Phenolphthalein: Preparation, Properties and Applications

What is Phenolphthalein?

Phenolphthalein is an organic compound having the chemical formula C₂₀H₁₄O₄ that is used as a ㏗ indicator in acid-base titrations. So, as an indicator, it turns pink to red in alkaline and is colorless in acid solutions. In short, it can be written as 'HIn' or '㏗㏗'.

Structure of Phenolphthalein

Preparation of Phenolphthalein

Phenolphthalein can be synthesized by condensation of phthalic anhydride with two equivalents of phenol under acidic conditions.

Preparation of Phenolphthalein

Properties of Phenolphthalein

  1. Phenolphthalein is white-yellow, in its crystalline form.
  2. It is readily soluble in alcohols and mildly soluble in water.
  3. It does not have taste or smell and it is carcinogenic.
  4. It appears colorless till pH 8.5 and above that it appears as pink to deep red.

Applications of Phenolphthalein

  1. It is commonly used as an indicator in acid-base titrations. It turns colorless in acidic solutions and pink in basic solutions.
  2. It may be used as a laxative but it is not advisable due to the suspected carcinogenicity of this compound.
  3. It can be used in trap cases during anti-corruption operations as proof of acceptance of bribe. White-colored Phenolphthalein powder spread on currency notes and when any person touches it, the powder gets transferred to his hands. When his hands are washed with a colorless solution of sodium carbonate, it becomes immediately pink confirming the touching of currency notes.
  4. It is used to check the cement carbonation. If Phenolphthalein is applied to cement undergoing carbonation, it remains colorless (pH 8.5-9) whereas it turns pink when it is applied to normal cement. 


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