Download N4 Alloys Topic 9

Topic 9 – National 4 Chemistry Summary Notes
Metals and Alloys
Materials
LI 1
Materials are all substances and include:
metals
ceramics
plastics
natural substances novel substances.
Materials can be used for so many different jobs because of their
different properties. Some examples of materials and their uses are
shown in the table below.
Material
Use
Property/Properties
copper
electrical wiring
good conductor of
electricity
(metal)
porcelain
(fused with metal)
dental bridges
attractive
& strong
(ceramic)
poly(ethene)
washing-up bottles
(plastic)
penicillin
antibiotic
light
unreactive
durable i.e. long lasting
destroy bacteria
(natural substance)
Aluminium
aircraft
Strong & low density
(lightweight)
(metal)
The material we are going to look at most closely is metals.
LI 2
Reactivity of Metals
The Reactivity Series, which is shown in the table below, is a list which
places metals in order of their readiness to react. The most reactive
metals are at the top and the least reactive are at the bottom.
Metal
Potassium
Reactivity with
Oxygen
Reactivity with
water
react with
oxygen
react with water
Reactivity with
Acid
too reactive to
try in acid
Sodium
Calcium
Magnesium
react with acid
Aluminium
do not react
with water
Zinc
Iron
Nickel
only forms metal
oxide on the
surface of the
metal
Tin
Lead
Copper
do not react
with acid
Mercury
Silver
do not react
with oxygen
Gold
An easy way to remember The Reactivity Series is the following sentence:
Police Sergeant Charlie MAZINTL Caught Me Stealing Gold
i.e. P for potassium etc…
2
The general word equations if a metal can react with oxygen, water or
acid are given below.
Metal + Oxygen
metal + oxygen  metal oxide
e.g. magnesium + oxygen  magnesium oxide
Metal + Water
metal + water  metal hydroxide + hydrogen
e.g. potassium + water  potassium hydroxide + hydrogen
MAZINTL Metal + Acid
MAZINTL Metal + acid  salt + hydrogen
e.g. zinc + hydrochloric acid  zinc chloride + hydrogen
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LI 3
Extracting Metals
Less reactive metals can be found uncombined (not joined up with other
elements) in The Earth’s Crust and consequently were the first to be
discovered.
More reactive metals are always found combined and have to be
extracted (obtained) from ores. (see * below)
Metals have to be extracted from their ores by different methods. The
method used is shown in the table below and depends on the reactivity of
the metal.
Metal
Potassium
Sodium
Extraction Method
electrical energy
required
i.e. electrolysis
Calcium
*An ore is a compound of a
metal that occurs
naturally. For example, iron
oxide is iron ore.
Magnesium
Aluminium
Zinc
Iron
heat with carbon or
carbon monoxide
Nickel
Tin
Extracting a metal from
its ore is an example of a
reduction reaction.
Lead
Copper
Mercury
Silver
heat alone
Gold
4
The more reactive metals hold on more strongly to oxygen than the less
reactive metals. Therefore, it is much easier to remove oxygen from
compounds where it is joined to less reactive metals.
The most reactive metals hold on to oxygen more strongly than carbon
does. Heating with carbon or carbon monoxide therefore does not work.
Wars and the invention of electricity led to the large scale extraction of
more reactive metals.
The Blast Furnace
Iron is produced from iron ore in The Blast Furnace as shown in the
diagram below.
At the bottom of the furnace the reaction makes carbon dioxide
C + O2
CO2
Zone 1
Higher up, the carbon dioxide reacts with carbon to make carbon monoxide
CO2 + C
CO
Zone 2
Further up the carbon monoxide reacts with iron oxide to make iron and carbon
dioxide.
Fe2O3 + CO
Fe + CO2
Zone 3
5
Note: the limestone reacts with the impurities in the iron ore to form slag
LI 4
Corrosion
Corrosion is a chemical reaction which takes place on the surface of a
metal. The metal element changes into a compound. For example,
iron
(element)
+
oxygen

iron oxide
(compound)
For metals to corrode you need:
1. Water
2. Oxygen (from the air)
Not all metals corrode at the same rate. For example,

Gold corrodes so slowly that a piece of jewellery made in Egyptian
times is still as bright today!

