Explaining Conductivity — Electrolysis | IGCSE Chemistry

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 7% of your exam marks.

stable

Low

Stable7%

Electrode products, half-equations and OILRIG tested in most series.

An electric current is a flow of charged particles
- In a metal wire the moving charges are electrons
- In a molten or aqueous ionic substance the moving charges are ions
Most covalent compounds have no charged particles that are free to move, so they do not conduct
This makes them useful as electrical insulators in a wide range of forms
- Solid: the plastic sheathing on household wiring (poly(ethene), PVC)
- Liquid: silicone oils inside transformer cores
- Gas: sulfur hexafluoride (SF₆) inside high-voltage switchgear

In the solid state, the ions sit in fixed positions within the giant ionic lattice and cannot move past one another, so the solid does not conduct
In the molten state, the lattice has broken down and the ions are free to move and carry charge through the liquid
In aqueous solution, the water separates the ions from each other and the dissolved ions are again free to move and carry charge
An ionic substance set up so that current can pass through it is called the electrolyte

A cation is a positively charged ion (Na⁺, Mg²⁺, H⁺)
An anion is a negatively charged ion (Cl⁻, O²⁻, SO₄²⁻)
In an electrolysis cell, two electrodes dip into the electrolyte and are connected to a d.c. supply
- The cathode is the negative electrode
- The anode is the positive electrode
Once the supply is switched on, the ions migrate toward the oppositely charged electrode
- Cations move to the cathode
- Anions move to the anode
Electrons flow in the external wire from the anode to the cathode, completing the circuit