topic 4 - chemical changes: electrolysis

Question 1

What type of compounds are used in electrolysis?

Answer 1

Ionic.

Question 2

What happens when an ionic compound is melted or dissolved in water?

Answer 2

They are free to move around the solution.

Question 3

What is an electrolyte?

Answer 3

A molten or dissolved ionic compound which is able to conduct electricity.

Question 4

What are the two electrodes?

Answer 4

Anode and cathode.

Question 5

What happenns when you pass a current through an electrolyte?

Answer 5

The ions move to the electrodes.

Question 6

What is the anode?

Answer 6

The positively charged electrode.

Question 7

What is the cathode?

Answer 7

The negatively charged electrode.

Question 8

What is an anion?

Answer 8

A negatively charged ion.

Question 9

What is a cation?

Answer 9

A positively charged ion.

Question 10

Which electrode do positively charged ions move towards?

Answer 10

The cathode (the negatively charged electrode.

Question 11

Which electrode do negatively charged ions move towards?

Answer 11

The anode (the positively charged electrode.

Question 12

What happens when ions are discharged at the electrodes?

Answer 12

They produce elements.

Question 13

What do ions create when they travel to the electrodes?

Answer 13

A flow of charge through the electrolyte.

Question 14

Why can’t an ionic solid be electrolysed?

Answer 14

Because the ions are in fixed positions and can’t move.

Question 15

What are molten ionic liquids (e.g. lead bromide) always broken up into?

Answer 15

Their elements.

Question 16

In the electrolysis of molten ionic compounds, what is produced at the anode?

Answer 16

The non-metal.

Question 17

In the electrolysis of molten ionic compounds, what is produced at the cathode?

Answer 17

The metal.

Question 18

When is electrolysis used to extract metals from their ores?

Answer 18

When the metal is too reactive to be extracted by reduction with carbon or if the metal reacts with carbon.

Question 19

What is a disadvantage of extracting metals from their ores using electrolysis?

Answer 19

It is very expensive as lots of energy is needed to melt the compounds and produce the electrical current.

Question 20

How is aluminium manufactured?

Answer 20

By the electrolysis of a molten mixture of aluminium oxide and cryolite using carbon as the positive
electrode (anode).

Question 21

Why is a mixture used as the electrolyte in the extraction of aluminium?

Answer 21

To lower the melting point and therefore make it more cost-effective.

Question 22

Why must the positive anode be continually replaced in the extraction of aluminium?

Answer 22

The anode is made of carbon which reacts with oxygen to form carbon dioxide.

Question 23

When you electrolyse an aqueous solution, what else do you have to factor in?

Answer 23

The ions in the water.

Question 24

In the electrolysis of aqueous solutions, what is produced at the cathode if the metal is more reactive than hydrogen?

Answer 24

Hydrogen gas.

Question 25

In the electrolysis of aqueous solutions, what is produced at the cathode if the metal is less reactive than hydrogen?

Answer 25

A solid layer of the pure metal.

Question 26

In the electrolysis of aqueous solutions, what is produced at the anode if there are halide ions present?

Answer 26

Molecules of the halogen.

Question 27

In the electrolysis of aqueous solutions, what is produced at the anode if there are no halide ions present?

Answer 27

Oxygen.

Question 28

In an aqueous solution, what do the water molecules break down to produce?

Answer 28

Hydrogen ions and hydroxide ions.

Question 29

What type of reactions happen at the anode?

Answer 29

Oxidation reactions.

Question 30

What type of reactions happen at the cathode?

Answer 30

Reduction reactions.

Question 31

What can reactions at each electrode be represented by?

Answer 31

Half-equations.

Question 32

When combining/writing half-equations, what needs to be the same for each half-equation?

Answer 32

The number of electrons.