Topic 9 – National 4 Chemistry Summary Notes

Metals and Alloys

Materials

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

(metal)

electrical wiring good conductor of

electricity

porcelain

(fused with metal)

(ceramic)

dental bridges attractive

& strong

poly(ethene)

(plastic)

washing-up bottles

light

unreactive

durable i.e. long lasting

penicillin

(natural substance)

antibiotic destroy bacteria

Aluminium

(metal)

aircraft Strong & low density

(lightweight)

The material we are going to look at most closely is metals.

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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 Reactivity with

Oxygen

Reactivity with

water

Reactivity with

Acid

Potassium

Sodium

Calcium

Magnesium

Aluminium

Zinc

Iron

Nickel

Tin

Lead

Copper

Mercury

Silver

Gold

react with

oxygen

only forms metal

oxide on the

surface of the

metal

do not react

with oxygen

react with water

do not react

with water

too reactive to

try in acid

react with acid

do not react

with acid

An easy way to remember The Reactivity Series is the following sentence:

i.e. P for potassium etc…

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Police Sergeant Charlie MAZINTL Caught Me Stealing Gold

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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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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 Extraction Method

Potassium

Sodium

Calcium

Magnesium

Aluminium

Zinc

Iron

Nickel

Tin

Lead

Copper

Mercury

Silver

Gold

electrical energy

required

i.e. electrolysis

heat with carbon or

carbon monoxide

heat alone

Extracting a metal from

its ore is an example of a

reduction reaction.

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*An ore is a compound of a

metal that occurs

naturally. For example, iron

oxide is iron ore.

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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

Note: the limestone reacts with the impurities in the iron ore to form slag

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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 + oxygen iron oxide

(element) (compound)

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

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)

For metals to corrode you need:

1. Water

2. Oxygen (from the air)

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We can show that Fe2+ ions are produced during rusting by using ferroxyl

indicator.

Remember, whenever iron rusts OH- ions (hydroxide ions) are also

produced and these also have an effect on ferroxyl indicator.

Preventing Corrosion

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)

Fe2+ ions turn yellow ferroxyl indicator blue – the more intense

the blue colour the more rusting has occurred.

OH- ions turn yellow ferroxyl indicator pink.

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

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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.

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

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)

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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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Cells/Batteries

Note: whenever you see the word cell in these notes it can be replaced

with the word battery.

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.

A cell is an arrangement which converts chemical energy into electrical

energy (electricity).

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The further apart the metals are the higher the voltage they produce.

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.

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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.

Ions flow through the Electrons flow through wires.

ion bridge.

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

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.

Electrons always flow through the wires and meter from the metal higher up

The Electrochemical Series to the metal lower down.

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Alloys

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

Much harder than

either copper or zinc

copper & zinc

door Hinges

stainless steel

The carbon causes the

iron to be less brittle.

The chromium & nickel

causes the iron to have

an increased

resistance to corrosion

iron, carbon, chromium

& nickel

cutlery

solder

Melts more easily than

lead or tin

lead & tin

joins components to

circuit boards

An alloy is a mixture of metals or of metals with non-metals.

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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

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

3 I am going to find out about extracting

metals from their ores

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

4 I am going to find out about corrosion state the definition of corrosion

the necessary conditions for metals to corrode

how the speed of corrosion of different metals compare

Topic 9 Pupil Self Evaluation

Metals and Alloys – National 4

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5 I am going to find out about rusting state the metal that undergoes rusting

state the two equations involved in rusting

state the effect of ferroxyl indicator on Fe2+ and OH- ions

6 I am going to find out about preventing

corrosion

state ways of preventing corrosion, giving everyday examples

explain what happens in these processes

7 I am going to find out about cells 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

8 I am going to find out about The

Electrochemical Series

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

9 I am going to find out about more

complicated cells

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

10 I am going to find out about alloys

state the definition of an alloy

give examples of alloys and their uses

name the elements present in these alloys

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

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copper sulphate solution

10. Alloys

circuits boards

a selection of different alloys - ??? – the ones mentioned in

the notes????