what color is methylene blue in the reduced state
Methylene blue Methylene blue is widely used as a redox indicator in analytical chemistry. Solutions of this substance are blue when in an oxidizing environment, but will turn colorless if exposed to a reducing agent. The redox properties can be seen in a classical demonstration of chemical kinetics in general chemistry, the "blue bottle" experiment. Typically, a solution is made of glucose (dextrose), methylene blue, and sodium hydroxide. Upon shaking the bottle, oxygen oxidizes methylene blue, and the solution turns blue. The dextrose will gradually reduce the methylene blue to its colorless, reduced form. Hence, when the dissolved dextrose is entirely consumed, the solution will turn blue again. The redox midpoint potential E0' is +0.011 mV.[36]
Acid–base titration Acid–base titration is performed with a bromothymol blue indicator, when it is a strong acid – strong base titration, a phenolphthalein indicator in weak acid – strong base reactions, and a methyl orange indicator for strong acid – weak base reactions. If the base is off the scale, i.e. a pH of >13.5, and the acid has a pH > 5.5, then an Alizarine yellow indicator may be used. On the other hand, if the acid is off the scale, i.e. a pH of <0.5, and the base has a pH < 8.5, then a Thymol Blue indicator may be used.