What type of solution is an indicator, characterized by a color change?

An indicator is a substance that typically changes color in response to a change in pH, which is often the result of the presence of acids or bases in a solution. The color change of the indicator helps to signal whether the solution is acidic, neutral, or basic.

Indicators are usually characterized as weak acids or weak bases because they exist in equilibrium between their protonated (acid form) and deprotonated (base form) states. This equilibrium allows them to produce a color change at specific pH levels. For instance, phenolphthalein is a common indicator that shifts from colorless in acidic solutions (pH < 7) to pink in basic solutions (pH > 8.2).

This characteristic of indicators – changing color at different pH levels due to their weak acid or alkali nature – is fundamental to their use in titrations and pH testing.