Phenolphthalein - C20H14O4

What is Phenolphthalein?

Phenolphthalein is an organic compound which is used medicinally as a cathartic. It has a chemical formula C20H14O4. It is written as “phph” or  HIn”. It is used in acid base titration as an indicator. As an indicator it turn pink to red in alkaline and is colorless in acid solutions. It is dissolved with alcohol for experiment purpose and it is slightly soluble in water. It is either yellowish-white to pale orange or white fine crystalline powder and in its liquid form it appears as a colorless till PH 8.5 and above that it appears as pink to deep red. It does not have taste and smell. This chemical compound is widely used as PH indicator and laboratory agent. Under acidic conditions when phthalic anhydride is condensed with two  equivalents of pheno, Phenolphthalein is synthesized. It is a weak acid and belong to class of dyes called Pthalein dyes

Properties of Phenolphthalein – C20H14O4

C20H14O4 Phenolphthalein
Molecular Weight/ Molar Mass 318.32 g/mol
Density 1.277 g/cm3
Appears White powder
Melting Point 258–263 °C

Phenolphthalein structure – C20H14O4


C20H14O4 Uses (Phenolphthalein)

  • It is used in acid base titrations as an indicator
  • It is used in Kastle-Meyer test
  • It was before used as a laxative

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Practise This Question

Assertion – The non-fusible impurities present in iron ore are removed by CaCO3 .

Reason: CaCO3 which decomposes into CaO and CO2. The CaO formed reacts with SiO2 to remove silica