Transcript Document

Unit 2
Everyday Chemistry
Menu
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the title.
• Metals
• Personal Needs
• Fuels
• Plastics
• End
Metals
Finding Metals
• Most metals are found combined
with other elements.
• These compounds are called ores.
• Some metals, including gold, silver
and copper, are found uncombined
in the Earth's crust. This means
that we can find the element on its
own.
Extracting Metals
• We get some
metals, including
iron, from their
ores by heating
the ore with
carbon.
• We get some
metals, including
aluminium, from
their ores using
electricity.
Using Metals
• The properties of metals are the
things it can do and the way it
acts.
• Metals are chosen for certain uses
because of their properties.
• Density of a metal is a measure of
how heavy it is, compared to its
volume.
• That is why lead weights are used
for fishing lines.
• All metals are good conductors of
heat i.e. they have a high thermal
conductivity.
• That is why metals are used for
making pots and pans, radiators
etc.
• All metals are good conductors of
electricity i.e. they have a high
electrical conductivity.
• That is why metals are used for
making electrical wiring etc.
• Metals are malleable. This means
that they are easily made into new
shapes.
• This property is used when metals
are made into a variety of objects,
such as fencing, horse shoes etc.
• Metals are strong.
• Metals are used to make many
things because of this strength e.g.
car bodies, girders, tools etc.
Alloys
• An alloy is a mixture of metals, or
of metals with non-metals.
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Many alloys have important uses.
Examples of alloys are:
brass
solder
'stainless' steel
Reactions of Metals
• Metals react with many different
materials.
• By comparing reactions and seeing
the differences between them we
can recognise the reactivity of
different metals.
• Metals react with oxygen to
produce metal oxides.
• Magnesium + Oxygen  Magnesium oxide
• Aluminium + Oxygen  Aluminium oxide
• Some metals react with water to
produce hydrogen.
• Sodium + Water  Sodium hydroxide + Hydrogen
• Potassium + Water  Potassium hydroxide + Hydrogen
• Many metals react with dilute acid
to produce hydrogen.
• Some metals, including copper,
silver and gold, do not react with
dilute acid.
• Zinc + Hydrochloric acid  Zinc chloride + Hydrogen
• Iron + Sulphuric acid  Iron sulphate + Hydrogen
Test for hydrogen
• The test for hydrogen is that it
burns with a 'pop'.
Corrosion
• Corrosion is a chemical reaction.
• In corrosion the surface of a metal
changing from an element to a
compound.
• For corrosion to take place the
metal must react with something
in its surroundings.
Rusting
• Rusting is the corrosion of iron.
• Rusting results the iron object
becoming weaker.
• Both oxygen (from the air) and
water are required for rusting.
• Rust indicator can be used to show
the extent of the rusting process.
• Acid rain increases the rate of
corrosion.
• Salt spread on roads increases the
rate of corrosion on car bodywork.
Preventing Corrosion
• Physical protection prevents
corrosion by making a surface
barrier to air and water.
• Now the metal cannot corrode
because air and/or water cannot
get at the metal.
Physical protection
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Physical protection can be provided by:
Painting
Greasing
Electroplating
Galvanising
Tin-plating
Coating with plastic
• Chemical protection prevents
corrosion by using chemicals.
• Air and water can still get at the
metal, but the chemicals prevent
corrosion taking place.
Chemical protection
• Chemical protection can be provided by:
• Iron does not rust when attached to
more reactive metals so zinc
(galvanising) and scrap magnesium are
used to protect iron.
• Anodising is a process which increases
the thickness of the oxide layer on
aluminium to provide protection against
corrosion.
Batteries
• In a battery, electricity comes from
a chemical reaction.
• Batteries require to be replaced
due to the chemicals being used up
in the reaction.
• Examples of rechargeable batteries
include the lead-acid battery and
the nickel-cadmium battery.
Cells
• Electricity can be produced by
connecting different metals together,
with a solution containing ions, to form
a cell.
• The ion solution completes the circuit.
• The voltage between different pairs of
metals varies.
• The size of the voltage depends on the
difference in reactivity of the metals.
Metals
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Personal Needs
Keeping clean
• When cleaning hair, skin and
clothes the main problem is oil and
grease.
• This is because oil and grease do
not dissolve in water.
• Cleaning chemicals are required to
break up the oil and grease into
tiny droplets
• These droplets can then mix with
water
• This happens because cleaning
chemicals dissolve in both water
and oil and grease.
• Some manufactured products
contain cleaning chemicals.
• Some are :
• Soaps
• Detergents
• Shampoos
• Washing-up liquids and powders.
• Some soaps form a scum with hard
water.
• Soapless detergents are used to
form a lather with hard water.
• Dry-cleaning uses special solvents
which are particularly good at
dissolving oil and grease stains.
Clothing
• Clothing fabrics are made from
thin strands called fibres.
• Fibres are made up of long chain
molecules called polymers.
• Natural fibres come from plants
and animals.
• Some natural fibres are:
• silk
• wool
• cotton
• Synthetic fibres are made by the
chemical industry.
• Some synthetic fibres are
• Nylon
• Polyesters (e.g. Terylene)
• Synthetic fibres can be used to
make fabrics which have particular
uses.
• Dyes are coloured compounds,
which are used to give bright
colours to clothing.
