Methyl Orange is a basic indicator that is employed in acid-base titration. In acidic conditions, it turns red, whereas, in basic conditions, it turns yellow. The indicator color change depends on the presence or loss of an ion. Methyl
orange indicator has a working pH range of 3.1 (red) and 4.4 (yellow).
The Quinonoid Theory of indicators states that every acid-base indicator exists in two tautomeric forms, the benzenoid form, and the quinonoid form. The two forms of colors are different. With a change in media, the concentrations of the two forms change.
Both forms have different colors. With a change in medium, the concentrations of the two forms change. Because they have different colors in different mediums, the medium changes as the color changes, giving us a suitable point to consider as a neutralization point.
The quinonoid form of methyl orange is red and is found mostly in acidic solutions, whereas the benzenoid form is yellow and is found primarily in basic solutions.
Below equilibrium is maintained by two forms.
As a result, the methyl orange indicator changes color since one of the above-mentioned structures was previously more dominant, but as the pH of the solution changes, the concentration of the other form increases while the concentration of the previous form decreases.
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