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MODEL RELEASED. Titration experiment. Student adding an indicator to a liquid in a conical flask during an acid-base titration experiment. This involves addition of an acid to a base, or vice-versa, with a burette (not shown) used to measure the volume of a known concentration added to a known volume in this conical flask. Colour changes in the indicator used show when the mixture has reached a neutral pH. This then allows known and measured volumes and the known concentration to be used in a calculation of the unknown concentration in the conical flask. The indicator used depends on the acid and base used. (KEYSTONE/SCIENCE PHOTO LIBRARY/SCIENCE PHOTO LIBRARY)