Indicators and the End Point

The point where the indicator changes color is called the endpoint. Do not confuse the equivalence point with the end point. We usually choose an indicator whose range will cover the equivalence point. 

You can also monitor the pH with a pH meter. A pH meter is a concentration cell comparing the voltage difference between different concentrations of H+. (See Chemistry Lecture 7 for concentration cells.) 

You don t need to memorize this stuff about Indicators, but it s useful to understand. 

By Te way, von can remember that the end point is where the indicator changes color by spelling indicator as Endicator 

Since we established that the Hendefson-Hasseibaich equation is not useful to find the pH of the equivalence paint, how can it be useful to find an Indicator range that wili Include the equivalence point  

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Fe(III) can be titrated accurately with thiocyanate as an indicator if the reagent is added slowly near the end point or the temperature raised to 50 to 60°C. Dissolved air should be removed with a stream of carbon dioxide. Cu(II) can be titrated in the presence of thiocyanate to give a white precipitate of Cu(I) thiocyanate. Some Fe(II) is added as an indicator, and the end point detected by the disappearance of the red Fe(III)-thiocyanate color from the solution. Details for the determination of many oxidants (usually by adding an excess of Ti(III) and back-titrating with Fe(III), with thiocyanate as indicator) have been given. Potentiometric end points often are used. 

Ferric ammonium sulfate is used as the indicator, and the end point is located spectrophotometrically. 

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