MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY
Pupils performing a titration. Schoolgirl dripping measured volumes of an acid from a burette (down right), while a schoolboy takes notes. The conical flask (lower right) contains a measured volume of an alkali and the indicator methyl orange (from bottle at lower left). As the acid & alkali mix they change the pH of the solution, resulting in a change in the indicator's colour.
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