MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY
Acid-base titration. Image 3 of 3. Titrations are a method of volumetric analysis, in which a volume of one reagent is added to a known volume of another reagent until an end point. This end point can be measured by using an indicator, a substance that changes colour depending on its environment. This reaction is an acid-base titration, and the indicator used is methyl orange. The solution in the conical flask (bottom) has gone beyond the end point of pH 4.4, due to the addition of excess alkali from the burette (upper centre). The indicator is yellow here, showing it is more alkali. For a sequence showing the change in colour at the end point, see images A500/348-350.
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