What is an acid–base indicator? Define the equivalence (stoichiometric) point and the endpoint of a titration. Why should you choose an indicator so that the two points coincide? Do the pH values of the two points have to be within 60.01 pH unit of each other? Explain. Why does an indicator change from its acid color to its base color over a range of pH values? In general, when do color changes start to occur for indicators? Can the indicator thymol blue contain only a single — CO2H group and no other acidic or basic functional group? Explain.