Sodium corrodes so quickly that the formation of the oxide can be
seen happening
LI 5
Rusting
The corrosion of iron is called rusting.
During rusting the iron atoms initially lose two electrons to form Fe2+
ions.
i.e. Fe(s)

Fe2+(aq)
+
2e
(p.10 data book)
The electrons lost are accepted by the water and oxygen to from
hydroxide ions.
i.e.
2H2O(l)
+
O2(g)
+
4e

4OH-(aq)
(p.10 data book)
6
We can show that Fe2+ ions are produced during rusting by using ferroxyl
indicator.
Fe2+ ions turn yellow ferroxyl indicator blue – the more intense
the blue colour the more rusting has occurred.
Remember, whenever iron rusts OH- ions (hydroxide ions) are also
produced and these also have an effect on ferroxyl indicator.
OH- ions turn yellow ferroxyl indicator pink.
LI 6
Preventing Corrosion
Summary
The following prevent corrosion of a metal and are
explained in more depth below:

Coating

Galvanising

Connecting a metal to a more reactive metal
Coating
If oxygen and water can be kept from the surface of a metal, the metal
cannot corrode. Many surface barriers are used to prevent corrosion.

Coating with paint (metal fence), grease (bicycle chain) or plastic
(metal draining rack) protect iron objects – we say physical
protection is provided.

Coating with another metal ( see Galvanising)
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Galvanising
Galvanising – in this process the iron object is dipped into molten (liquid)
zinc. This stops oxygen and water from reaching the surface of the iron.
Even if the zinc coating is scratched it continues to protect the iron since
the electrons flow from the more reactive zinc on to the iron. For this
reason objects which take rough handling, such as wheelbarrows, are
often galvanised.
Sacrificial protection is a method for protecting a metal from corrosion
by attaching it to a metal which is higher up The Electrochemical
Series. ( similar to the Reactivity series, pg 10 of the data booklet)
In galvanising, both physical and sacrificial protection are provided.
Connecting A Metal To A More Reactive Metal
For a metal to corrode it must lose electrons. Connecting the metal to a
more reactive metal stops the metal losing electrons. Electrons flow from
the more reactive metal on to the metal preventing the loss of electrons
by the metal atoms.
Here are some examples,

Iron/Magnesium Cell
8

Ships have zinc plates bolted to their hull. Electrons flow from the
zinc on to the ship, slowing down the corrosion of the iron. Since
the zinc plates are losing electrons rapidly they have to be
replaced regularly.

Underground pipes are often connected to magnesium scraps. This
slows down the corrosion of the pipe since electrons flow from the
magnesium onto the pipe. Once again the scrap magnesium has to be
replaced regularly since it rapidly corrodes away.
These are examples of sacrificial protection.
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LI 7
Cells/Batteries
Note: whenever you see the word cell in these notes it can be replaced
with the word battery.
A cell is an arrangement which converts chemical energy into electrical
energy (electricity).
Electricity can be produced by connecting different metals together and
dipping them in an electrolyte (see note below) to form a cell.
Example – The Zinc/Copper Cell
The purpose of an electrolyte is to complete the circuit.
Note:

A solution or a molten compound which conducts electricity is
known as an electrolyte i.e. an ionic compound when in solution or
when molten.

