C6 - Electrolisis

Question 1

What does electrolisis mean?

Answer 1

It means splitting up with electricity

Question 2

What happens during electrolisis?

Answer 2

During electrolysis, an electric current is passed through an electrolyte (a molten or dissolved ionic
compound). The ions move towards the electrodes, where they react, and the compound decomposes.

Question 3

What happens to the positive ions in the electrolyte?

Answer 3

Positive ions in the electrolyte will move towards the cathode ( - electrode ) and gain electrons ( the ions are reduced )

Question 4

What happens to the negative ions in the electrolyte?

Answer 4

The negative ions will move towards the anode ( + electrode ) and loose electrons ( the ions become oxidised )

Question 5

In electrolisis what is the negative electeode called?

Answer 5

Cathode

Question 6

In electrolisis what is the positive electrode called?

Answer 6

Anode

Question 7

What causes a flow of charge in the elctrolyte?

Answer 7

When ions travel to the electrodes, it causes a flow of charge in the electrolyte

Question 8

What happens when he ions gain or loose electrons?

Answer 8

As ions gain or lose electrons, they form the uncharged element and are discharged from the electrolyte.

Question 9

What does electrolisis of molten ionic solids form?

Answer 9

Elements

Question 10

Why can an ionic solid not be electrolysed?

Answer 10

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

Question 11

Can molten ionic compounds be electrolysed and why?

Answer 11

Molten ionic compounds can be electrolysed because the ions can move freely and conduct electricity

Question 12

In electrolisis of molten ionic compounds what happens to the positive metal ions at the cathode and what happens to the negative non-metal ions at the anode?

Answer 12

Positive metal ions are reduced to the element at the cathode

Negative non-metal ions are oxidised to the element at the anode

Question 13

What are the uses of cryolite?

Answer 13

• Cryolite lowers the melting point
• So that less energy is used to melt the ore

Question 14

Explain the electrolysis extraction of Aluminium from the ore bauxite ( aluminium oxide Al2O3 )

Answer 14

• Aluminium oxide has a ver high melting temperature so it’s mixed with cryolite to lower the melting point.
• The positive Al3+ ions are attracted to the negative electrode where they each pick up three electrons and turn into neutral aluminum atoms. These then sink to the bottom of the electrolysis tank.
• The negative O2- ions are attracted to the positive electrode where they each lose two electrons.
  The neutral oxygen atoms will then combine to form O2 molecules.

Question 15

In electrolisis of an aqueous solution, as well as ions from the ionic compound there will be …… from the water

Answer 15

H+ ions and OH- ions

Question 16

At the negative electrode, if H+ ions are present, what will be produced if the metal ions form a metal that is more reactive than hydrogen or less reactive than hydrogen?

Answer 16

At the cathode, if H+ ions and metal ions are present, hydrogen pas will be produced
if the metal ions form an elemental metal that is more reactive than hydrogen
(e.g. sodium ions). If the metal ions form an elemental metal that is less reactive than
hydrogen (e.g. copper ions), a solid layer of the pure metal will be produced instead.

Question 17

At the positive electrode, if OH- ions and halide ions are present what happens? And what happens if the halide ions are not present?

Answer 17

At the anode, if OH- and halide ions (Cl-, Br-, I-) are present, molecules of chlorine, bromine or iodine will be formed.

If no halide ions are present, then the OH- ions are discharged and oxygen will be formed.

Question 18

What are the halide ions?

Answer 18

Cl- Br- I-
Chlorine, Bromine, Iodine