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Titration experiment to measure the volume of acid needed to neutralize an alkaline solution. The alkaline solution is in the conical flask (bottom centre) and its alkalinity is indicated by the use of phenolphthalein indicator from the bottle. This indicator turns pink in an alkaline solution and colourless in an acidic solution. The acid is in the burette, the volume-measuring apparatus held over the flask. The tap (lower centre) is used to add acid until a colourless solution forms at the reaction endpoint. This acid volume is compared to the known volume of alkali, giving information on reaction chemistry and chemical concentrations. (KEYSTONE/SCIENCE PHOTO LIBRARY/ANDREW LAMBERT PHOTOGRAPHY)