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TRANSCRIPT
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Unit 2
Everyday Chemistry
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Menu
To work through a topic click onthe title.
Metals
Personal Needs
Fuels
Plastics
End
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Metals
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Finding Metals
Most metals are found combinedwith other elements.
These compounds are called ores. Some metals, including gold, silver
and copper, are found uncombined
in the Earth's crust. This meansthat we can find the element on itsown.
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Extracting Metals
We get somemetals, including
iron, from theirores by heatingthe ore withcarbon.
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We get somemetals, including
aluminium, fromtheir ores usingelectricity.
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Using Metals
The propertiesof metals are thethings it can do and the way it
acts. Metals are chosen for certain uses
because of their properties.
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Densityof a metal is a measure ofhow heavy it is, compared to its
volume. That is why lead weights are used
for fishing lines.
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All metals are good conductors ofheat i.e. they have a high thermal
conductivity. That is why metals are used for
making pots and pans, radiators
etc.
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All metals are good conductors ofelectricity i.e. they have a high
electrical conductivity. That is why metals are used for
making electrical wiring etc.
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Metals are malleable. This meansthat 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.
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Metals are strong.
Metals are used to make many
things because of this strength e.g.car bodies, girders, tools etc.
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Alloys
An alloy is a mixture of metals, orof metals with non-metals.
Many alloys have important uses.
Examples of alloys are:
brass
solder
'stainless' steel
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Reactions of Metals
Metals react with many differentmaterials.
By comparing reactions and seeingthe differences between them wecan recognise the reactivity of
different metals.
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Metals react with oxygen toproduce metal oxides.
Magnesium + Oxygen Magnesium oxide
Aluminium + Oxygen Aluminium oxide
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Some metals react with water toproduce hydrogen.
Sodium + Water Sodium hydroxide + Hydrogen
Potassium + Water Potassium hydroxide + Hydrogen
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Many metals react with dilute acidto produce hydrogen.
Some metals, including copper,silverand gold, do not react withdilute acid.
Zinc + Hydrochloric acid Zinc chloride + Hydrogen
Iron + Sulphuric acid Iron sulphate + Hydrogen
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Test for hydrogen
The test for hydrogen is that itburns with a 'pop'.
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Corrosion
Corrosionis a chemical reaction.
In corrosion the surface of a metal
changing from an element to acompound.
For corrosion to take place the
metal must react with somethingin its surroundings.
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Rusting
Rustingis the corrosion of iron.
Rusting results the iron object
becoming weaker.
Both oxygen(from the air) andwaterare required for rusting.
Rust indicatorcan be used to showthe extent of the rusting process.
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Acid rainincreases the rate ofcorrosion.
Salt spread on roads increases therate of corrosion on car bodywork.
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Preventing Corrosion
Physical protectionpreventscorrosion by making a surface
barrier to air and water.
Now the metal cannot corrodebecause air and/or water cannot
get at the metal.
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Physical protection
Physical protection can be provided by:
Painting
Greasing Electroplating
Galvanising
Tin-plating Coating with plastic
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Chemical protectionpreventscorrosion by using chemicals.
Air and water can still get at themetal, but the chemicals preventcorrosion taking place.
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Chemical protection
Chemical protection can be provided by:
Iron does not rust when attached to
more reactive metals so zinc(galvanising) and scrap magnesium areused to protect iron.
Anodising is a process which increases
the thickness of the oxide layer onaluminium to provide protection againstcorrosion.
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Batteries
In a battery, electricity comes froma chemical reaction.
Batteries require to be replaceddue to the chemicals being used upin the reaction.
Examples of rechargeable batteriesinclude the lead-acid battery andthe nickel-cadmium battery.
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Cells
Electricity can be produced byconnecting different metals together,with a solution containing ions, to forma cell.
The ion solution completes the circuit.
The voltage between different pairs ofmetals varies.
The size of the voltage depends on thedifference in reactivity of the metals.
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Metals
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Personal Needs
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Keeping clean
When cleaning hair, skin andclothes the main problem isoiland
grease. This is because oil and grease do
not dissolve in water.
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Cleaning chemicals are required tobreak up the oil and grease into
tiny droplets These droplets can then mix with
water
This happens because cleaningchemicals dissolve in both waterand oil and grease.
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Some manufactured productscontain cleaning chemicals.
Some are :
Soaps
Detergents
Shampoos
Washing-up liquids and powders.
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Some soaps form a scumwith hardwater.
Soapless detergentsare used toform a lather with hard water.
Dry-cleaning uses special solvents
which are particularly good atdissolving oil and grease stains.
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Clothing
Clothing fabrics are made fromthin strands called fibres.
Fibres are made up of long chainmolecules called polymers.
