4.3 Electrolysis

Question 1

What happens in the electrolysis of NaCl?

Answer 1

NaCl is dissolved or molten

Electrical current is passed through

NaCl separates into ions, Na is in group 1 therefore is an Na+ ion

Cl is in group 7 therefore is a Cl- ion

These ions then want to become neutral to reform elements

Na+ (as it is positively charged) will move to the negative electrode and regain an electron

Na+ + e- -> Na

Reforming the element Na

Cl- then moves to the positive electrode to donate an electron

2Cl- -> Cl2 + 2e-

Both elements are reformed, chlorine and sodium

Question 2

What is the process of electrolysis?

Answer 2

When an ionic compound is melted or dissolved

Ions are free to move throughout the liquid or solution

Ions are able to carry charge

A current is then passed through, so ions can move to the electrodes to then reform elements

Question 3

What are the positive and negative electrodes called?

Answer 3

Positive = Anode

Negative = Cathode

Question 4

When do we use electrolysis to extract pure metals?

Answer 4

When the metals are more reactive than carbon

They are too reactive to be extracted by reduction of carbon, so they are extracted by electrolysis instead

Question 5

Why is electrolysis an expensive process?

Answer 5

• Needs large amounts of energy to melt the metal compounds
• Needs large amounts of energy to produce the elctrical current

Question 6

How is aluminium manufactured?

Answer 6

Electrolysis of aluminium oxide and cryolite

Aluminium oxide has a very high melting point, its mixed with cryolite to reduce it so we dont need as much energy

Question 7

What type of equation is used to represent the reaction at an electrode?

Answer 7

Half equations e.g.

2Cl- -> Cl2 + 2e-