Electrolysis of Water
Description: A standard Hoffman apparatus demonstration. Voltage is applied to the system, and water is broken down into hydrogen and oxygen. The relative amount of each gas is 2:1. Bromothymol blue indicator is mixed into the solution. The solution turns blue (basic) on the side that hydrogen is produced, and yellow (acidic) on the side that oxygen is produced.
Source: Shakhashiri, B.Z. Chemical Demonstrations: A Handbook for Teachers of Chemistry
Year: 1991 Vol: 4 Page: 156
Keywords: Electrolysis, Hoffman apparatus, Acids, Bases, Indicators
Rating: 
Hazard: Some
- Electrocution hazard
- Flammability hazard
- Flammable gas-producing reaction
- Explosion hazard
Effectiveness: Average
- Good connection from demo to course material
- Results are observable with guidance
- Mild effects are seen by audience
- Time to results is high
- Good reliability
Difficulty: Medium
- Procedures with some intermediate steps to results
- Manipulations are simple for most to perform
- Use of scientific glassware
- Sequential or timed manipulations
- Prior training recommended
Safety Precautions:
- Eye protection required
- Perform in a well-ventilated area
- Use of UL approved three-prong plug and outlet required
- ABC fire extinguisher on hand
- Use caution when handling flammable gas
Class: Electrochemistry, Electrolysis, Acids and Bases
Division: General, Analytical Chemistry, Physical Chemistry
A different version of the demonstration Electrolysis of Water may be found under Stoichiometry- Electrolysis of Water.
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