Limit test for Chloride

• The limit test for chloride is a qualitative test that detects whether the concentration of chloride ions (Cl⁻) in a sample is below a predefined acceptable limit.

• It is based on the principle of a precipitation reaction between silver ions (Ag⁺) and chloride ions (Cl⁻), resulting in the formation of an insoluble white precipitate of silver chloride (AgCl).

Chemical Reaction

Ag+ (aq) + Cl- (aq) → AgCl (s)

Procedure of Limit test for Chloride

1) Preparation of Reference Standard Solution

• Prepare a reference standard solution with a known concentration of chloride ions, usually from sodium chloride (NaCl) or potassium chloride (KCl).

• This standard represents the acceptable limit of chloride ions.

2) Preparation of Test Solution

• Prepare a test solution from the sample to be analyzed, ensuring any chloride ions present are in a soluble form.

3) Addition of Silver Nitrate (AgNO₃)

• Add equal volumes of silver nitrate solution to both the test solution and the reference standard solution.

• The silver nitrate provides the silver ions for the reaction.

• Ensure the concentration of AgNO₃ is slightly in excess to react fully with chloride ions.

4) Acidification with Dilute Nitric Acid (HNO₃)

• Add dilute nitric acid to both solutions to prevent the precipitation of other silver salts that could interfere with the test results.

5) Observation of Precipitate

• Look for the formation of a white precipitate of silver chloride (AgCl) in both the test and reference solutions, indicating the presence of chloride ions.

6) Comparison of Precipitate

• Compare the turbidity or intensity of the precipitate in the test solution with the reference standard solution.

• If the test solution's precipitate is less intense or less turbid than the reference solution, the chloride concentration is below the acceptable limit.