Term 2: Physical Properties of materials
The properties or characteristics of a material will determine how suitable it is for
use. Properties include strength, boiling and melting points, flexibility, electrical and
heat conductivity. Factors that also need to be taken into account are cost, colour,
texture and mass.
Strength
Strong materials will not bend, break, shatter or deform when subjected to external
forces. Examples include security gates.
Boiling and Melting Points
Melting is when a solid changes into a liquid. A melting point is the temperature at
which the substance will start to melt. Boiling is when a liquid changes into a gas. A
substance’s boiling point is the temperature at which the substance will start melting.
This is when evaporation occurs. Water boils at 100°C.
Flexibility
Materials can bend easily without breaking or being damaged are flexible. Certain
plastics are flexible like a bendy ruler. Plastic lids of aerosol cans of a deodorant
cans are flexible in order to stretch slightly over the top of the can.
Electrical Conductivity
Electrical conductors are good at carrying an electrical current and are metals such
as copper. Materials that cannot carry an electric current are called electrical
insulators and are called non-metals such as plastic.
Heat Conductivity
If heat is able to travel through a material it has good heat / thermal conductivity
(metals). Materials that do not carry heat easily are known as thermal insulators
(nonmetals).
Other Properties (Factors that need to be considered)
Cost
The immediate and long term cost of a material needs to be taken into account when
deciding on its use. For example; a wooden chair may be more expensive but it will
last longer than a plastic chair. Why do you think so? Discuss and give reasons.
Colour
Colour depends on personal taste and may also affect temperature. Darkly coloured
materials get hotter in sunlight (absorb light and warmth), whereas lighter colours
may be cooler (reflect light and warmth). So black will absorb heat and white will
reflect heat.
Texture
Texture refers to how a material feels when you touch it. Some materials need to be
rough (sandpaper) and others need to be smooth (spoon).
Impact on the Environment
Many materials are from the Earth and may be processed to produce other materials
but there is a cost to the environment when these materials are extracted,
processed, transported and used.
Environmental Impact of mining metals
Metals like gold need to be mined. Mining is very important but may lead to many
environmental problems, such as:
Chemicals used can cause water pollution.
Dust can harmful to the health of humans.
Houses built near mine dumps can be affected by dust.
Air pollution causes global warming.
Soil fertility is prohibited as soil is no longer suitable or safe to grow vegetation.
It disrupts the natural habitat of many animal species and destroys ecosystems
Natural habitats are in danger
To reduce this, the mining industry has implemented EIA (Environment Impact
Assessments) which reduces the amount of impact that these factors have on the
environments. Mining companies also have the responsibility to rehabilitate these
areas when the mining project is complete.
Environmental Impact of Plastics
Plastic bags are used every day. While they are useful because they are light, strong
and inexpensive they have a very negative impact on the natural environment:
Contribute to the decline of non-renewable resources (polyethylene comes from a
natural gas that cannot be remade).
Pollution (air, ground and water).
Blocks drains, causing flooding.
Affects animal and human health (choking hazard).
Non bio-degradable items (can take up to 1000 years to break down).
Poisonous (although dumped onto land fill sites, they contaminate the soil and
affect animal health).
Plastics release harmful toxins into the environment
Less plastic needs to be used. Solutions include the re-use of plastic materials as
well as recycling
Environmental Impact of Fuels
Coal, oil and natural gas are very important sources of energy but are bad for the
environment. Fossil fuels also impact on the environment, not only in the mining
process, but also in their uses. They contribute directly to:
Air pollution (fuel in cars).
Oil spills (from ships in the ocean)
Oil spills (can kill animals like seals and their natural habitats)
Separating mixtures
What is a mixture?
A compound is made when different substances bond together in a chemical
reaction. Like methane gas is made when carbon and hydrogen bond together.
A mixture is made when two or more substances mix together without bonding. Like,
sugar and sand. This means a mixture is made up of two or more substances or
materials that have different physical properties. The substances mixed are not
chemically joined and do not change. Mixtures can be made from any number of
components, which can be solids, liquids or gases. Like salad dressing or cold drink.
Compounds are very difficult to separate, but mixtures can be separated.
Separating mixtures
Mixtures can be separated because of their different physical properties.
The methods that can be used to separate mixtures include the following:
Hand sorting
This method involves manually separating the substances in the mixture and can be
used to separate two or more solids when the substances are clearly visible and
large enough to be handled. The substances should be different sizes, shapes and
colours, for this method to work well.
Sieving/sifting
Sieving can also be used to separate different sized solids, if they are too small to
separate using the hand sorting method, for example, sand and stones. This method
can also be used to separate substances that don’t dissolve in a liquid, However,
sieving cannot separate a substance that has dissolved in a solvent. A sieve, which
catches the large particles in the mixture, is used in this method. The smaller
particles fall through the holes in the sieve and can be collected in a container or
bowl. Sieves are also used in a laboratory.
Evaporation
This method is used to separate mixtures which consist of a soluble solid and a
liquid, for example, salt and water. Evaporation is used to obtain a solute from a
solution. The liquid is heated and changes into water vapour (gas), so the water is
removed and the solid remains.
Filtration
This method is used to separate mixtures which are insoluble (do not dissolve), for
example, an insoluble solid and a liquid. Large particles in the mixture are taken out
during the filtration. For example, sand can be separated from sand and water in this
way.The liquid passes through the holes of the filter paper, leaving behind the larger
solid particles. You might also have seen coffee filters and air filters.
Spinning
A liquid can be removed from a solid by spinning. For example, a washing machine
or a tumble drier removes the water from clothes.
Distillation
Distillation is used to obtain the solvent from a solution. This process involves both
evaporation and condensation. The water is heated, evaporates from the solution
and turns to steam. It then cools and condenses in another container and turns back
to water. The salt does not evaporate, it stays behind. The liquid that condenses is
known as the distillate.
Using a magnet
A magnet can be used to separate magnetic materials from non-magnetic materials,
for example, to separate iron and sand. The magnetic substance is attracted to the
magnet and sticks to it, and the non-magnetic substance remains behind.
Chromatography
Chromatography is the study of colours; ‘chrome’ means ‘colours’. There are three
primary colours: red, blue and yellow. These can be mixed to form secondary
colours. The pigments of different colours can be separated. Chromatography is
used to identify colouring agents (chemicals) in foods and inks. This is used in the
food industry and forensic science as more soluble ones rise further than the less
soluble ones and can be separated.
