Phenolphthalein丨CAS 77-09-8

1. pH Indicator in Acid-Base Titrations

Phenolphthalein is one of the most widely used acid-base indicators in laboratories:

Color change range: pH 8.2 (colorless) to 10.0 (bright pink)

Commonly used in alkalinity tests, titrations, and water hardness analysis

Used in educational settings to demonstrate acid–base reactions

2. Analytical Chemistry

Functions as a tracer in various chemical analyses

Employed in complexometric titrations involving EDTA to determine metal ion concentrations

3. Medical Use (Historically)

Laxative use (formerly): Once widely used as an over-the-counter stimulant laxative due to its ability to stimulate bowel movements

Now largely discontinued for medicinal purposes in many countries due to carcinogenicity concerns found in long-term animal studies

4. Forensic Science

Used in latent blood detection (phenolphthalein test or Kastle–Meyer test):

Reacts with hemoglobin in blood in the presence of hydrogen peroxide, producing a pink color

Valuable for preliminary forensic screening at crime scenes

5. Polymer and Plastics Industry

Used as a component in pH-sensitive polymers, especially in hydrogels and smart materials

Acts as a model compound in polymer degradation and diffusion studies

Highly Visible Color Change: Its sharp and distinct color transition makes it a preferred indicator for many titrations.

Stability: Phenolphthalein is stable in dry form and has a long shelf life under proper storage conditions.

Sensitivity: Detects even small changes in pH, particularly in basic environments.

Multi-Disciplinary Utility: It serves in academic, medical, forensic, and industrial settings, demonstrating its versatility.