C3.4 Electrolysis

Question 1

What is electrolysis?

Answer 1

Electrolysis is a process in which an electric current is passed through a compound, causing a chemical change.

Question 2

How does electroplating work?

Answer 2

During electroplating, metal ions from the electrolyte are discharged on the surface of the object (cathode). These ions are replaced by metal ions leaving the surface of the anode. Overall, metal leaves the anode and is deposited on the object. The process continues until the anode is used up.

Question 4

What three complements do you need for electrolysis to work?

Answer 4

An electrolyte - a compound in its liquid state or in solution, which contains mobile ions and conducts electricity.
Two electrodes - made from a metal or graphite, which conduct electricity to the electrolyte
An electric supply such as a power pack or battery

Question 5

What is an anode?

Answer 5

A positively charged electrode

Question 6

How can you test if hydrogen is produced?

Answer 6

Hydrogen makes a ‘squeaky pop’ when burnt with a lighted splint

Question 8

What happens at the cathode?

Answer 8

Positive metal ions are reduced to atoms at the cathode

Question 9

In an aqueous solution, at the cathode if hydrogen ions and metal ions are present…

Answer 9

Hydrogen gas will be produced if the metal is more reactive than hydrogen. If the metal is less reactive than hydrogen then a solid layer of the pure metal will be produced instead.

Question 10

In an aqueous, at the anode if halide ions are present…

Answer 10

Molecules of halogen elements will be formed. If no halide ions are present then oxygen will be formed from the hydroxide ions

Question 11

How can you test if chlorine is produced?

Answer 11

Chlorine bleaches damp litmus paper so it goes white because solution of chlorine is acidic.

Question 12

What are inert electrodes?

Answer 12

Inert electrodes are made from unreactive metals. They are not changed during electrolysis.
Inert electrodes can be used for the electrolysis of many ionic compounds in their liquid state or in aqueous solution.

Question 13

What happens during the electrolysis of water?

Answer 13

Water is naturally partially ionised
Contains small concentrations of hydrogen ions and hydroxide ions
During electrolysis, hydrogen ions are discharged at the cathode as hydrogen in its gas state and hydroxide ions are discharged at the anode framing water and oxygen in its gas state.

Question 15

List the reactive series of metals with hydrogen shown for comparison from most reactive to least reactive

Answer 15

Potassium
Sodium
Calcium
Magnesium
Aluminium
Zinc
Iron
Tin
Lead 
(hydrogen)
Copper
Silver
Gold
Platinum

Question 16

Give examples of inert electrodes

Answer 16

Platinum

Carbon

Question 17

What is electroplating?

Answer 17

Electroplating is a type of electrolysis that uses non-inert electrodes

Question 18

What are non-inert electrodes?

Answer 18

Non-inert electrodes change during electrolysis

They react

Question 19

In electroplating what is the cathode, anode and electrolyte?

Answer 19

Cathode - object you want to coat
Anode - piece of metal you want to coat the object with
Electrolyte - solution containing ions of the coating metal

Question 20

Electroplating

As the reaction continues…

Answer 20

…the mass of the anode will decrease and the mass of the cathode will increase because the ions are transferred from the anode to the cathode.

Question 21

Surfing electroplating with silver what happens at the anode and at the cathode?

Answer 21

At the anode silver atoms lose electrons to become ions

Silver ions gain electrons at the cathode to become an atom.

Question 23

How is copper purified?

Answer 23

Copper is purified in a similar way to electroplating, except both electrodes are made from copper. The anode is impure copper and the cathode is very pure copper. Copper(II)sulphate solution is commonly used as the electrolyte. During electrolysis, the cathode gains copper atoms and increases in mass, while the anode loses copper atoms and decreases in mass. Impurities from the anode fall off and collect underneath it.

Question 25

What happens at the anode?

Answer 25

The negative ions are oxidised to atoms at the anode.

Question 28

What are cations?

Answer 28

Positive ions

Question 34

What are anions?

Answer 34

Negative ions

Question 42

What is a cathode?

Answer 42

The negatively charged electrode