Phenolphthalein (CAS 77-09-8) is more than just a color-changing indicator; it’s a fascinating molecule whose chemical properties dictate its diverse applications. Understanding its structure, pKa, and reactivity is essential for scientists and chemists who rely on its performance. NINGBO INNO PHARMCHEM CO.,LTD., a leading manufacturer and supplier of fine chemicals, is pleased to share insights into the science behind this important compound.

Phenolphthalein, chemically known as 3,3-Bis(4-hydroxyphenyl)-1(3H)-isobenzofuranone, is a triphenylmethane dye. Its molecular formula is C20H14O4. The molecule’s structure contains two phenolic hydroxyl groups and a lactone ring. The distinctive pH-dependent color change is due to the opening and closing of this lactone ring and the subsequent changes in the molecule's conjugated system. In acidic to neutral solutions (pH < 8.3), the lactone ring is closed, and the molecule exists in its colorless H2In form. As the pH increases, the lactone ring opens, and the phenolic protons dissociate, forming the In2− species. This dianion has an extended conjugated system, which absorbs light in the visible spectrum, resulting in the characteristic pink color.

The pKa of Phenolphthalein is approximately 9.5, signifying the pH at which it is equally divided between its colorless and colored forms. This specific pKa range makes it ideal for titrating strong acids with strong bases, or weak acids with strong bases, where the equivalence point falls within this transition zone. However, it’s important to note that in very strongly basic solutions (pH > 13), Phenolphthalein undergoes a further reaction, forming a colorless carbinol compound, which can sometimes be mistaken for a weak acidic endpoint.

For professionals looking to buy Phenolphthalein, understanding these chemical behaviors is key to ensuring correct usage. NINGBO INNO PHARMCHEM CO.,LTD. provides high-purity Phenolphthalein, which guarantees consistent chemical properties and reliable performance. Our commitment as a manufacturer in China is to deliver products that meet the stringent demands of scientific research and industrial applications.

The ability to source quality Phenolphthalein from a reputable supplier like NINGBO INNO PHARMCHEM CO.,LTD. is crucial for consistent results. We offer competitive Phenolphthalein prices and ensure prompt delivery, making it easier for researchers and businesses to obtain the materials they need. Whether for analytical chemistry, material science, or educational purposes, our product is manufactured to the highest standards.

In summary, the scientific principles governing Phenolphthalein’s color change are rooted in its molecular structure and acid-base chemistry. A thorough understanding of these properties, coupled with sourcing from a reliable manufacturer like NINGBO INNO PHARMCHEM CO.,LTD., ensures that you can effectively utilize this versatile chemical in your work.