Using the Formaldehyde Clock Reaction to Show How Buffers Work
Description: A mixture containing a 10:1 molar ratio of HSO3– : SO32- is prepared. It has a pH of approximately 6. When formaldehyde is added to the solution, the bisulfate is consumed but not the sulfite. The pH changes as the ratio of bisulfite to sulfite changes. The change is pH is monitored by phenolphthalien indicator and by graphing the pH on a computer.
Source: Harris, David C. Quanitative Chemical Analysis
Year: 1999 Vol: N/A Page: 228
Keywords: Clock reactions, Buffers, Acids and Bases, Sulfites, Graph
Rating: 
Hazards: Medium
- Acute toxicity hazard – oral, inhalation, dermal
- Flammable liquids
- Skin corrosion hazard
- Serious eye damage
- Skin sensitization
- Germ cell mutagenicity
- Carcinogenicity
- Reproductive toxicity hazard
- Specific organ toxicity – single exposure – central nervous system, respiratory system
- Short term aquatic toxicity
Effectiveness: Average
- Somewhat connected to course material
- Time to results is medium
- Secondary effects
- Mild effects are seen by audience
- Moderate reliability
Difficulty: Medium
- Some sequential manipulations
- Procedures with some intermediate steps to results
- Use of scientific instruments
- Experiments in which a display is used
Safety Precautions:
- Eye protection and gloves required
- Avoid exposure to droplets, mists, and vapors
- Perform in a well-ventilated area
- Use UL approved three-prong plug and outlet
- Prevent release of reagents to the environment
- Absorbent materials on hand
- Sodium bicarbonate on hand
- ABC fire extinguisher required
Class: Clock Reactions, Buffers
Division: Analytical
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