Electrolysis

Question 1

What is electrolysis

Answer 1

Electrolysis is the breakdown of a substance containing ions by electricity

Question 2

What types of ionic compounds cannot conduct electricity

Answer 2

Solid ionic compounds cannot conduct electricity. This is because the ions are locked in place by strong electrostatic forces of attraction, in the giant ionic lattice structure, and are not free to move

Question 3

what are the ions, in an ionic compound held in place by

Answer 3

Strong electrostatic forces of attraction

Question 4

Describe what happens when an ionic compound is melted or dissolved in water
Explain what this now means?

Answer 4

When an ionic compound is melted or dissolved in water, the forces of attraction are broken and the ions are free to move and carry a charge.

Because the ions can now move, these liquids and solutions can now conduct electricity. These liquids or solutions are called electrolytes

Question 5

In electrolysis what are the electrodes made from and why?

Answer 5

Graphite - conducts electricity and is inert (so it doesn’t react with the electrolyte)

Question 6

Negative electrode
Positive electrode
names

Answer 6

Negative electrode - Cathode
Positive electrode - Anode

Question 7

What is the cathode attached to

Answer 7

Cathode is attached to the negative terminal of the power pack/supply

Question 8

Cathode is covered with___

Answer 8

cathode is covered with electrodes which are coming from the power pack

Question 9

what is the anode connected to

Answer 9

Anode is connected to the positive terminal of the power pack/supply

Question 10

anode is not covered with___

Answer 10

Anode has a lack of electrons

Question 11

Describe what happens during the electrolysis of molten lead bromide

Answer 11

The positive lead (Pb2+) ions are attracted to the negative electrode (cathode) because opposite charges attract

At the cathode, the lead ions (Pb2+) gain two electrons to form Pb atoms (reduction)
(Pb2+ + 2e- —–> Pb)
Because lead ions are gaining electrons, lead ions are being reduced (an example of a reduction reaction)

The negative bromide ions (Br-) are attracted to the positive electrode (anode) because opposite charges attract

At the anode, the bromide ions (Br-) lose one electron to form Bromine atoms (oxidation)
(2Br- -2e- —-> Br2) - (br atoms pair to form a bromine molecule)

Because bromide ions are losing an electron, bromide ions are being oxidised (example of a oxidation reaction)

Question 12

how do you extract metals that are less reactive than carbon

Answer 12

Metals that are less reactive than carbon, can be extracted by reduction with carbon

Question 13

how do you extract metals that are more reactive than carbon

Answer 13

Metals that are more reactive than carbon, can be extracted by electrolysis

Question 14

how is aluminium extracted

Answer 14

aluminium is extracted from the compound aluminium oxide by (using) electrolysis

Question 15

Write the symbol equation for aluminium oxide

Answer 15

Al2O3

Question 16

Another name for aluminium oxide

Answer 16

Alumina

Question 17

What does aluminium oxide contain

Answer 17

It contains the aluminium ion (Al3+) and the oxide ion(O2-)

Question 18

Uses of aluminium

Answer 18

pans
drink cans
aeroplanes
overhead power cables
cooking foil
window and patio door frames
bicycle frames and car bodies

Question 19

Describe how aluminium is extracted by electrolysis

Answer 19

Aluminium is reduced (oxygen is removed) by decomposing it using electrolysis

For electricity to flow through the aluminium oxide, it must be molten (liquid)

Aluminium oxide has a very high melting point (around 2000 degrees celcius)

First, aluminium oxide is mixed with cryolite which lowers the melting point.

This reduces the amount of energy needed to melt the compound which saves money

Apply an electric current to the molten aluminium oxide.

The cathode and anode are both made of graphite (carbon) - it is a very good conductor of electricity, it has a very high melting point so it can be used at temperatures without melting

The aluminium ions (Al3+) and the Oxide ions (O2-) are free to move because this is molten aluminium oxide

The positive aluminium ions (Al3+ ions) are attracted to the cathode (the negative electrode) because opposite charges attract

At the cathode, each aluminium ion gains three electrons and forms an aluminium atom (this is reduction because aluminium ion has gained electrons - and reduction is the gain of electrons)

(these aluminium atoms sink to the bottom of the electrolysis tank)

Al3+ +3e- —–> Al

The negative oxide ions (O2- ions) are attracted to the positive electrode (anode)

At the anode, each oxide ion, loses two electrons to form an oxygen atoms (o2 gas molecules). because oxide ions are losing electrons, this is an example of oxidation reaction

Half equation to show the reaction at the anode: 2O2- -4e- —> 2O2

The anode must be replaced regularly.

Since the carbon (graphite) anodes are very hot they react with the oxygen molecules produced at the anode forming carbon dioxide gas

The carbon electrodes slowly burn away and so need replacing regularly.

C + O2 —> CO2

This is because the oxygen molecules produced at the anode react with the graphite (carbon) , forming carbon dioxide gas.

Question 20

Explain why producing metals by electrolysis is expensive

Answer 20

Melting the compounds such as aluminium oxide requires a lot of energy

A lot of energy is required to produce the electric current

Question 21

• explain why a mixture is used as the electrolyte - ELECTROLYSIS OF AL2O3

Answer 21

First, aluminium oxide is mixed with cryolite which lowers the melting point.

This reduces the amount of energy needed to melt the compound and saves money

Question 22

explain why the positive eletrode must be continually replaced - electrolysis of AL2O3

Answer 22

The anode must be replaced regularly.

Since the carbon (graphite) anodes are very hot they react with the oxygen molecules produced at the anode forming carbon dioxide gas

The carbon electrodes slowly burn away and so need replacing regularly.

Question 23

Write a half equation to show the reaction at the positive electrode

Answer 23

Anode - positive

2O2- - 4e- —> O2
2O2- ——> O2 + 4e -

Question 24

Write a half equation to show the reaction at the negative electdode

Answer 24

Al3+ + 3e- —-> Al

Question 25

Write the equation to show the reaction which causes the positive electrode to wear away

Answer 25

C + O2 —> CO2

Question 26

overall equation for electrolysis of aluminium oxide

Answer 26

Aluminium oxide -> aluminium + oxygen

2Al2O3(l) —> 4Al(l) + 3O2(g)

Question 27

why is aluminium expensive

Answer 27

High cost of electricity
Also high cost of heat and replacement electrodes

___________________
Melting the compounds such as aluminium oxide requires a lot of energy

A lot of energy is required to produce the electric current