Disappearing Ink
In the first photo, a hand tilts a bottle with blue liquid over a white cloth, and a blue area appears on the cloth. In the second photo, the white cloth shows no blue stain.
Description: Basic thymolphthalein indicator solution is blue but changes to colorless at about pH 10. The solution is sprayed on cloth, and a “stain” appears. After 5 minutes, the stain fades due to the absorption of carbon dioxide from the atmosphere.
Source: Institute for Chemical Education Fun With Chemistry: A Guidebook of k-12 Activities Vol.1
Year: 1991 Vol: 1 Page: 91
Keywords: Thymolphthalein, Carbon dioxide, Spray, Acid, Base
Rating: 
Hazard: Some
- Corrosive to metals
- Acute toxicity hazard
- Skin corrosion hazard
- Eye irritation
Effectiveness: Average
- Mild effects are seen by audience
- Connected conceptually to course material
- Good reliability
- Time to results is high
- Observable with guidance
Difficulty: Low
- Simple adding of reagents
- Simple procedures
- Simple manipulations
Safety Precautions:
- Eye protection required
- Gloves required
- Absorbent material on hand
- Perform on a chemically resistant surface
Class: Acids and Bases, Indicators
Division: General
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