MODEL RELEASED. Titration experiment. Schoolgirl adding acid (from a burette) to neutralize a known volume of an alkaline solution (in conical flask). The alkalinity is indicated by the phenolphthalein indicator (from the bottle). This indicator turns pink in an alkaline solution and colourless in an acidic solution. The burette is graduated to show volumes, and this allows measurement of the volume of acid used to turn the solution colourless. This volume of acid is compared to the known volume of alkali, giving information on reaction chemistry and chemical concentrations.