CHEM 2 Revision

This is for a GCSE standard for the AQA exam board. 

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  • Created on: 19-03-12 19:13
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Chem 2 Revision - Metals (Unit 2)
1. Basic ideas
Only less reactive metals such as gold, silver, copper and platinum are found uncombined in
the Earth's crust. We call these metals native metals.
Most metals are found as compounds with oxygen or sulphur in metal ores.
A metals ore is a rock from which it is economical to extract the metal. The factors that make
an ore economical are:
How easy it is to retrieve the metal.
The quantity of metal in the ore.
How much the metal is worth after extraction.
The Earth's crust contains metals and metal compounds such as gold, iron oxide and aluminium
oxide, but when found in the Earth these are often mixed with other substances. To become
useful, the metals have to be extracted from whatever they are mixed with. A metal ore is a
rock containing a metal, or a metal compound, in high enough concentration to make it
economic to extract the metal.
Ores are mined. They may need to be concentrated before the metal is extracted and
purified. The economics of using a particular ore may change over time. For example, as a
metal becomes rarer, an ore may be used when it was previously considered too expensive
to mine.
2. Ores of metals
Gold is found native (in its original form), like other unreactive metals. We call these lumps of
gold nuggets. On its own, gold is useless - it is extremely soft and will get damaged easily. It
is also densely packed, making it heavy.
All metals were formed in the Big Bang. When this occurred, the protons and neutrons
combined in different ways. Successful combinations formed elements.
Most metals are found in ores.
3. Mining
Mining is often quite a destructive activity, as it affects the population or habitats of wildlife,
causes pollution of groundwater and makes unsightly heaps of unused or wasted rock. For
local people, it brings business or jobs and expansion or money but the incoming miners may
also bring diseases to which the local people have little resistance.
Deep mining is costly and also very uncertain, as the veins of ores may be broken by faults of
rock. Mines may contain water which has to be pumped out. This makes deep mining very
expensive and risky for investors, though very profitable if a rich vein of ore is discovered.
Open-cast or surface mining, where the ore is scooped out by bulldozers is much cheaper
and also more predictable as it is much easier to be sure where the ore is, and no deep holes
have to be dug.
Deep mining and open-cast mining involve health risks to miners due to dust and sometimes
damp which may lead to lung diseases.
4. Phytomining
Phytomining involves the uses of plants which absorb metal ions from the soil through their
roots and concentrate the metals in their tissues. After harvesting, the plants are burned and
the metal is extracted from the ash, which is known as bio-ore. Metals such as gold,
palladium and thallium can be extracted this way. This method is used where it wouldn't
normally be worthwhile to extract the metal.

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Studies have now shown that using certain plants to extract metals from soil is commercially
feasible. These specially selected plants - called hyperaccumulators - are known for their
ability to take up through their roots and store particular metals. However, the plant has no
way of getting rid of the in-taken metal ions. Now a team of scientists has developed a nickel
hyperaccumulator for commercial use. This hay-like crop would be burned after harvest.…read more

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Gold, because it is so unreactive, is found as the native metal and not as a compound. It does
not need to be chemically extracted from its ore, but chemical reactions may be needed to
remove other elements that might contaminate the metal.
7.…read more

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Similarly, iron can be used to displace copper from copper sulphate solution. (Miners do this
by putting iron filings into a solution of copper minerals from copper mines.) This reaction can
be written as an ionic equation:
F e(s) + Cu2+(aq) F e2+(aq) + Cu(s)
The copper (II) ions have gained electrons. This is regarded as reduction.
The iron atoms have lost electrons. This is regarded as oxidation.
This can be remembered by the mnemonic OIL RIG; Oxidation Is Losing, Reduction Is Gaining.
10.…read more

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C aO + SiO2 CaSiO3
The main percentage of iron that leaves the blast
furnace in the impure iron is approximately 96%. The
other 4% is made up of impurities of which the main
one is carbon, but also includes silicon, sulphur,
phosphorus and manganese. These impurities get rid
of themselves. Sulphur reacts with added magnesium.
Oxygen gas is passed into the molten iron through a
tube called and oxygen lance. This is called a Basic
Oxygen Converter.…read more

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Pure metals are usually too soft to be very useful for most purposes, so we add other metals
or carbon to form alloys which have useful properties. The atoms of the other element
makes it more difficult for the metals cations to slide over one another and so the alloy is
usually stronger and harder than the pure metal.…read more

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Brass Zn 70% Harder than Copper. Corrosion resistant
Cu 30% screws, musical
Bronze Cu 90% Hard, strong, corrosion Statues, bearings.
Sn 10% resistant.
Cupro-nickel Cu 70% Hard, strong, corrosion `Silver' coins.
Ni 30% resistant.
Duralumin Al 94% Low density; higher Aircraft bodies.
Cu 4% strength/mass ration
Mg 1% than pure aluminium.
Titanium alloys Ti 90% Low density, strong, Hip replacements,
V 5% resistant to corrosion. parts of aircraft
Al 5% bodies, nuclear
reactors.…read more

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Smart alloys are shape memory alloys. If they are bent into another shape and then
reheated, they return to their original shape. They can be used to repair broken bones, or in
orthodontics to push teeth into the correct position. An example of a smart alloy is nitinol.
Smart alloys are alloys with a shape memory. Their technical name is shape memory alloys
(SMAs), which describes the way they behave - they seem to `remember' their original
shape.…read more

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T iO2 (2 ×O2-) + T i4+
First, it is made into titanium chloride. This is done by mixing it with carbon and heating it in a
furnace at 800oC. Then, chlorine gas is passed into the furnace, making titanium(IV) chloride
TiCl4 (gaseous at this current temperature) and carbon monoxide.
T iO2 + 2C + 2Cl2 T iCl4 + 2CO
Within the UK, they then displace the titanium from the chloride solution with molten sodium;
this results in titanium and sodium chloride.…read more

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It is therefore not attacked by air, water or acids at room temperature.
When molten, it reacts with carbon, oxygen and nitrogen, which makes it brittle.
Titanium has a much higher melting point than that of aluminium.
Metal Melting Point (oC)
Titanium 1660
Aluminium 660
Iron 1535
16. The hardness of steel
When iron comes out of the blast furnace it contains 10% carbon.…read more


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