Chemistry / Unit 10 Chem 1865 short lesson, about 20 seconds
Acid-Base Indicators: Mechanism
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The idea
An acid-base indicator is a weak acid or base whose protonated and deprotonated forms differ visibly in color, so solution pH sets which color appears.
In practice
Methyl orange's protonated form appears red, its deprotonated form yellow, shifting as pH crosses its equilibrium.
Where people slip
An indicator changes color at its own equilibrium, not necessarily at a titration's equivalence point.
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