Determination of Chloride by Precipitation Titration with Silver Nitrate - Mohr's Method
This method determines the chloride ion concentration of a solution by titration with silver nitrate. As the silver nitrate solution is slowly added, a precipitate of silver chloride forms.
Ag+(aq) + Cl-(aq) --> AgCl(s)
The indicator used is dilute potassium chromate solution. When all the chloride ions have reacted, any excess silver nitrate added will react with chromate ions to form a red-brown precipitate of silver chromate. This procedure is known as Mohr’s method.
2Ag+(aq) + CrO42-(aq) --> Ag2CrO4(s)
The procedure described here for seawater may also be applied to water samples from various other sources to determine the relative concentrations of chloride ions in, e.g., stream water, river water, estuary water.
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Chloride Mohr (PDF 127Kb)
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