Electrolysis

Question 1

4.4.3.1

Why does a substance need to be molten or aq to undergo electrolysis?

Answer 1

Because then the ions are free to move around within the solution. These liquids / solutions can conduct electricity and are called electrolytes

Question 2

4.4.3.1

What’s an electrolyte?

Answer 2

The solution / molten substance that undergoes electrolysis

Question 3

4.4.3.1

What does passing an electric current through the electrolyte do?

Answer 3

Causes the ions to move yo the electrodes

Question 4

4.4.3.1

What’s the negative electrode called?

Answer 4

Cathode

Question 5

4.4.3.1

What’s the positive electrode called?

Answer 5

Anode

Question 6

4.4.3.1

Where do negative ions move to?

Answer 6

Positive electrode

Anode

Question 7

4.4.3.1

Where do the positive ions move to?

Answer 7

Negative electrode

Cathode

Question 8

4.4.3.1

What’s electrolysis?

Answer 8

The splitting of a compound (ionic) using electricity.

Question 9

4.4.3.2

What type of substance is formed at the Cathode

Answer 9

The cathode is negative so it attracts positively charged ions
Metals

Question 10

4.4.3.2

What type of substance is formed at the Anode

Answer 10

The anode is positive so it attracts negatively charged ions
Non-metals

Question 11

4.4.3.3

When is electrolysis used?

Answer 11

When the metal is too reactive to be extracted by reduction with carbon
OR
when the metal reacts with carbon (rare that metals react with carbon)

Question 12

4.4.3.3

How can metals be extracted?

Answer 12

From a molten compound by electrolysis

Question 13

4.4.3.3

Why is electrolysis expensive?

Answer 13

Because large amounts of energy are used to melt the compound
AND
Because large amounts of energy are used to produce electrical current

Question 14

4.4.3.3

What substance is added to Al2O3 to lower the melting point?

Answer 14

Cryolite

Question 15

4.4.3.3

What forms at the anode / cathode from aluminium oxide?

Answer 15

Cathode : aluminium

Anode : oxygen

Question 16

4.4.3.3

Why do the electrodes need to be replaced during electrolysis of aluminium oxide (Al2O3)?

Answer 16

Because the oxygen formed at the anode (positive electrode) reacts with the carbon so it must be continually replaced.

Question 17

4.4.3.4

What happens to the ions at the electrodes

Answer 17

They get discharged

Question 18

4.4.3.4

When is hydrogen produces at the cathode?

Answer 18

In an AQ solution when the metal is MORE reactive than hydrogen

This is because in the AQ solution water molecules break down produces H+ ions

Question 19

4.4.3.4

When is oxygen produced at the anode?

Answer 19

In an AQ solution When halide ions / halogens are not present

This is because in the AQ solution water molecules break down produces OH-ions

Question 20

4.4.3.5

What type of reaction occurs at the anode?

Answer 20

The negative ions lose electrons

OXIDATION

Question 21

4.4.3.5

What type of reaction occurs at the cathode?

Answer 21

The positive ions gain electrons

REDUCTION

Question 22

4.4.3.5

Half equation for hydrogen

Answer 22

2H+ + 2e- —> H2

Question 23

4.4.3.5

Half equation for Hydroxide

Answer 23

4OH- - 4e- —> O2 + 2H2O