S5 - Extraction and uses of metals (aluminium)

Question 1

Name the process used to extract aluminium?

Answer 1

Electrolysis

Question 2

Name the materials used for the electrodes

Answer 2

Graphite (carbon)

Question 3

What are the polarity of the two electrodes?

Answer 3

Anode = +
Cathode = -

Question 4

What are the two compounds present in the liquid?

Answer 4

Aluminium oxide (alumina) and cryolite

Question 5

What is the major cost of the attraction of aluminium?

Answer 5

Electricity

Question 6

What is the element at the anode?

Answer 6

Oxygen

Question 7

What is compound formed at the anode and explain how it forms.

Answer 7

Carbon dioxide - the oxygen produced at the anode combines with the carbon anode.

Question 8

Why is molten aluminium oxide difficult to obtain?

Answer 8

The melting point is extremely high.

Question 9

Give two reasons why cryolite is used in the electrolysis of aluminium oxide.

Answer 9

• to reduce the operating temperature of aluminium

- its a solvent

Question 10

Write the ionic half equation to show the formation of aluminium at the negative electrode (cathode)

Answer 10

Al3+ + 3e- —> Al

Question 11

Write the ionic half equation to show the formation of oxygen at the positive electrode (anode)

Answer 11

2O- - 4e- —> O2

Question 12

What type of process is the electrolysis of aluminium oxide?

Answer 12

Redox

Question 12

What is being oxidised in the the ionic half-equations out of the formation of aluminium and oxygen?

Answer 12

The oxides have been oxidised to oxygen molecules (loss electrons)

Question 13

What is being reduced in the the ionic half-equations out of the formation of aluminium and oxygen?

Answer 13

The aluminium ions have been reduced to aluminium atoms (gaining electrons)

Question 14

Why do positive electrodes (anode) need replacing regularly?

Answer 14

They are warn out because they are reacting with the oxygen in the air to form carbon dioxide
(C+O2 —> CO2)

Question 15

Describe the structure of aluminium

Answer 15

A lattice of Al+++ ions hold together by delocalised electrons.

Question 16

Why is aluminium a good conductor of electricity?

Answer 16

Delocalised electrons/ions can move freely around the structure with potential applied.

Question 17

What is the main ore of aluminium that is purified to make alumina?

Answer 17

Bauxite Al2O3

Question 18

Why doesn’t alumina powder conduct electricity?

Answer 18

The ions/electrons are stuck in the lattice unable to move freely.

Question 19

Why aluminium cannot be extracted using coke in a blast furnace?

Answer 19

Aluminium is more reactive than carbon. Carbon cannot remove the oxygen from the aluminium.

Question 20

What properties of aluminium are needed for the following:

Aeroplane bodies
Drink cans
Overheated power cables
Pans for cooking food

Answer 20

Aeroplane bodies - low density
Drink cans - malleable
Overheated power cables - conduct electricity
Pans for cooking food - conducts heat well

Question 21

What is meant by the term malleable?

Answer 21

Can be hammered into sheets

Question 22

Explain why aluminium is malleable

Answer 22

Layers of aluminium atoms that can slide past each other freely.

Question 23

What is meant by the term ductile?

Answer 23

Can be drawn out into wire

Question 24

What is meant by the term alloy?

Answer 24

Metals or non metals and metals mixed together.

Question 25

Give an example of an aluminium alloy and its use

Answer 25

Magnalium

To make aeroplanes bodies as they have a low density.

Question 26

Explain why the alloy is stronger than pure aluminium metal

Answer 26

In pure aluminium the atoms are all of the same size so the layers of atoms can slide past each other easily. The atoms of the metals alloyed with aluminium are of a different size. They therefore disrupt the lattice and stop the layers from sliding over each other.