Notes

A formulation is a mixture that has been designed as a useful
product. Many products are complex mixtures in which each
chemical has a particular purpose. Formulations are made by
mixing the components in carefully measured quantities to ensure
that the product has the required properties. Formulations include
fuels, cleaning agents, paints, medicines, alloys, fertilisers and
foods.

Students should be able to identify formulations given appropriate
information.

Students do not need to know the names of components in
proprietary products.

5.8.1.3 Chromatography

Chromatography can be used to separate mixtures and can give
information to help identify substances. Chromatography involves a
stationary phase and a mobile phase. Separation depends on the
distribution of substances between the phases.

The ratio of the distance moved by a compound (centre of spot from
origin) to the distance moved by the solvent can be expressed as its
Rf value:
Rf = distance moved by substance/distance moved by solvent

Different compounds have different Rf
values in different solvents, which can be used to help identify the compounds. The compounds in a mixture may separate into different spots depending on the solvent but a pure compound will produce a single spot in all
solvents.

Students should be able to:

• explain how paper chromatography separates mixtures
• suggest how chromatographic methods can be used for

distinguishing pure substances from impure substances

• interpret chromatograms and determine Rf
values from chromatograms.

Recognise and use
expressions in decimal
form.


Use ratios, fractions and
percentages.

Make estimates of the
results of simple
calculations.

• provide answers to an appropriate number of significant
figures.

Required practical activity 12: investigate how paper chromatography can be used to separate
and tell the difference between coloured substances. Students should calculate Rf
values.

AT skills covered by this practical activity: chemistry AT 1 and 4.
This practical activity also provides opportunities to develop WS and MS. Details of all skills are
given in Key opportunities for skills development (page 183).

5.8.2 Identification of common gases

5.8.2.1 Test for hydrogen

The test for hydrogen uses a burning splint held at the open end of
a test tube of the gas. Hydrogen burns rapidly with a pop sound.

5.8.2.2 Test for oxygen

The test for oxygen uses a glowing splint inserted into a test tube of
the gas. The splint relights in oxygen.

5.8.2.3 Test for carbon dioxide

The test for carbon dioxide uses an aqueous solution of calcium
hydroxide (lime water). When carbon dioxide is shaken with or
bubbled through limewater the limewater turns milky (cloudy).

5.8.2.4 Test for chlorine

The test for chlorine uses litmus paper. When damp litmus paper is
put into chlorine gas the litmus paper is bleached and turns white.

5.9 Chemistry of the atmosphere

The Earth’s atmosphere is dynamic and forever changing. The causes of these changes are
sometimes man-made and sometimes part of many natural cycles. Scientists use very complex
software to predict weather and climate change as there are many variables that can influence this.
The problems caused by increased levels of air pollutants require scientists and engineers to
develop solutions that help to reduce the impact of human activity.

5.9.1 The composition and evolution of the Earth's atmosphere

5.9.1.1 The proportions of different gases in the atmosphere

For 200 million years, the proportions of different gases in the
atmosphere have been much the same as they are today:

• about four-fifths (approximately 80%) nitrogen

• about one-fifth (approximately 20%) oxygen

• small proportions of various other gases, including carbon
dioxide, water vapour and noble gases.


To use ratios, fractions and
percentages.

5.9.1.2 The Earth's early atmosphere

Theories about what was in the Earth’s early atmosphere and how
the atmosphere was formed have changed and developed over
time. Evidence for the early atmosphere is limited because of the
time scale of 4.6 billion years.

One theory suggests that during the first billion years of the Earth’s
existence there was intense volcanic activity that released gases
that formed the early atmosphere and water vapour that condensed
to form the oceans. At the start of this period the Earth’s
atmosphere may have been like the atmospheres of Mars and
Venus today, consisting of mainly carbon dioxide with little or no
oxygen gas.

Volcanoes also produced nitrogen which gradually built up in the
atmosphere and there may have been small proportions of methane
and ammonia.

When the oceans formed carbon dioxide dissolved in the water and
carbonates were precipitated producing sediments, reducing the
amount of carbon dioxide in the atmosphere. No knowledge of other
theories is required.

Students should be able to, given appropriate information, interpret
evidence and evaluate different theories about the Earth’s early
atmosphere.

5.9.1.3 How oxygen increased

Algae and plants produced the oxygen that is now in the
atmosphere by photosynthesis, which can be represented by the
equation:

Algae first produced oxygen about 2.7 billion years ago and soon
after this oxygen appeared in the atmosphere. Over the next billion
years plants evolved and the percentage of oxygen gradually
increased to a level that enabled animals to evolve.

An opportunity to show that
aquatic plants produce
oxygen in daylight.

5.9.1.4 How carbon dioxide decreased

Algae and plants decreased the percentage of carbon dioxide in the
atmosphere by photosynthesis.

Carbon dioxide was also decreased by the formation of
sedimentary rocks and fossil fuels that contain carbon.

Students should be able to:

• describe the main changes in the atmosphere over time and
some of the likely causes of these changes

• describe and explain the formation of deposits of limestone,
coal, crude oil and natural gas.


