Changing Materials

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Changing Materials
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Contents

• Useful Products from Oil
• Useful Products from Metal Ores
• Useful Products from Rocks
• Useful Products from Air
• Representing Reactions
• Quantitative Chemistry
• Changes to the Earth and Atmosphere
• The Rock Record

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Useful Products From Oil

• What is crude oil?
• Fractional distillation
• Cracking and its products
• Fuels
• Plastics

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What is crude oil?

• Crude oil is a mixture of a very large number of
  compounds.
• It is formed from the remains of plants and
  animals which died millions of years ago. This is
  why it is called a fossil fuel.
• Most of the compounds in crude oil consist of
  molecules made up of hydrogen and carbon atoms
  only, we call these type of compounds
  hydrocarbons.
• We represent hydrocarbons in the following ways

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Fractional Distillation

• The many hydrocarbons in crude oil may be
  separated into fractions, each of which contains
  molecules of a similar size, by evaporating the
  oil and allowing it to condense at a number of
  different temperatures. This process is called
  fractional distillation.

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Cracking and its Products

• There is a much greater demand for shorter
  hydrocarbon than there is for the longer
  hydrocarbons.
• Long chain hydrocarbons can be broken into
  smaller hydrocarbons, by heating with a catalyst.
• This is a thermal decomposition reaction known as
  cracking.
• Cracking produces two types of hydrocarbon
• Alkanes with only single covalent bonds
• Alkenes with one or more double covalent bonds

Test for alkenes alkenes turn bromine water
from brown to colourless.
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Fuels

• Most fuels contain carbon and/or hydrogen and may
  also contain some sulphur. The gases released
  into the atmosphere when a fuel burns may
  include
• carbon dioxide
• water (vapour), which is an oxide of hydrogen
• sulphur dioxide
• This gas dissolves in rain and forms acid rain.

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Plastics

• Alkenes are reactive and so are useful for making
  many other substances including polymers.
  Polymers have very large molecules. They are
  formed when many small molecules join together.
  This process is called polymerisation.
• When alkenes join together to form a polymer with
  no other substance being produced in the
  reaction, the process is called addition
  polymerisation.
• Plastics are polymers and are made by
  polymerisation.
• For example, poly(ethene) (often called
  polythene) is made by polymerising the simplest
  alkene, ethene.

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Useful Products from Rocks

• Metal Ores and Reactivity
• The Blast Furnace
• Extraction of Aluminium
• Purification of Copper
• Corrosion

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Metals Ores and Reactivity

• Rocks from the Earth contain many useful metals.
• Most metals are combined with other elements in
  materials called ores and have to be extracted
  using various methods.
• How each metal is extracted depends on how
  reactive it is.
• Gold is a very unreactive metal and is found as a
  pure metal, because of this it has been in use
  for many thousands of years despite of being a
  very rare metal.
• Iron and copper are more reactive than gold but
  less reactive than carbon, these can be extracted
  from their ores by simply heating with coke these
  have been known for several thousand years
• Aluminium is the most common metal in the Earths
  crust, however, was only discover 200 years ago
  because it is a relatively reactive metal which
  is hard to extract from its ore.

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Extracting iron using the blast furnace.

• A metal such as iron, which is less reactive than
  carbon, can be extracted from its ore using
  carbon
• Reactions in the blast furnace.
• C O2 ? CO2
• The coke burns, to form carbon dioxide and to
  produce heat
• CO2 C ? 2CO
• The carbon dioxide reacts with more hot coke to
  produce carbon monoxide gas.
• 3CO Fe2O3 ? 2Fe 3CO2
• The carbon monoxide removes the oxygen from the
  iron ore this is called reduction.
• The main impurity in the iron ore is silica this
  reacts with the limestone to produce slag
  (calcium silicate)

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Extraction of Aluminium

• Aluminium is made by the electrolysis of bauxite.
• Cryolite is added to lower the melting point of
  bauxite.
• This is a very expensive process and aluminium is
  only made in this way because it cannot be
  prepared by heating with carbon because it is too
  reactive
• At the negative electrode
• Al3 3e- ? Al (REDUCTION)
• At the positive electrode
• 2O2- ? O2 4e- (OXIDATION)

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Purification of Copper

• Copper can be extracted from its ore by reduction
  with carbon, however, this is only 98 pure.
• Copper can be purified by electrolysis using a
  positive electrode made of the impure copper and
  a negative electrode of pure copper in a solution
  containing copper ions.
• When the current is switched on copper ions in
  solution are attracted to the negative and
  electrode and deposited there. Copper atoms in
  the impure block lose electrons and become
  positive ions and go into the solution, replacing
  those which were deposited at the negative
  electrode.
• Eventually the impure block disappears leaving
  behind the impurities and the pure block becomes
  larger.

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Corrosion

• Iron rusts in the presence of oxygen and water.
• Barriers such as paint or grease can be used to
  prevent corrosion.
• Zinc blocks can be attached to iron objects. As
  zinc is more reactive than iron it will corrode
  preferentially thus preventing the iron from
  corroding. This is called sacrificial protection

Aluminium is a very reactive metal but it can be
used without protection against corrosion. This
is because it has a thin lay of oxide which
sticks very firmly to the aluminium and protects
it against further corrosion.
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Limestone
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Useful Products from Air

• Manufacture of ammonia from air
• Manufacture of fertiliser from ammonia
• Problems caused by the over use of fertilisers.

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Manufacture of ammonia from air

• Nitrogen and Hydrogen are needed to make Ammonia.
• Nitrogen is obtained from the air.
• Hydrogen is obtained from water and natural gas.

