Definition

Noun: A chemical indicator that signals the completion of a reaction, specifically one involving the formation of a precipitate, by undergoing a distinct and observable change, typically in color. Its function is based on the principle of absorption, where it is adsorbed onto the surface of the newly formed solid particles.

Usage

An absorption indicator is used in analytical chemistry, particularly in titration experiments where the endpoint is marked by a precipitation reaction. The indicator itself changes color when it binds to the precipitate.

Examples

• In the Volhard method for chloride determination, ferric ion is used as an absorption indicator. The endpoint is signaled by the formation of a red-colored complex adsorbed on the silver chloride precipitate.
• The chemist added an absorption indicator to the solution before titrating, knowing its color change would clearly show when the precipitation was complete.
• Unlike acid-base indicators that change color in solution, an absorption indicator functions by attaching itself to the solid surface of the precipitate.

Advanced Usage

• Adsorption Indicator: This is a direct synonym and a more precise technical term for an absorption indicator, emphasizing the process of adsorption onto the precipitate's surface.
• The effectiveness of an absorption indicator depends on factors like the specific surface area of the precipitate and the ionic strength of the solution.

Variants and Related Words

• Adsorption Indicator (n): A synonym for absorption indicator.
• Precipitation Titration (n): A type of titration for which absorption indicators are commonly used.
• Endpoint Indicator (n): A general term for any substance that marks the endpoint of a titration; absorption indicators are a specific type.

Synonyms

• Adsorption indicator
• Precipitate indicator

Related Phrases

• To act as an absorption indicator: To function in the role of signaling a precipitation endpoint.
  • In this procedure, the dye eosin Y acts as an absorption indicator.

Noun

1. an indicator used in reactions that involve precipitation