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Mohr’s Method | Determination of Concentration of Silver Nitrate

General Aim of Mohr’s Method

Determine the concentration of silver nitrate using the standard solution of sodium chloride.

 

Method of Mohr’s Method

Mohr’s Method.

Theoretical Background / Context

• Precipitimetry: It is a volumetric analysis method that involves the formation of a practically insoluble salt using a precipitating agent.
• Solubility product (Ksp): In a saturated solution of sparingly soluble electrolytes, the product of the molar concentration of ions each raised to a power equal to the number of ions produced is constant at room temperature and pressure.

Ksp of A_nB_m =[A]ⁿ[B]^m

N.B: Substance with low Ksp precipitate first.

Conditions required for a precipitimetry reactions:

1. The precipitate must be practically insoluble.
2. Rapid precipitation.
3. Ease of detection of the endpoint.

Principle Work of Mohr’s Method

• Mohr’s method is a direct argentometric titration (silver nitrate titration) used for quantitative chemical analysis.
• In a neutral or slightly alkaline medium, sodium chloride is titrated with silver nitrate (AgNO3) forming silver chloride precipitate using n-chromate as a Mohr method indicator.

NaCl + AgNO3NaNO3 +AgCl

• After precipitation of all chloride, the first drop excess of AgNO3 will react with n-chromate forming:

Ag2CrO4 reddish-brown precipitate in Mohr’s titration. (endpoint