An acid-base indicatior is a compound who's color is pH dependent. That is, it changes color depending upon whether it is in acid or base. This is because indicators are weak acids and undergo the following equilibrium. H-Ind ↔ H+1 + Ind-1 H-Ind = the indicator molecule that is protonated and predominates under acidic conditions. Ind-1 = the deprotonated indicator molecule (the conjugate base of the acid) and predominates under basic conditions. We are using the Acid-Base indicator, phenopthalein for this experiment. What is the color of this indicator in Acid? . What is the color of this indicator in Base

Substances called indicators are those whose solutions change colour as the pH changes. We refer to these as acid-base indicators. The conjugate base or acid versions of these typically weak acids or bases have various hues because of variations in their absorption spectra. When it comes into contact with an object that has a pH of 8.2, it turns pink. At a pH higher than that, it turns purple.

Additionally, ionisation, which modifies the charge and structure of the phenolphthalein molecule, is the cause of this shift in colour. If it comes into contact with an acid like vinegar or a neutral substance like water, it retains its colorlessness.

Therefore, Phenolphthalein is pink in acid and colorles in base.

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