5.9.2 Carbon dioxide and methane as greenhouse gases

5.9.2.1 Greenhouse gases


Greenhouse gases in the atmosphere maintain temperatures on
Earth high enough to support life. Water vapour, carbon dioxide and
methane are greenhouse gases.

Students should be able to describe the greenhouse effect in terms
of the interaction of short and long wavelength radiation with matter.

5.9.2.2 Human activities which contribute to an increase in greenhouse gases in the
atmosphere


Some human activities increase the amounts of greenhouse gases
in the atmosphere. These include:

• carbon dioxide
• methane.

Students should be able to recall two human activities that increase
the amounts of each of the greenhouse gases carbon dioxide and
methane.

Based on peer-reviewed evidence, many scientists believe that
human activities will cause the temperature of the Earth’s
atmosphere to increase at the surface and that this will result in
global climate change.

However, it is difficult to model such complex systems as global
climate change. This leads to simplified models, speculation and
opinions presented in the media that may be based on only parts of
the evidence and which may be biased.

Students should be able to:

• evaluate the quality of evidence in a report about global
climate change given appropriate information

• describe uncertainties in the evidence base

• recognise the importance of peer review of results and of
communicating results to a wide range of audiences.


5.9.2.3 Global climate change

An increase in average global temperature is a major cause of
climate change.

There are several potential effects of global climate change.
Students should be able to:

• describe briefly four potential effects of global climate change

• discuss the scale, risk and environmental implications of
global climate change.

5.9.2.4 The carbon footprint and its reduction

The carbon footprint is the total amount of carbon dioxide and other
greenhouse gases emitted over the full life cycle of a product,
service or event.

The carbon footprint can be reduced by reducing emissions of
carbon dioxide and methane.

Students should be able to:

• describe actions to reduce emissions of carbon dioxide and
methane

• give reasons why actions may be limited.


5.9.3 Common atmospheric pollutants and their sources

5.9.3.1 Atmospheric pollutants from fuels

The combustion of fuels is a major source of atmospheric
pollutants.

Most fuels, including coal, contain carbon and/or hydrogen and may
also contain some sulfur.

The gases released into the atmosphere when a fuel is burned may
include carbon dioxide, water vapour, carbon monoxide, sulfur
dioxide and oxides of nitrogen.

Solid particles and unburned
hydrocarbons may also be released that form particulates in the
atmosphere.

Students should be able to:

• describe how carbon monoxide, soot (carbon particles), sulfur
dioxide and oxides of nitrogen are produced by burning fuels

• predict the products of combustion of a fuel given appropriate
information about the composition of the fuel and the
conditions in which it is used.


Carbon monoxide is a toxic gas. It is colourless and odourless and
so is not easily detected.

Sulfur dioxide and oxides of nitrogen cause respiratory problems in
humans and cause acid rain.

Particulates cause global dimming and health problems for humans.
Students should be able to describe and explain the problems
caused by increased amounts of these pollutants in the air.


5.10 Using resources

Industries use the Earth’s natural resources to manufacture useful products. In order to operate
sustainably, chemists seek to minimise the use of limited resources, use of energy, waste and
environmental impact in the manufacture of these products.

Chemists also aim to develop ways of
disposing of products at the end of their useful life in ways that ensure that materials and stored
energy are utilised. Pollution, disposal of waste products and changing land use has a significant
effect on the environment, and environmental chemists study how human activity has affected the
Earth’s natural cycles, and how damaging effects can be minimised.

5.10.1 Using the Earth's resources and obtaining potable water

5.10.1.1 Using the Earth's resources and sustainable development

Humans use the Earth’s resources to provide warmth, shelter, food
and transport.

Natural resources, supplemented by agriculture, provide food,
timber, clothing and fuels.

Finite resources from the Earth, oceans and atmosphere are
processed to provide energy and materials.

Chemistry plays an important role in improving agricultural and
industrial processes to provide new products and in sustainable
development, which is development that meets the needs of current
generations without compromising the ability of future generations
to meet their own needs.

Students should be able to:

• state examples of natural products that are supplemented or
replaced by agricultural and synthetic products

• distinguish between finite and renewable resources given
appropriate information.

Students should be able to:

• extract and interpret information about resources from charts,
graphs and tables

• use orders of magnitude to evaluate the significance of data.

Translate information
between graphical and
numeric form.

5.10.1.2 Potable water

Water of appropriate quality is essential for life. For humans,
drinking water should have sufficiently low levels of dissolved salts
and microbes. Water that is safe to drink is called potable water.
Potable water is not pure water in the chemical sense because it
contains dissolved substances.

The methods used to produce potable water depend on available
supplies of water and local conditions.

In the United Kingdom (UK), rain provides water with low levels of
dissolved substances (fresh water) that collects in the ground and in
lakes and rivers, and most potable water is produced by:

• choosing an appropriate source of fresh water

• passing the water through filter beds

• sterilising.

