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Methyl red (2-(N,N-dimethyl-4-aminophenyl) azobenzenecarboxylic acid) , also called C.I. Acid Red 2, is an indicator dye that turns red in acidic solutions.It is an azo dye, and is a dark red crystalline powder. Methyl red is a pH indicator; it is red in pH under 4.4, yellow in pH over 6.2, and orange in between, with a pKa of 5.1.ethyl red (2-(N,N-dimethyl-4-aminophenyl) azobenzenecarboxylic acid) , also called C.I. Acid Red 2, is an indicator dye that turns red in acidic solutions.
For litmus, it so happens that the 50 / 50 colour does occur at close to pH 7 - that's why litmus is commonly used to test for acids and alkalis. As you will see below, that isn't true for other indicators. Methyl orange. Methyl orange is one of the indicators commonly used in titrations. In an alkaline solution, methyl orange is yellow and the structure is: Now, you might think that when you add an acid, the hydrogen ion would be picked up by the negatively charged oxygen. That's the obvious place for it to go.