acid-base indicator

A pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH (acidity or alkalinity) of the solution can be determined easily. Hence a pH indicator is a chemical detector for hydronium ions (H3O+) (or Hydrogen ions (H+) in the Arrhenius model). Normally, the indicator causes the colour of the solution to change depending on the pH. pH values above 7.0 are basic, and pH values below 7.0 are acidic. Solutions with a pH value of 7.0 are neutral. Most pH values range from 1 to 14, but superacids may have a negative pH value. Similarly, superbases may have pH values greater than 14.
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Noun
1. an indicator that changes color on going from acidic to basic solutions
(hypernym) indicator
(hyponym) phenolphthalein

A weak acid that has acid and base forms with sharply different colors. Changes in pH around the acid's pKa are "indicated" by color changes.

B: (Kimia) indikator asam-basa
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