Acids and Bases- Disappearing Ink

  Disappearing Ink

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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