Indicator

This is the substance that forms precipitates, changing color or other parameters, when the concentration of the solute component in the solution changes. These are weak acids or bases, whose molecular (undissociated) form is characterized by one color, while the ionized form has a different color. For example, methyl orange, methyl red, phenolphthalein.

Source | Glossary of Most Commonly Used Biomedical Terms and Concepts | Lithuanian University of Health Sciences | Academician Professor Antanas Praškevičius, Professor Laima Ivanovienė