What is the purpose of indicators in chemistry?

Indicators are substances that exhibit a distinct color change in response to changes in pH or specific ions in a solution. This color change occurs because indicators are often weak acids or bases themselves, and their chemical structure changes with the concentration of hydrogen ions (H+) in the solution, leading to different colors. For example, phenolphthalein turns from colorless in acidic solutions to pink in basic solutions, reflecting the changes in pH.

This property makes indicators especially useful in titrations and other types of acid-base chemistry, where monitoring the pH of a solution is crucial. Other choices do not accurately reflect the fundamental role of indicators in chemistry. Temperature-related color changes pertain to thermochromic substances, while detecting the presence of metals involves different chemical tests rather than indicators. Measuring volume pertains to volumetric analysis but does not relate to the functionality of indicators. Thus, the response that indicators change color in relation to pH or specific ions is the most accurate representation of their purpose in chemistry.