Sterilising agents used for potable water include chlorine, ozone or
ultraviolet light.

If supplies of fresh water are limited, desalination of salty water or
sea water may be required.

Desalination can be done by distillation
or by processes that use membranes such as reverse osmosis.

These processes require large amounts of energy.

Students should be able to:

• distinguish between potable water and pure water

• describe the differences in treatment of ground water and
salty water

• give reasons for the steps used to produce potable water.

Required practical activity 13: analysis and purification of water samples from different sources,
including pH, dissolved solids and distillation.

5.10.1.3 Waste water treatment

Urban lifestyles and industrial processes produce large amounts of
waste water that require treatment before being released into the
environment. Sewage and agricultural waste water require removal
of organic matter and harmful microbes. Industrial waste water may
require removal of organic matter and harmful chemicals.

Sewage treatment includes:

• screening and grit removal

• sedimentation to produce sewage sludge and effluent

• anaerobic digestion of sewage sludge

• aerobic biological treatment of effluent.

Students should be able to comment on the relative ease of
obtaining potable water from waste, ground and salt water.

5.10.1.4 Alternative methods of extracting metals (HT only)

The Earth’s resources of metal ores are limited.

Copper ores are becoming scarce and new ways of extracting
copper from low-grade ores include phytomining, and bioleaching.
These methods avoid traditional mining methods of digging, moving
and disposing of large amounts of rock.

Phytomining uses plants to absorb metal compounds. The plants
are harvested and then burned to produce ash that contains metal
compounds.

Bioleaching uses bacteria to produce leachate solutions that
contain metal compounds.

The metal compounds can be processed to obtain the metal. For
example, copper can be obtained from solutions of copper
compounds by displacement using scrap iron or by electrolysis.

Students should be able to evaluate alternative biological methods
of metal extraction, given appropriate information.

5.10.2 Life cycle assessment and recycling

5.10.2.1 Life cycle assessment

Life cycle assessments (LCAs) are carried out to assess the
environmental impact of products in each of these stages:

• extracting and processing raw materials

• manufacturing and packaging

• use and operation during its lifetime

• disposal at the end of its useful life, including transport and
distribution at each stage.

Use of water, resources, energy sources and production of some
wastes can be fairly easily quantified. Allocating numerical values to
pollutant effects is less straightforward and requires value
judgements, so LCA is not a purely objective process.

Selective or abbreviated LCAs can be devised to evaluate a product
but these can be misused to reach pre-determined conclusions, eg
in support of claims for advertising purposes.

Students should be able to carry out simple comparative LCAs for
shopping bags made from plastic and paper.

LCAs should be done as a
comparison of the impact
on the environment of the
stages in the life of a
product, and only quantified
where data is readily
available for energy, water,
resources and wastes.

Interpret LCAs of materials
or products given
appropriate information.

Recognise and use
expressions in decimal
form.

Use ratios, fractions and
percentages.

Make estimates of the
results of simple
calculations.

Use an appropriate number
of significant figures.

Translate information
between graphical and
numeric form.

AQA GCSE Combined Science: Trilogy 8464. GCSE exams June 2018 onwards. Version 1.1 04 October 2019
Visit aqa.org.uk/8464 for the most up-to-date specification, resources, support and administration 119
5.10.2.2 Ways of reducing the use of resources

The reduction in use, reuse and recycling of materials by end users
reduces the use of limited resources, use of energy sources, waste
and environmental impacts.

Metals, glass, building materials, clay ceramics and most plastics
are produced from limited raw materials. Much of the energy for the
processes comes from limited resources. Obtaining raw materials
from the Earth by quarrying and mining causes environmental
impacts.

Some products, such as glass bottles, can be reused. Glass bottles
can be crushed and melted to make different glass products. Other
products cannot be reused and so are recycled for a different use.

Metals can be recycled by melting and recasting or reforming into
different products. The amount of separation required for recycling
depends on the material and the properties required of the final
product. For example, some scrap steel can be added to iron from a
blast furnace to reduce the amount of iron that needs to be
extracted from iron ore.

Students should be able to evaluate ways of reducing the use of
limited resources, given appropriate information.

5.11 Key ideas
The complex and diverse phenomena of the natural world can be described in terms of a small
number of key ideas in chemistry.

These key ideas are of universal application, and we have embedded them throughout the subject
content. They underpin many aspects of the science assessment and will therefore be assessed
across all papers.

Key ideas in chemistry:

• matter is composed of tiny particles called atoms and there are about 100 different naturally
occurring types of atoms called elements
• elements show periodic relationships in their chemical and physical properties
• these periodic properties can be explained in terms of the atomic structure of the elements
• atoms bond by either transferring electrons from one atom to another or by sharing electrons
• the shapes of molecules (groups of atoms bonded together) and the way giant structures are
arranged is of great importance in terms of the way they behave
• there are barriers to reaction so reactions occur at different rates
• chemical reactions take place in only three different ways:
• proton transfer
• electron transfer
• electron sharing
• energy is conserved in chemical reactions so can therefore be neither created or destroyed.