to make margarine. Biodiesel fuel can be produced
from vegetable oils
Key words
Emulsions
Biodiesel
Distillation
Emulsifiers
Hydrophilic
Hydrophobic
Saturated
Unsaturated
Double bonds
Catalyst
Hydrogenated
Chemicals
Bromine water
Nickel

26. AQA GCSE SCIENCE Chemistry Unit 2 summary notes
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C1.6.1 Vegetable oils
a) Some fruits, seeds and nuts are rich in oils that can be extracted. The plant
material is crushed and the oil removed by pressing or in some cases by distillation.
Water and other impurities are removed.
Lavender is used to make lavender oil
A field of oilseed rape
b) Vegetable oils are important foods and fuels as they provide a lot of energy. They
also provide us with nutrients.
c) Vegetable oils have higher boiling points than water and so can be used to cook
foods at higher temperatures than by boiling. This produces quicker cooking and
different flavours but increases the energy that the food releases when it is eaten.

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C1.6.2 Emulsions
a) Oils do not dissolve in water.
They can be used to produce emulsions.
Emulsions are thicker than oil or water and have many uses that depend on their
special properties. They provide better texture, coating ability and appearance, for
example in salad dressings, ice creams, cosmetics (such as face creams, body
lotions and lipsticks) and paints.
Milk is another example of an emulsion. It is mainly made up of animal fat and water.
b) Emulsifiers have hydrophilic heads and hydrophobic tails, which are charged. The
tails ‘hate’ water but the heads ‘love’ it. They stop the oil and water in an emulsion
separating out into layers.
The tails dissolve in oil making tiny droplets. The surface of each droplet is made up
of the heads – the heads are charged and so will be repelled by other droplets. In
this way they keep the droplets apart and stop them forming into two layers.

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C1.6.3 Saturated and unsaturated oils
a) Vegetable oils that are unsaturated contain double carbon–carbon bonds (C=C).
These can be detected by reacting with bromine water. The coloured bromine water
will decolourise if the oils are unsaturated.
b) Vegetable oils that are unsaturated can be hardened by reacting them with
hydrogen in the presence of a nickel catalyst at about 60°C.
Hydrogen adds to the carbon–carbon double bonds.
The hydrogenated oils have higher melting points so they are solids at room
temperature, making them useful as spreads and in cakes and pastries. This process
is known as hardening.

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C1.7Changes in the Earth and its atmosphere
Key words/ concepts
Core
Mantle
Crust
Atmosphere
Tectonic plates
Convection currents
Radioactive processes
Hydrocarbons
Algae
Photosynthesis
Sedimentary rocks
Carbonates
Reservoir
Marine environment
Fossil fuels
Chemicals
Nitrogen
Oxygen
Carbon dioxide
Noble gases
Methane
Ammonia
Oxygen

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C1.7.1 The Earth’s crust
a) The Earth
consists of a core,
mantle and crust,
and is surrounded
by the
atmosphere.
b) The Earth’s crust and the
upper part of the mantle are
cracked into a number of large
pieces (tectonic plates).
c) Convection currents within
the Earth’s mantle driven by
heat released by natural
radioactive processes cause
the plates to move at relative
speeds of a few centimetres
per year. The mantle is mostly
solid, but it is able to move slowly.
d) The movements can be sudden and disastrous. Earthquakes and/or volcanic
eruptions occur at the boundaries between tectonic plates.

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C1.7.2 The Earth’s atmosphere
a) For 200 million years, the proportions of different gases in the atmosphere have
been much the same as they are today:
• about four-fifths (80%) nitrogen
• about one-fifth (20%) oxygen
• small proportions of various other gases, including carbon dioxide, water
vapour and noble gases.
b) During the first billion years of the Earth’s existence there was intense volcanic
activity. This activity released the gases that formed the early atmosphere and water
vapour that condensed to form the oceans.
c) There are several theories about how the atmosphere was formed.
One theory suggests that during this period the Earth’s atmosphere was mainly
carbon dioxide and there would have been little or no oxygen gas (like the
atmospheres of Mars and Venus today). There may also have been water
vapour and small proportions of methane and ammonia.
d) There are many theories as to how life was formed billions of years ago.
e) One theory as to how life was
formed involves the interaction
between hydrocarbons,
ammonia and lightning.

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f) Plants and algae produced the oxygen that is now in the atmosphere.
g) Most of the carbon from the carbon dioxide in the air gradually became locked up
in sedimentary rocks as carbonates and fossil fuels.
Carbon dioxide dissolves in the oceans and that limestone was formed from the
shells and skeletons of marine organisms. Fossil fuels contain carbon and
hydrocarbons that are the remains of plants and animals.
h) The oceans also act as a reservoir for carbon dioxide but increased amounts of
carbon dioxide absorbed by the oceans has an impact on the marine environment.
i) Nowadays the release of carbon dioxide by burning fossil fuels increases the level
of carbon dioxide in the atmosphere.
j) Air is a mixture of gases with different boiling points
and can be fractionally distilled to provide a source of
raw materials used in a variety of industrial processes.