Name: China Factory Supply Best Price High Quality Phenolphthalein CAS 77-09-8
Brand: Wuhan Fortuna Chemical Co., Ltd.

Specifications of Phenolphthalein CAS 77-09-8

Items	Specifications	Results
Appearance	White or yellowish white crystalline powder	White crystalline powder
Related substances	≤0.5%	0.3%
Heavy metals	≤10ppm	Complies
Loss on drying	≤0.5%	0.1%
Sulphated Ash	≤0. 1%	0.02%
Assay	98.0%~101.0%	99.20%

Parameters of Phenolphthalein CAS 77-09-8

Product parameters
Cas number:	77-09-8
Appearance:	white or yellowish white crystalline powder
Purity:	98~101%
Package details:	25kg/drum
Brand:	Fortunachem

Phenolphthalein is a synthetic organic compound belonging to the phthalen dye family. It is most famous for its use as a pH indicator in acid-base titrations in chemistry. Its most recognizable property is its dramatic color change from colorless to a vivid fuchsia or pink color within a specific pH range.

Chemical Properties and How It Works

Phenolphthalein is a weak acid itself. Its color-changing ability stems from changes in its molecular structure as the pH of its environment changes.

In Highly Acidic and Neutral Solutions (pH < 8.3): The molecule exists in a "protonated" form. This form absorbs light in the ultraviolet spectrum, which is invisible to the human eye. Therefore, the solution appears colorless.
In Basic Solutions (pH ~ 8.3 - 10.0): As the solution becomes basic, the molecule loses protons (H⁺ ions) and undergoes a structural change. This new form absorbs light in the green region of the visible spectrum (~553 nm). Since green light is absorbed, we see the complementary color, which is a bright pink or magenta.
In Very Strongly Basic Solutions (pH > ~10.0), the color will fade and become colorless again as the molecule undergoes further structural change.

This makes it an ideal indicator for titrations where a strong base is added to a strong acid, as the endpoint occurs around pH 7-10, and the color change is sharp and unmistakable.

Primary Use: Acid-Base Indicator

This is its most common and iconic application:

Role: To provide a clear visual signal for the endpoint (the point of neutralization) in acid-base titrations.
Typical Scenario: It is famously used in titrations where a strong base (like sodium hydroxide, NaOH) is used to titrate a strong acid (like hydrochloric acid, HCl). A few drops of phenolphthalein are added to the acidic solution. As the base is added, the moment the solution turns a faint pink color that persists for 30 seconds, the endpoint has been reached.

Other Historical and Specialized Applications

Laxative: For much of the 20th century, phenolphthalein was a common active ingredient in over-the-counter laxatives (e.g., Ex-Lax). Its mechanism involved irritating the intestinal lining and stimulating bowel movements.

Important Note: Its use for this purpose has been banned or severely restricted in many countries (including by the FDA in 1999) due to concerns about potential carcinogenicity with long-term use.
Forensics - Blood Test: When reduced by a base and zinc dust, phenolphthalein turns pink in the presence of hydrogen peroxide and hemoglobin. This is the basis of the Kastle-Meyer test, a presumptive test for the presence of blood at crime scenes. A pink color indicates the likely presence of blood.
"Disappearing Ink": A classic toy and demonstration ink is made by dissolving phenolphthalein in alcohol and adding a base like sodium hydroxide to turn it pink. Blowing carbon dioxide (CO₂) from the air onto the drawing forms a weak acid (carbonic acid) that lowers the pH, making the color disappear.

Safety and Handling

Irritant: It is an irritant to the eyes and skin.
Health Risks: Its classification as a suspected carcinogen led to its removal from medicinal use. While the small amounts used in laboratory titrations are generally considered safe with proper handling, caution is still advised.
Always consult the Safety Data Sheet (SDS) for specific safety and handling instructions.

Summary

In essence, phenolphthalein is a classic pH indicator renowned for its clear colorless-to-pink transition around pH 8.3-10. While its historical use as a laxative is now obsolete due to safety concerns, it remains a fundamental tool in chemistry education and analytical labs for visualizing neutralization points and is still used in forensic science.