Definition

Noun: - (Chemistry): A theory stating that all acid-base indicators are themselves either weak acids or weak bases. The key principle is that the ionized (dissociated) form of the indicator molecule has a different color than its non-ionized (undissociated) form. The color change observed during titration is due to a shift in the equilibrium between these two forms as the pH of the solution changes.

Usage Examples

• Noun:
  • Understanding the theory of indicators is essential for choosing the correct indicator for an acid-base titration.
  • According to the theory of indicators, phenolphthalein is colorless in its acidic (non-ionized) form and pink in its basic (ionized) form.
  • The experiment demonstrated the theory of indicators by showing how the color of methyl orange shifts from red to yellow as the solution becomes more basic.

Advanced Usage

• "Application of the theory of indicators": Refers to the practical use of this theory in analytical chemistry to determine titration endpoints.
  • The accurate determination of the equivalence point relies on the proper application of the theory of indicators.

Variants and Related Words

• Acid-base indicator (n): A substance that changes color depending on the pH of the solution it is in, operating on the principles described by the theory of indicators.
  • Litmus paper is a common acid-base indicator.
• Transition range (n): The narrow pH interval over which an indicator changes color, a concept explained by the theory of indicators.
  • An indicator's transition range should match the pH change at the equivalence point.

Synonyms

• Ostwald's theory of indicators: A specific name for this theory, attributed to the physical chemist Wilhelm Ostwald.
  • Ostwald's theory of indicators provides a quantitative explanation for the color change.

Noun

1. (chemistry) the theory that all indicators are either weak acids or weak bases in which the color of the ionized form is different from the color before dissociation