Electrolysis
- When an electric current is passed through a molten or aqueous ionic compound the compound decomposes or breaks down
- Liquids and solutions that are able to conduct electricity are called electrolytes
- Covalent compounds cannot conduct electricity hence they do not undergo electrolysis
- An electrolytic cell is the name given to the set-up used in electrolysis and which consists of the following:
- Electrode: a rod of metal or graphite through which an electric current flows into or out of an electrolyte
- Electrolyte: ionic compound in molten or dissolved solution that conducts the electricity
- Anode: the positive electrode of an electrolysis cell
- Anion: negatively charged ion which is attracted to the anode
- Cathode: the negative electrode of an electrolysis cell
- Cation: positively charged ion which is attracted to the cathode
Diagram showing the direction of movement of electrons and ions in the electrolysis of NaCl
- During electrolysis the electrons move from the power supply towards the cathode
- Electron flow in electrochemistry thus occurs in alphabetical order as electrons flow from the anode to the cathode
- Positive ions within the electrolyte migrate towards the negatively charged electrode which is the cathode
- Negative ions within the electrolyte migrate towards the positively charged electrode which is the anode
Examiner Tip
When a metal conducts it is the electrons that are moving through the metal. When a salt solution conducts it is the ions in the solution that move towards the electrodes while carrying the electrons.