Acids and ammonium chloride solution are examples of electrolytes.
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LI 8
The Electrochemical Series
We can use the equipment shown below to compare the voltage produced
by different pairs of metals sandwiched between an electrolyte.
The results obtained are given in the table below.
Metal Pair
Voltage Reading
(millivolts)
copper and copper
0
copper and tin
10
copper and iron
40
copper and zinc
50
copper and magnesium
60
copper and silver
-10
These results show that different pairs of metals give different voltages
and this leads to The Electrochemical Series which is shown on p.10 of
The Data Booklet.
The Electrochemical Series places metals in order of their ability to
supply electrons (it is very similar to The Reactivity Series but not
exactly the same) The metals at the top of The Series supply electrons
most easily.
Electrons always flow from the metal higher up The Electrochemical
Series to the metal lower down.
The further apart the metals are the higher the voltage they produce.
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LI 9
More Complicated Cells
The Zinc/Copper Cell Again!
In the above set-up:
Electrons flow from the zinc rod to the copper rod through the wires and
the meter.
Electrons always flow through the wires and the meter.
The purpose of the ion bridge is to complete the circuit – it is the
movement of ions in the ion bridge which completes the circuit.
Ions flow through the
ion bridge.
Electrons flow through wires.
Electrons always flow through the wires and meter from the metal higher up
The Electrochemical Series to the metal lower down.
When setting up a cell like the zinc/copper cell, for electricity to be
produced the metals have to be:
1. different
2. placed in a solution of their own metal ions. For example, zinc has
to be placed in a zinc…..solution, it cannot be placed in a
copper…..solution
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LI 10
Alloys
An alloy is a mixture of metals or of metals with non-metals.
An alloy has physical properties different to those of the elements from
which it is made. For example, pure gold is very soft, and if it was used to
make jewellery, it would soon wear away. Gold jewellery is actually made
from an alloy of gold and copper making it harder i.e. more wear resistant.
Some examples of alloys and their uses are shown in the table below.
Alloy
Elements Present
Use
brass
copper & zinc
door Hinges
iron, carbon, chromium
& nickel
cutlery
lead & tin
joins components to
circuit boards
Much harder than
either copper or zinc
stainless steel
The carbon causes the
iron to be less brittle.
The chromium & nickel
causes the iron to have
an increased
resistance to corrosion
solder
Melts more easily than
lead or tin
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Topic 9 Pupil Self Evaluation
Metals and Alloys – National 4
Number
Learning Intention
Success Criteria
I can:
1
I am going to find out about materials


give examples of materials and their uses
state the property/properties which are linked to these uses
2
I am going to find out about the
reactivity of metals


3
I am going to find out about extracting
metals from their ores


state the order of metals in The Reactivity Series
state if a metal reacts with oxygen, water or acid and write the
word equation for the reaction
state the definition of an ore
state the method of extraction required to extract a particular
metal from its ore
explain why this method of extraction is required
explain why unreactive metals were the first to be discovered
give examples of what led to the large scale extraction of the
more reactive metals
state which metal is produced in the blast furnace
state the reactions which take place in the blast furnace
state the definition of corrosion
the necessary conditions for metals to corrode
how the speed of corrosion of different metals compare



4
I am going to find out about corrosion





5
I am going to find out about rusting
6
I am going to find out about preventing
corrosion
I am going to find out about cells
7
8
I am going to find out about The
Electrochemical Series











9
10
I am going to find out about more
complicated cells
I am going to find out about alloys







state the metal that undergoes rusting
state the two equations involved in rusting
state the effect of ferroxyl indicator on Fe2+ and OH- ions
state ways of preventing corrosion, giving everyday examples
explain what happens in these processes
describe how electricity can be produced using metals
draw a set-up of how electricity can be produced using metals
state the purpose of an electrolyte
explain The Electrochemical Series
state the direction of electron flow if two different metals are
connected in a cell
relate the size of voltage produced to the position of metals in
The Electrochemical Series
draw a set-up of how electricity can be produced using metals
and solutions of their own ions
state where electrons flow in this set-up
state where ions flow in this set-up
state the purpose of an ion bridge
state the definition of an alloy
give examples of alloys and their uses
name the elements present in these alloys
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Topic 9 – Metals and Alloys Experiments – Nat 4
1. Materials - a selection of different materials - ??? – the ones
mentioned in the notes????
2. Reactivity of Metals


Alkali Metal demo
SGrade Topic 11 – Metals & Water/Acid/Oxygen - could test
for hydrogen if released.
3. Extraction of Metals - ??????????? do we have anything?
4. Corrosion – SGrade Topic 12 – nails expt in water etc…
5. Rusting – ferroxyl indicator and Fe2+ ion and OH- ion solutions
6. Preventing Corrosion – iron/magnesium cell set up in a u-tube with
salt water and ferroxyl indicator
7. Cells/Batteries






zinc rod
copper rod
dilute sulphuric acid
voltmeter
wires
lemon, wires, voltmeter, zinc & copper rods ?????????
8. The Electrochemical Series – SGrade Topic 10 Electrode Potential
9. The Zinc/Copper Cell Again!







zinc rod
copper rod
voltmeter
wires
filter paper
salt solution
zinc chloride solution

copper sulphate solution
10. Alloys


circuits boards
a selection of different alloys - ??? – the ones mentioned in
the notes????
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