C6

Question 1

Why do ionic compounds have to be melted or auqeous for electrolysis

Answer 1

When an ionic compound is melted or dissolved in water, the ions are free to move about within the liquid or solution.

Question 2

What is the electrolyte

Answer 2

The molten or aqueous ionic compounds that are able to conduct electricity in electrolysis

Question 3

What happens why lead bromide is electrolysed

Answer 3

When lead bromide is electrolysed in the molten state using inert electrodes:
Lead is produced at the cathode
Bromine is produced at the anode.

Question 4

Why do we extract certain metals using electrolysis

Answer 4

Electrolysis is used if the metal is too reactive to be extracted by reduction with carbon or if the metal reacts with carbon

Question 5

How is aluminium extracted

Answer 5

Aluminium oxide is found in the ore bauxite
The process includes molten mixture of aluminium oxide and cryolite ( catalyst to lower MP ) using carbon as the positive electrode (anode).

Question 6

Why is the positive electrode need to be replaced during the electrolysis of aluminium

Answer 6

Oxygen is discharged at the positive electrode. It reacts with the carbon to form carbon dioxide and slowly shrinks

Question 7

When electrolysing aqueous solutions what element is discharged at the negative electrode and why

Answer 7

At the cathode, hydrogen is produced if the metal is more reactive than hydrogen.

Question 8

When electrolysing aqueous solutions what element is discharged at the positive electrode and why

Answer 8

At the anode, oxygen is produced unless the solution contains halide ions when the halogen is produced.

Question 9

Why do the rules of the anode and cathode apply when electrolysis aqueous solutions

Answer 9

In the aqueous solution water molecules break down producing hydrogen ions and hydroxide ions that are discharged.

Question 10

What happens at the cathode in electrolysis

Answer 10

The cathode (negative electrode), positively charged ions gain electrons and so the reactions are reductions.

Question 11

What happens at the anode isn electrolysis

Answer 11

At the anode (positive electrode), negatively charged ions lose electrons and so the reactions are oxidations.

Question 12

What are the half equations for the electrolysis of aluminium

Answer 12

Cathode:
Al3+ + 3e- = Al

Anode
2O2- -4e- = O2

Question 13

What are the diagnostic tests for chlorine, oxygen and hydrogen

Answer 13

Chlorine: bleaches damp litmus paper
Oxygen: relights a glowing splint
Hydrogen: makes a squeaky pop with a lighted splint