What is Phenolphthalein?

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  • Written By: Felicia Dye
  • Edited By: C. Wilborn
  • Last Modified Date: 13 August 2019
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Phenolphthalein is a mild acid that can be used for medical and scientific purposes. When used in medicine, this compound is most commonly recognized as an ingredient in over-the-counter laxatives. In laboratory settings, it is typically used to test the acidity of other substances.

Phenolphthalein is a crystal powder that is usually white but may sometimes have a yellow tinge. It does not typically have a smell or a taste. It may, however, cause coughing or sneezing if it is inhaled.

This compound is often used for titration. This is a process in chemistry where a known amount of one chemical is used to cause a reaction that will reveal information about another chemical. When added to a solution for this sort of chemical testing, phenolphthalein is colorless. Phenolphthalein will not generally dissolve in water but it can be dissolved by alcohols such as ethanol and ether.

The solutions that contain phenolphthalein for chemical testing are therefore usually alcohol based. When the experiment begins, the liquid should be clear. If that solution is combined with a chemical that has a pH, or acidity rate, of about 8 or less, it typically remains without color.


If the solution is mixed with a substance that has an acidity rating from about 8 to 10, it can turn red or pink. If the acid levels of a substance exceed pH 10, the phenolphthalein solution can turn purple. When the acid levels move into the higher double digits, the solution typically becomes clear again. The color indication involved in this type of testing is typically described as a slow fading process.

Phenolphthalein has been used as a laxative for generations. There are growing concerns however that phenolphthalein may cause cancer in humans. These beliefs are typically driven by studies that were conducted on mice which developed tumors from exposure to the substance. These fears have resulted in many drug manufacturers replacing the substance with others that have laxative effects. The United States, for example, has seen a significant decline in its use.

This substance also has other uses that are not as commonly recognized. It can be used for blood tests in a process that typically also involves hydrogen peroxide. The substance can also be used in the manufacture of some toys.


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Post 1

Is it the same exact powder used in laxatives as in the laboratory? Or are there ingredients added for lab use?

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