Overview
This lecture covers the process and principles of electrolysis of molten binary ionic compounds, including the identification of products at each electrode and a worked example for molten potassium chloride.
Principles of Electrolysis of Molten Compounds
- A binary ionic compound contains two elements joined by ionic bonds.
- Electrolysis of molten compounds splits them into their element forms.
- To predict products, identify the ions present in the molten compound.
- Positive ions (cations) move to the cathode; negative ions (anions) move to the anode.
- The cathode always produces the metal, the anode always produces the non-metal.
Practical: Electrolysis of Molten Lead(II) Bromide
- Heat lead(II) bromide until molten to free the ions for conduction.
- Insert two graphite rods as electrodes and connect to a power supply.
- Turn on the power to start electrolysis.
- Negative bromide ions migrate to the anode, lose electrons, and form brown bromine gas.
- Positive lead ions migrate to the cathode, gain electrons, and deposit as grey lead metal.
Predicting Products: Worked Example
- For molten potassium chloride, ions present are K⁺ and Cl⁻.
- Chloride ions go to the anode and form chlorine gas.
- Potassium ions go to the cathode and form potassium metal.
Important Tips for Electrolysis Experiments
- Use inert electrodes (graphite or platinum) to prevent side reactions with the electrolyte.
Key Terms & Definitions
- Electrolysis — the splitting of a substance using electricity.
- Binary ionic compound — a compound containing two elements bonded ionically.
- Electrolyte — the molten or dissolved ionic compound undergoing electrolysis.
- Cathode — the negative electrode where reduction (gain of electrons) occurs.
- Anode — the positive electrode where oxidation (loss of electrons) occurs.
- Cation — a positively charged ion.
- Anion — a negatively charged ion.
- Inert electrode — an electrode that does not react during electrolysis.
Action Items / Next Steps
- Practice writing half-equations for reactions at cathode and anode.
- Complete related questions and exercises on electrolysis of molten compounds.