Electrolysis Flashcards
What happens in electrolysis?
- Electric current is passed through electrolyte
- Ions move to electrodes, forming pure elements
What is an electrolyte?
A liquid or solution that contains ions and so can conduct electricity
What are the electrodes?
Rods of metal or graphite through which an electric current flows into.
Why do solid ionic compounds not conduct electricity?
Ions cannot move
What must happen to solid ionic compounds before electrolysis?
Must be molten or dissolved
What are the positive metal ions attracted to?
The cathode
What is the cathode?
The negative electrode
What is the anode?
The positive electrode
What are the negative non-metal ions attracted to?
Anode
What happens at the anode?
Non-metals ions lose electrons -> become a pure non-metal
What happens at the cathode?
Metal ions gain electrons -> become a pure metal
What is different between the electrolysis of aqueous solutions and the electrolysis of molten compounds?
Aqueous: requires less energy, pure elements not always produced (due to isolation)
Electrolysis of solution: what is formed at the anode if the non-metal contains oxygen?
Oxygen
Electrolysis of solution: what is formed at the anode if the non-metal is a halogen?
The halogen gas
Electrolysis of solution: what is formed at the cathode if the metal is more reactive than hydrogen?
Hydrogen gas is formed
When is electrolysis used?
If the metal is more reactive than carbon
What happens before the electrolysis of aluminium oxide?
- Aluminium oxide is mixed with cryolite - lowers the melting point
- Mixture heated until molten
- Resulting molten mixture undergoes electrolysis
Electrolysis of aluminium oxide: what is formed at the cathode?
Pure aluminium
Electrolysis of aluminium oxide: what is formed at the anode?
Oxygen
Electrolysis of aluminium oxide: what is the anode made of?
Graphite
Electrolysis of aluminium oxide: what is a problem with the anode?
The graphite reacts with oxygen (to form carbon dioxide) so slowly wears away -> needs to be replaced frequently
Electrolysis of aluminium oxide: what is the molten mixture?
Aluminium oxide, cryolite
Electrolysis of aluminium oxide: what is the anode made of?
Carbon
How can we remember which electrode is which?
PANIC:
Positive
Anode
Negative
Is
Cathode
