Methylorange

Methyl orange is a pH indicator dye used in acid–base chemistry. It is the water-soluble sodium salt of a sulfonated azobenzene, typically described as the disodium salt of p-dimethylaminoazobenzenesulfonic acid.

Its color depends on pH: in strongly acidic solutions it appears red, while in basic solutions it turns yellow. The transition occurs over a narrow range, approximately pH 3.1 to 4.4, making it suitable for detecting the end point of certain acid–base titrations.

Preparation and structure: Methyl orange is a synthetic azo dye produced by diazotization of an amine followed by azo coupling, yielding the sulfonated dye that dissolves in water. The common form used in laboratories is the disodium salt.

Applications: It is widely used as an indicator for titrations involving strong acids with weak bases (for example, HCl with ammonia) where the end point occurs below pH 4. It is less suitable for titrations involving strong bases or very strong acids. It is also used in analytical chemistry and colorimetric tests requiring a red-to-yellow color change in the acidic range.

Safety and handling: As a synthetic dye, methyl orange can act as a skin and eye irritant and should be handled with appropriate precautions. It is not used as a food additive and should be disposed of according to regular laboratory waste procedures.