• The Haber process is a reversible reaction
• This means that the reaction occurs in both
  directions
• High pressures favour the production of ammonia,
  however it expensive to make industrial equipment
  to cope with high pressures.
• Low temperatures favour the production of
  ammonia, however at low temperatures the reaction
  would be too slow to be commercially viable.
• The Haber process makes a compromise with these
  two and recycles the unreacted hydrogen and
  nitrogen

N2(g) 3H2(g) Â 2NH3(g)
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Manufacture of fertiliser from ammonia
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Problems cause by the over use of fertiliser

• Plants need several types of nutrients. Nitrogen
  based nutrients are used to make proteins.
• Farmers can use natural sources of these
  nutrients or synthetic nutrients.
• If fertilisers are over used the excess can wash
  into streams. Plants and green algae grow out of
  control. When they, die bacteria feed off of the
  dead plant material The bacteria increase in
  number, they use up all the oxygen in the water.
  Then the fish die. This process is called
  eutrophication.
• Too many nitrates in the drinking water can also
  cause problems. It can interfere with the bloods
  ability to carry oxygen. This can be especially
  severe in children and babies, causing them to
  turn ble and even die.

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Representing Equations

• When we can represent reactions by word and
  symbol equations
• methane oxygen? carbon dioxide water
• or CH4 O2 ? CO2 H2O
• To this we can add state symbols to give more
  information about the substances
• (s) solid, (l) liquid, (g) gas, (aq)
  aqueous
• CH4(g) O2(g) ? CO2(g) H2O(g)
• This doesnt tell us the whole story we need to
  balance the equation to show that we have not
  destroyed or made new atoms.

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Balancing Equations

• CH4(g) O2(g) ? CO2(g) H2O (g)
• Remember that the formulae for each compound is
  correct you cannot change CH4 to CH3 just to make
  the atoms add up.
• Balance one type of atom at a time
• There is one carbon atom on each side so we can
  leave that alone, however there are 4 H atoms on
  the left hand side and 2 on the right hand side
  we can correct this by putting a 2 in front of
  the water.
• CH4 (g) O2 (g) ? CO2 (g) 2H2O (g)
• Now both the carbon and the hydrogen balance,
  that just leaves us with the oxygen. There are 2
  O on the left hand side and 4 on the right hand
  side. We can correct this by putting a 2 in front
  of the oxygen on the left hand side
• CH4 (g) 2O2 (g) ? CO2 (g) 2H2O (g)

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Quantitative Chemistry

• Calculating Masses
• The Mole
• Reacting Masses

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Calculating Masses

• Relative Atomic Mass
• This is the mass number that you find on the
  periodic table.
• Relative Molecular Mass
• This is the sum of all the
• relative atomic masses of all of the atoms in a
  compound e.g.

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The Mole

• One mole of atoms or molecule of any substance
  will have a mass in grams equal to the relative
  atomic mass or relative molecular mass for that
  substance.
• The atomic mass of carbon is 12, therefore one
  mole of carbon weighs 12g
• The relative molecular mass of oxygen (O2) is (2
  x 16) 23, therefore one mole of oxygen weighs
  32g.
• One mole of any substance contains 6.02 x 1023
  atoms or molecule.
• Remember the mole is just a number!

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Reacting Masses

• By using the relative molecular masses in grams
  we can deduce what masses of reactants to use and
  what mass of products will be formed.

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Changes to the Earth and Atmosphere

• 4.5 billion years ago
• When the Earth first formed, its surface was
  molten. As it cooled surface rocks formed. An
  atmosphere formed from volcanic gases carbon
  dioxide, steam, ammonia and methane.
• 3 billion years ago
• The Earth cooled enough for the steam to condense
  and form the oceans. The main gas in the
  atmosphere was carbon dioxide. Simple plants
  evolved.
• 2 billion years ago
• The first plant produced oxygen, this killed off
  many other life forms.
• 1 billion years ago
• The excess oxygen in the atmosphere reacted in
  the presence of UV light to form ozone. This
  ozone filtered out most of the damaging UV light
  and allowed more complicated life forms to
  evolve.
• The present time
• The atmosphere is approximately 1/5 oxygen and
  4/5 nitrogen.
• carbon dioxide is absorbed by plants, shellfish
  and dissolved in the oceans.
• It is given out by burning fuels, the decay of
  organic waste and released from volcanoes.
• ammonia in the air reacted with oxygen to form
  nitrogen. More nitrogen was formed by bacteria in
  the soil.

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The rock record
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Summary

• Useful Products from Oil
• Crude oil is a mixture of hydrocarbons. The can
  be separated and processed by cracking and
  polymerisation to make a variety of useful
  materials
• Useful Products from Metal Ores
• how we obtain metals depend on how reactive the
  are
• Useful Products from Rocks
• Limestone can be used as building material or as
  a raw material in cement, concrete and glass.
• Useful Products from Air
• Nitrogen from the atmosphere can be turned into
  synthetic fertiliser. Overuse cause
  eutrophication
• Representing Reactions
• practice balancing equations
• Quantitative Chemistry
• Practice lots of these problems.
• Changes to the Earth and Atmosphere
• The first atmosphere was mainly carbon dioxide.
  Plant produced all the oxygen in the atmosphere.
  This oxygen formed ozone which protects us from
  uv light.
• The Rock Record
• Rocks contain evidence of how they were formed.
  Different types of rock are linked in the rock
  cycle.