phenolphthalein

Thân thiện

A scientist adds phenolphthalein to a clear solution, turning it bright pink.

Definition

1. Noun:
   • A chemical compound used primarily as a laxative in medicinal preparations.
   • A chemical compound used as an acid-base indicator in laboratory titrations, turning from colorless in acidic or neutral solutions (below pH 8) to a brilliant red or pink color in basic solutions (above pH 8).

Usage

• As a Laxative: Phenolphthalein was historically a common ingredient in over-the-counter laxative medicines.
  • Example: The doctor advised against using products containing phenolphthalein for long-term constipation relief.
• As a Laboratory Indicator: In chemistry, phenolphthalein is used to visually detect the endpoint of a titration, specifically when a weak acid is neutralized by a strong base.
  • Example: We added two drops of phenolphthalein to the flask; the solution remained colorless until the base was added, at which point it turned pink.

Advanced Usage

• Chemical Properties: Phenolphthalein's color change is reversible. If an acid is added to the red basic solution, it will become colorless again.
  • Example: The pink color of the phenolphthalein faded when we added a few drops of hydrochloric acid.

Variants and Related Words

• Indicator (n): A substance that changes color to show the presence or condition of another substance, such as acidity or alkalinity.
• Titration (n): An analytical laboratory technique to determine the concentration of an unknown solution by reacting it with a solution of known concentration.

Synonyms

• Laxative agent (for its medicinal use).
• Acid-base indicator (for its laboratory use).

Related Phrases/Idioms

• To act as an indicator: To serve as a sign or measure of something. (This is a general phrase, not specific to phenolphthalein).
  • Example: Economic growth can act as an indicator of a country's overall health.

Học thuật

Noun

1. a laxative used in many preparations under various trade names; also used as an acid-base indicator in titrations involving weak acids and strong bases because it is brilliant red at high alkalinity and colorless below pH 8