Electrolysis breaks an ionic compound down using electricity
Definition
Electrolysis
The decomposition of an ionic compound, when molten or in solution, by passing an electric current through it.
Definition
Electrolyte
A molten or dissolved ionic compound that conducts electricity and is broken down during electrolysis.
- Electrolysis uses an electric current to break an ionic compound down into simpler substances.
- The compound being broken down is the electrolyte.
- An electrolyte conducts electricity only when it is molten or dissolved, because its ions are then free to move.
- A solid ionic compound does not conduct, because its ions are locked in a fixed lattice.
Key Idea
- A current can only flow when the ions are free to move and carry the charge.
- Melting or dissolving the compound frees the ions from the lattice.
Ions move to the oppositely charged electrode
Definition
Cathode
The negative electrode during electrolysis, where positively charged ions gain electrons.
Definition
Anode
The positive electrode during electrolysis, where negatively charged ions lose electrons.
- Two electrodes dip into the electrolyte and are connected to a power supply.
- The cathode is the negative electrode and the anode is the positive electrode.
- Positive ions (cations) are attracted to the negative cathode.
- Negative ions (anions) are attracted to the positive anode.
Note
- Opposite charges attract, so each ion moves to the electrode with the opposite charge.
- This steady movement of ions is what carries the current through the electrolyte.
At the electrodes, ions are discharged into elements
Definition
Discharge
The gain or loss of electrons by an ion at an electrode, turning it into a neutral atom or molecule.
- At the cathode, positive ions gain electrons and are discharged as neutral atoms.
- At the anode, negative ions lose electrons and are discharged as neutral atoms or molecules.
- These discharged particles are the elements that make up the compound.
- Because the compound is split into its elements, electrolysis is a decomposition reaction.
Self review
- What is an electrolyte?
- Why must an ionic compound be molten or dissolved before it can be electrolysed?
- Which ions move to the cathode, and why?
- What happens to a positive ion when it is discharged at the cathode?
- Why is electrolysis described as a decomposition reaction?
