Electrolysis of Halide Compounds
Chemistry: Cambridge International GCSE Supplement, topic 4.1.8
Electrolysis of Halide Compounds in Aqueous Solution
Electrolysis splits halide compounds in water, which predicts products at both electrodes.
What is the electrolysis of halide compounds?
- Electrolysis uses electricity to break down halide compounds dissolved in water.
- Halide compounds include salts like sodium chloride (NaCl) or potassium bromide (KBr).
- The solution contains halide ions (Cl⁻, Br⁻, I⁻) and water molecules (H₂O).
- Electrolysis splits ions into elements or new substances at electrodes.
Products at the positive electrode (anode)
- At the anode, negative halide ions lose electrons (are oxidised).
- Halide ions (Cl-, Br-, I-) produce halogen gases (Cl2, Br2, I2).
- If water is present in a dilute solution, halide ions oxidise first, unless they are absent.
- The halogen gas bubbles appear at the anode during electrolysis.
Products at the negative electrode (cathode)
- At the cathode, positive hydrogen ions (H+) or metal ions gain electrons (are reduced).
- In dilute solutions, H+ from water reduces to hydrogen gas (H2).
- Metal ions from halide salts (e.g. Na+, K+) usually stay in solution due to being very reactive.
- Hydrogen gas bubbles form at the cathode.
Effect of solution concentration
- In concentrated halide solutions, halide ions still discharge at the anode, producing halogen gas.
- At the cathode, hydrogen gas forms because metal ions of group 1 or 2 remain in solution.
- In dilute solutions, water ions mainly discharge at the anode and cathode.
- Concentration changes product proportions, but halogens appear at the anode.
Test yourself on Electrolysis of Halide Compounds
What is the purpose of electrolysis when applied to halide compounds dissolved in water?
Why do metal ions from Group 1 or 2 halide salts (e.g., Na⁺, K⁺) usually remain in solution at the cathode during electrolysis of dilute solutions?