metylorange

Metylorange, often spelled methyl orange in English, is a pH indicator used in acid-base titrations. It is an azo dye that changes color with acidity, appearing red in strongly acidic solutions and yellow in basic solutions. The name is used in several languages, where the spelling reflects regional conventions.

Chemically, metylorange is the sodium salt of 4-(dimethylamino)azobenzene-4'-sulfonic acid. In solution, the acid form is red and the deprotonated form is yellow, due to changes in the dye’s electronic structure. The color transition occurs over a narrow pH range, typically about 3.1 to 4.4, with a pKa around 3.4. Because of this, the indicator is most suitable for reactions that end in an acidic range.

Preparation and form: Metylorange is produced synthetically as an azo dye through diazotization and azo coupling, with the sodium salt being the common water-soluble form used in laboratories and industry. Its solutions are generally prepared at low concentrations (a few drops per titration) to observe the characteristic color change.

Applications: It is widely used for titrations where the end point lies in the acidic range, such as strong acid–weak base systems. It may also be used in certain food, water, or process testing scenarios. It is less suitable for strong acid–strong base titrations, for which indicators with higher pH transition ranges are preferred.

Storage and safety: Metylorange solutions should be stored in light-resistant containers, protected from excessive heat and oxidizers. It is handled with standard laboratory precautions; contact with skin or eyes should be minimized, and ingestion should be avoided.