Methyl orange (C14H14N3NaO3S) is an organic compound composed of nitrogen, carbon, sulfur hydrogen, oxygen, and sodium. It is an organic dye used as a pH indicator in titrations, because of its unique and diverse color variations at different pH levels.
Methyl Orange is an indicator used in acid-base titration which is known to shift color from red to orange-yellow in the range of pH of 3.1 to 4.4. This is due to the change in electrons and their arrangement when hydrogen ions are added and removed. When methyl orange becomes alkaline, a hydrogen ion is lost from the -NN- bridge between the rings.
The electrons that were once used to bind the hydrogen now neutralize the positive charge on the terminal nitrogen, preventing it from forming a pi bond. At endpoint this indicator turns from red to orange to yellow as the acidity of the solution decreases. If the solution becomes more acidic, the reverse is true.
According to modern benzenoid theory, pH indicators such as methyl orange exist in interchangeable forms, specifically the benzenoid and quinonoid structures. The theory states that one form predominates in one medium. The color of the Quinonoid form of the indicator is deeper than that of the Benzenoid form. Depending on the pH level, methyl orange can exist in either form.
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