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Natural fibrescome from plantsand animals.
Some natural fibres are:
silk
wool
cotton
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Synthetic fibresare made by thechemical industry.
Some synthetic fibres are
Nylon
Polyesters(e.g. Terylene)
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Synthetic fibres can be used tomake fabrics which have particular
uses. Dyesare coloured compounds,
which are used to give bright
colours to clothing.
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Chemists have developed ways oftreating 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 wearbecause they soak-up perspiration.
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Personal Needs
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Fuels
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Fire
A fuelis achemical, which isburned to
produce energy.
When a substanceburns it reactswith oxygen.
Combustionisanother word forburning.
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A fire needs:
Fuel
Oxygen (usuallyfrom the air)
A temperature highenough to start thefire and keep it going
Take away anyone ofthe three and the firegoes out.
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Putting out fire
Fire-fighting methods in the laband the home include using
Fire blanket Sand
Water
Carbon dioxide gas
Foam.
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Different methodsof putting out the
fire are used indifferentsituations.
Water must not
be used with oil,petrol andelectrical fires.
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Fossil fuels
Fossil fuelsareformed from animaland plant remains
over a very longperiod of time.
Fossil fuels include
Coal
Natural gas
Oil
Peat.
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Finite Resources
Fossil fuels are finiteresources, i.e. theycannot be replaced.
If we use too muchof the fossil fuels afuel crisis will result,when most of the
fossil fuels havebeen used up.
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Hydrocarbons
The compounds, which are found infossil fuels are mainly hydrocarbons.
A hydrocarbon is a compound whichcontains hydrogen and carbon only.
Hydrocarbons burn in a plentiful supplyof air to produce carbon dioxide and
water. Hydrocarbon + Oxygen Carbon Dioxide + Water
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Renewable resources
Renewable resources are energyresources which can be replaced.
Some renewable sources of energyare:
Methane
Ethanol
Hydrogen
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Methaneis found in biogas, whichis made by the breaking down of
waste plant material. Ethanolis made from sugar cane
and can be mixed with petrol tomake a fuel for cars,
Hydrogen, which can be made fromwater, is a likely fuel for the future.
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Fractional Distillation
Crude oilis a mixture ofhydrocarbons.
A fractionis a group ofhydrocarbons with boiling pointswithin a given range.
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Fractionaldistillationis theprocess whichseparates crudeoil into differentfractions
according to theirboiling points.
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Fractions
Hydrocarbonsmade of smallmolecules boil
more easily thanhydrocarbonsmade of largemolecules.
Different fractionsare used asdifferent fuels.
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The uses of the fractions is decidedby their properties.
How easy it is to make them turninto a gas (evaporate)
Their thickness (viscosity)
How easy they are to burn(flammability)
Their boiling point range
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Cracking
Fractional distillation of crude oilgives more long chain
hydrocarbons than are needed. Crackingis an industrial method
for producing a mixture of smaller,
more useful molecules.
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Water Pollution
Oil spillages cancause greatdamage to marinelife and theenvironment.
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Air Pollution
Soot(carbon) and carbonmonoxide, a poisonous gas, can be
produced when hydrocarbons burnin a low supply of oxygen.
The burning of some fuels releases
sulphur dioxide, a poisonous gas,into the atmosphere.
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Nitrogen and oxygen from the aircan react inside a car engine to
form nitrogen dioxidewhich is apoisonous gas.
Leadcompounds which used to beadded to petrol cause pollution.
Benzenefumes in unleaded petrolare toxic.
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Fuels
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Plastics
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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 decidewhat they are used for.
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Advantages and
disadvantages of plastics
For some uses, plastics haveadvantages over natural materials
and vice versa.
Biodegradablematerials arebroken down by bacteria in the soil
and rot away.
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Most plastics are notbiodegradable and their durability
and lightness can causeenvironmental problems.
Some degradable plastics have
been developed by chemists toease the problems of plastic waste.
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Recycling plastics
Since oil is a finite resource,recyclingis to be encouraged and
chemists are looking for renewablesources of plastics.
Recycling can be difficult because
of the many different kinds ofplastic in common use.
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Different plastics
Plastics can be either thermoplasticorthermosetting.
A thermoplastic is one which can bereshaped on heating.
A thermosetting plastic cannot bereshaped by heating.
The uses of thermosetting plastics aredecided by their heat and electricalinsulation properties.
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Making plastics
Plastics are madeup of polymers.
These are verylong molecules,made by joiningtogether many
small molecules.
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Polymer molecules are made from manysmall molecules called monomers.
The process of making a polymer byjoining many monomers together iscalled polymerisation.
Ethene monomers form poly(ethene),
also called polythene; the styrenemonomers form poly(styrene).
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Plastics
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The End
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