Products from rocks (summary of the AQA module)

Products from rocks Products from rocks Revision summaryRevision summary

10 April 2023

Atoms, elements and Atoms, elements and compoundscompoundsAll substances are made up of atoms.Elements contain only one type of atom.The atom has a central core called the

nucleus and this is surrounded by fast moving electrons.

Atoms form chemical bonds by giving taking or sharing electrons – the new substance formed is a compound.

All atoms have their own symbols and are shown on the periodic table.

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Chemistry of limestoneChemistry of limestoneLimestone is calcium carbonate

(CaCO3), it is a solids white compound.

Limestone is used in buildings.Limestone decomposes(thermal

decomposition) when heated into quicklime or calcium oxide (CaO) and carbon dioxide (CO2).

Other metal carbonates also decompose on heating.

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Quicklime and slaked limeQuicklime and slaked limeIf water is added to quicklime (CaO)

a lot of heat is released and slaked lime or calcium hydroxide Ca(OH)2 is formed.

Slaked lime, sand and water form mortar. This has been used in building for thousands of years.

The reaction is: Slaked lime + CO2 = calcium carbonate +

water.

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Cement, concrete and Cement, concrete and glassglassHeating limestone with clay in a kiln

produces cement – this hardens much faster than slaked lime mortar.

Concrete is a mixture of stones, sand cement and water. It can be reinforced with steel bars and is very strong.

Glass is made by heating limestone, sand and sodium carbonate.

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Extracting metalsExtracting metalsMetals are usually found combined with

other elements in ores but a few like gold and silver are found naturally (native state).

The reactivity series shows a list of metals from most reactive to least reactive.

Metal oxides can be reduced to the metal and carbon dioxide using carbon.

Metal oxide + carbon = metal + carbon dioxide

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Extracting ironExtracting ironIron ore (haematite or iron oxide)

can be extracted with carbon (coke) in a blast furnace.

Limestone is also added to remove sand in the mix as it forms slag.

Reactions are:C + O2 =CO2

CO2 + C = COFe2O3 + 3CO = 2Fe + 3CO2

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Properties of iron and steelProperties of iron and steelIron made in a blast furnace is 96%

pure, it is called pig iron and is very brittle.

The carbon is removed from the impure iron and other elements are added to make steel.

Steels made with chromium and nickel as alloys are called stainless steel. This type of steel does not rust and is very hard.

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Using alloysUsing alloysBronze is made from copper and

tin – low friction metal.Brass is made from copper and

zinc and is very hard and strong.Gold is alloyed to make it harder.Smart alloys are able to retain their

shape – they are used in medicine and dentistry to help move teeth and bones into the correct position.

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Transition metalsTransition metalsThe transition metals area large

block of metals in the middle of the periodic table.

Their properties include being good conductors of heat and electricity, hard, strong and malleable (bend into shapes).

These properties make these metals ideal for use in construction and manufacturing transport vehicles.

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CopperCopperCopper is the most useful metal in

conduction of electricity.It is extracted from its ore by reacting

with sulphuric acid or smelting (heating) followed by electrolysis.

The above processes use vast amounts of heat and electricity so are not environmentally friendly and expensive.

New methods using bacteria or fungi are being investigated.

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AluminiumAluminiumAluminium has a very low density and

is a good conductor of heat and electricity.

Aluminium does not corrode easily but in its natural state is not very strong, however when it is alloyed with other metals it becomes harder and stronger.

Aluminium is a very reactive metal so it has to be extracted from bauxite (aluminium oxide) ore by electrolysis – this an expensive process.

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TitaniumTitaniumTitanium is a silvery white, strong and

non corrosive metal.It has a very high melting point (1660oC)

which makes it especially useful.It is produced by displacement by a

more reactive metal such as magnesium or sodium.

It is used for jet engines, aircraft bodies, in nuclear reactors and for human joint replacements.

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Fuels from crude oilFuels from crude oilCrude oil contains a mixture of

hydrocarbon molecules.Most of the hydrocarbons in crude

oil are alkanes – these have the general formula CnH2n+2.

Since there are no carbon carbon double bonds in alkanes the molecules are said to be saturated (cannot bond onto any more atoms)

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Fractional distillationFractional distillationCrude oil is separated into different

fractions, containing molecules of different sizes by fractional distillation.

Small molecules have lower boiling points, are of low viscosity (runny), more volatile and flammable, so they are better fuels.

Crude oil vapour is fed into a fractionating column with lower boiling point gases coming off high up the column.

Bitumen for tar road is the highest boiling point fraction.

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Burning fuelsBurning fuelsWhen a fuel is burnt in an oxygen

rich environment carbon dioxide and water vapour are produced.

If too little oxygen is present poisonous carbon monoxide (CO) is produced.

Fuels also produces sulphur dioxide which make acid rain and nitrogen dioxide as well as carbon particles (particulates)

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Cleaner fuelsCleaner fuelsCarbon dioxide gas from burning fuels

is a greenhouse gas. This gas warms the Earth by reducing heat loss from the atmosphere.

The pollution produced by gases such as carbon monoxide, sulphur dioxide and nitrogen oxides can be reduced by treating these gases as they are produced – examples are catalytic converters and desulphurisation chemicals.

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