Description: Basic thymolphthalein indicator solution is blue, but changes to colorless at about pH 10. The solution is sprayed on a cloth, and a "stain" appears. After 5 minutes, the stain fades due to absorption of carbon dioxide from the atomosphere.

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Source: Institute for Chemical Education Fun With Chemistry; A Guidebook of K-12 Activities. vol 1

Year or vol: 1991 page: 91

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