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Mansoura National University
Pharm D-Clinical Pharmacy Program Level 1 Pharm. Anal. Chem. 1 (PC 101)
Detection of the End Point in Argentometric Titrations
• Many methods are utilized in determining the end point in these titrations, but we
will mention only the most important ones:
A) Using indicator methods:
1. Formation of secondary colored precipitate at E.P. (Mohr's method) [more]
2. Formation of soluble colored complex at E.P. (Volhard’s method) [folhard]
3. Adsorption indicator method. (Fajans’ method) [fayans]
B) No indicator method
- Appearance of ppt. at E.P. (Turbidimetric method)
(Liebeg’s method and its modification)
1. Mohr’s Method
➢ It is a type of argentometric precipitation titration that depends on
Principle the formation of a colored secondary precipitate at the end
point
- - - -
Used for ➢ Used for the determination of Cl and Br (Not for I or SCN ).
Type of titration ➢ Direct titration.
pH ➢ Done in Neutral or slightly alkaline medium (pH ≈ 6.5 -9).
➢ soluble chromate salt, Na CrO or K CrO , used as 5% solution
Indicator 2 4 2 4
(yellow solution)
➢ formation of a secondary-colored precipitate;
Detection of ➢ Ag CrO ppt. is brick red in color, so a color change is observed
endpoint 2 4
at the endpoint as darkening of the yellow chromate color.
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