• Chemists have developed ways of
treating fabrics to improve their
properties.
• Some fibres form strong bonds with
water molecules
• These fibres are hard to drip-dry but
they do not feel 'sweaty' to wear
because they soak-up perspiration.
Personal Needs
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Fuels
Fire
• A fuel is a
chemical, which is
burned to
produce energy.
• When a substance
burns it reacts
with oxygen.
• Combustion is
another word for
burning.
• A fire needs:
• Fuel
• Oxygen (usually
from the air)
• A temperature high
enough to start the
fire and keep it going
• Take away anyone of
the three and the fire
goes out.
Putting out fire
• Fire-fighting methods in the lab
and the home include using
• Fire blanket
• Sand
• Water
• Carbon dioxide gas
• Foam.
• Different methods
of putting out the
fire are used in
different
situations.
• Water must not
be used with oil,
petrol and
electrical fires.
Fossil fuels
• Fossil fuels are
formed from animal
and plant remains
over a very long
period of time.
• Fossil fuels include
• Coal
• Natural gas
• Oil
• Peat.
Finite Resources
• Fossil fuels are finite
resources, i.e. they
cannot be replaced.
• If we use too much
of the fossil fuels a
fuel crisis will result,
when most of the
fossil fuels have
been used up.
Hydrocarbons
• The compounds, which are found in
fossil fuels are mainly hydrocarbons.
• A hydrocarbon is a compound which
contains hydrogen and carbon only.
• Hydrocarbons burn in a plentiful supply
of air to produce carbon dioxide and
water.
• Hydrocarbon + Oxygen  Carbon Dioxide + Water
Renewable resources
• Renewable resources are energy
resources which can be replaced.
• Some renewable sources of energy
are:
• Methane
• Ethanol
• Hydrogen
• Methane is found in biogas, which
is made by the breaking down of
waste plant material.
• Ethanol is made from sugar cane
and can be mixed with petrol to
make a fuel for cars,
• Hydrogen, which can be made from
water, is a likely fuel for the future.
Fractional Distillation
• Crude oil is a mixture of
hydrocarbons.
• A fraction is a group of
hydrocarbons with boiling points
within a given range.
• Fractional
distillation is the
process which
separates crude
oil into different
fractions
according to their
boiling points.
Fractions
• Hydrocarbons
made of small
molecules boil
more easily than
hydrocarbons
made of large
molecules.
• Different fractions
are used as
different fuels.
• The uses of the fractions is decided
by their properties.
• How easy it is to make them turn
into a gas (evaporate)
• Their thickness (viscosity)
• How easy they are to burn
(flammability)
• Their boiling point range
Cracking
• Fractional distillation of crude oil
gives more long chain
hydrocarbons than are needed.
• Cracking is an industrial method
for producing a mixture of smaller,
more useful molecules.
Water Pollution
• Oil spillages can
cause great
damage to marine
life and the
environment.
Air Pollution
• Soot (carbon) and carbon
monoxide, a poisonous gas, can be
produced when hydrocarbons burn
in a low supply of oxygen.
• The burning of some fuels releases
sulphur dioxide, a poisonous gas,
into the atmosphere.
• Nitrogen and oxygen from the air
can react inside a car engine to
form nitrogen dioxide which is a
poisonous gas.
• Lead compounds which used to be
added to petrol cause pollution.
• Benzene fumes in unleaded petrol
are toxic.
• Soot particles, produced when
diesel fuel does not burn properly,
are harmful.
• Air pollution from the burning of
hydrocarbons can be reduced by
the use of catalytic converters
which convert the pollutant gases
to harmless gases.
Fuels
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Plastics
Plastics
• Plastics are synthetic materials, i.e.
made by the chemical industry.
• Most plastics are made from oil.
• Examples of plastics include polythene,
polystyrene, perspex, PVC, nylon,
Kevlar, bakelite, formica and silicones.
• The properties of plastic help to decide
what they are used for.
Advantages and
disadvantages of plastics
• For some uses, plastics have
advantages over natural materials
and vice versa.
• Biodegradable materials are
broken down by bacteria in the soil
and rot away.
• Most plastics are not
biodegradable and their durability
and lightness can cause
environmental problems.
• Some degradable plastics have
been developed by chemists to
ease the problems of plastic waste.
Disposing of plastics
• Some plastics burn or smoulder to give
off toxic fumes, including carbon
monoxide.
• We can get rid of plastics by burning,
recycling and burying.
• With burning the heat produced can be
used as a source of energy but there are
problems with gases given off.
Recycling plastics
• Since oil is a finite resource,
recycling is to be encouraged and
chemists are looking for renewable
sources of plastics.
• Recycling can be difficult because
of the many different kinds of
plastic in common use.
Different plastics
• Plastics can be either thermoplastic or
thermosetting.
• A thermoplastic is one which can be
reshaped on heating.
• A thermosetting plastic cannot be
reshaped by heating.
• The uses of thermosetting plastics are
decided by their heat and electrical
insulation properties.
Making plastics
• Plastics are made
up of polymers.
• These are very
long molecules,
made by joining
together many
small molecules.
• Polymer molecules are made from many
small molecules called monomers.
• The process of making a polymer by
joining many monomers together is
called polymerisation.
• Ethene monomers form poly(ethene),
also called polythene; the styrene
monomers form poly(styrene).
Plastics
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The End
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