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Metals
and non-metals
Francine
Taylor-Campbell, Contributor
Important
information
- Metals
lose their valence electrons to
form a 'sea of electrons', which
are said to be delocalised. These
electrons are mobile and can bind
to the cations to form a strong
metallic bond.
- Non-metals
ionise by gaining electrons, thus
they are called oxidising agents.
- Non-metals
react with metals to form ionic
compounds and with other non-metals
to form covalent compounds.
- Metals
are mixed to form alloys in order
to improve certain physical properties
of the metals.
Examine
the questions below.
1.
Metals, both in the pure state and
as alloys, are used in the making
of many items. Give one use each for
copper and lead other than for making
containers. Give the physical property
that makes each metal suitable for
the use specified. (4 marks)
2.
For one named alloy of aluminium,
state the main constituents of the
alloy and give a reason for the use
of the alloy instead of the pure metal.
(3 marks)
3.
If you were provided with containers
made of the metals aluminium, zinc,
copper, magnesium and lead, state,
giving a reason in each case, which
one(s) would NOT be suitable for use
as cooking utensils, which ones would
be suitable to store sodium hydroxide
solution, a solution of iron (II)
sulphate and citrus juice. (9 marks)
4.
Describe the role of the following
metals; iron, magnesium and zinc in
living systems. (3 marks)
ANSWERS
1.
Copper is used to make electrical
cables as it is a good electrical
conductor. Lead is used to make the
protective shield to protect from
X-ray and radioactivity, as the radiation
cannot penetrate through the lead.
(2)
Magnalium is an alloy of aluminium
consisting of 70 per cent Al and 30
per cent Mg. It is used in the construction
of aircraft, as it is just as light
as aluminium but stronger and more
corrosion resistant than aluminium.
(3)
Magnesium and zinc would not make
suitable cooking utensils as they
would react with the solutions in
the containers and make people sick.
All the metals mentioned can be used
to store sodium hydroxide solution.
However, only copper and lead containers
could be used to store a solution
of iron (II) sulphate.
Comment:
Based on the reactivity of the metals,
none would be more reactive than sodium
so that it could displace it from
solution. Copper and lead are less
reactive than iron and would not be
able to displace it from solution.
Copper would be suitable to store
citrus juice.
Comment:
Citrus juice contains a weak acid
and only metals that would not react
with it could be used.
Iron
is an essential metallic element which
forms part of the haemoglobin structure
found in red blood cells. In plants,
it is also necessary for the formation
of chlorophyll.
Magnesium
is also an important component of
the chlorophyll molecule in plants.
Zinc
is a trace element needed for certain
enzymatic activities.
Question
2
Aluminium,
copper and iron are the most common
metals used in making cooking utensils.
Indicate the methods used for the
extraction of aluminium and iron and
give a reason, in each case, for the
use of that method.
Account
for the following:
a)
Certain types of foods cause pitting
(eating away of small areas of the
metal), especially in aluminium and
iron pots.
b)
In moist air, the surface of copper
pots first turns black very quickly
and then gradually goes green. Your
explanation must also include relevant
equations.
c)
Why is it likely to cost a householder
less money for electricity if rain
water is habitually used in an electric
kettle instead of tap water?
ANSWERS
To
extract aluminium, the molten ore
(bauxite - Al2O3.2H2O)
is electrolysed. This method is used
as aluminium is a reactive metal.
Reducing agents such as carbon or
carbon monoxide are reacted with the
ore (haematite - Fe2O3)
to extract iron. A less-powerful method
of reduction is used as iron is not
very reactive.
a)
The moisture and the weak acids in
these foods can react with the aluminium
and iron pots. This is usually referred
to as corrosion.
b)
The black colour on the copper is
due to the formation of copper oxide.
2Cu(s)
+ O2(g) == 2CuO(s)
The
change to a green colour is due to
the reaction between the copper oxide
and carbon dioxide in the atmosphere.
Note, the carbon dioxide in the moist
atmosphere could also react with the
water vapour to form the weak carbonic
acid (H2CO3).
CuO(s)
+ CO2(g) == CuCO3(s)
CuO(s)
+ H2CO3(aq)
== CuCO3(s) + H2O
(can be lost to the atmosphere)
c)
Rainwater is said to be soft as it
does not contain dissolved calcium
and magnesium ions which makes water
hard. Tap water is hard water and
when boiled, 'fur' which is CaCO3
and MgCO3, is deposited in the kettle.
This can eventually cause blockage
in the kettles and requires more energy
to bring the water to boil.
Francine
Taylor-Campbell is an independent
contributor.
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