Titration. Potassium permanganate (purple) being added, from a burette, to a known volume of iron (II) solution, in a flask. This is the end point of the reaction. As the potassium permanganate reacts with the iron it becomes colourless. At the end point there are no more iron ions for the potassium permanganate to react with, and so the last drop retains its colour. The burette is graduated to show volumes, allowing the volume of the potassium permanganate added to the iron to be measured. The volume of potassium permanganate is compared to the known volume of iron, giving information on reaction chemistry and chemical concentrations.