Electrolysis of Solutions - GCSE Chemistry (Single Science) Revision
Overview
- Electrolysis: Process of using electricity to break down electrolytes to form elements.
- Applications: Purification of copper.
- Part of the Chemistry topic on Chemical Changes.
Basics of Electrolysis
- An electrolyte is a substance that conducts electricity when dissolved in water or molten.
- Electrolysis involves cathodes (negative electrodes) and anodes (positive electrodes).
Electrolysis of Water
- Ions in Water:
- Pure water conducts electricity due to dissociation into ions: hydrogen ions (H+) and hydroxide ions (OH−).
- Electrolysis Process:
- H+ ions move to the cathode, gain electrons to form hydrogen gas.
- OH− ions move to the anode, lose electrons to form oxygen gas.
- Balanced Equation: 2H2O(l) → 2H2(g) + O2(g)
- Gas Volumes: Hydrogen volume is twice that of oxygen.
Electrolysis of Aqueous Solutions
- Dissolved Ionic Compounds:
- Electrolytes contain positive ions (from water and compound) and negative ions (from water and compound).
- Ions compete at electrodes to gain or lose electrons.
At the Cathode
- Product Formation:
- If a metal is less reactive than hydrogen, the metal is produced.
- If a metal is more reactive, hydrogen is produced.
- Reactivity Series: Determines if hydrogen or metal appears at the cathode.
- Example: Potassium, sodium, calcium, magnesium, etc.
At the Anode
- Product Formation:
- Oxygen is typically produced unless halide ions are present.
- Halide ions (Cl−, Br−, I−) produce corresponding halogens (Cl2, Br2, I2) if present.
Examples of Products at Anode
| Negative Ion | Element at Anode |
|---|
| Chloride, Cl− | Chlorine, Cl2 |
| Bromide, Br− | Bromine, Br2 |
| Iodide, I− | Iodine, I2 |
| Sulfate, SO4²− | Oxygen, O2 |
Practical Example
- Electrolysis of Concentrated Sodium Chloride Solution: Chlorine is produced at the anode.
- Question: Predict product at positive electrode during electrolysis of concentrated sodium sulfate solution.
- Answer: Oxygen is produced.
Additional Resources
- Links to additional guides and revision resources on related topics such as acids, alkalis, and sample exam questions are available.
These notes summarize the key aspects of the electrolysis of solutions necessary for GCSE Chemistry revision, focusing on Edexcel specifications.