Indicator is used to detect the end point of a titration by visual change of color. Indicators can be acid base indicator, precipitation titration indicator and redox indicators.
An acid base indicator shows different colors in acidic and basic media. So, in the absence of an acid base indicator the equivalence point can be determined by monitoring the changes in pH as the acid-base titration proceeds.
A precipitation indicator forms colored precipitate at the end point. In the absence of such indicators, the point where the formation of the precipitate just starts to take place is taken as the end point.
In a redox titration, the indicator used shows different colors in acidic and basic media. In the absence of redox indicator, usually one of the solution being titrated acts as a self indicator, like permanganate solution. So, there will not be any need to add an external indicator in such cases.
