Chemistry – Acids, bases and salts - Preparation of salts | e-Consult

To determine the concentration of chloride ions (Cl^-) in a water sample using precipitation, we can react the chloride ions with silver nitrate (AgNO₃) to form silver chloride (AgCl), which is an insoluble white precipitate. The reaction is:

Ag⁺(aq) + Cl^-(aq) → AgCl(s)

Reagents and Apparatus:

• Water sample
• Silver nitrate solution (AgNO₃) of known concentration
• Test tubes
• Droppers
• Beakers
• Pipettes (for accurate volume measurements)
• Filter paper
• Buchner funnel
• Drying oven

Procedure:

1. Using a pipette, accurately measure a known volume of the water sample and transfer it to a clean test tube.
2. Add a few drops of silver nitrate solution to the water sample in the test tube.
3. Observe the solution for the formation of a white precipitate. The formation of a precipitate indicates the presence of chloride ions.
4. If a precipitate forms, filter the solution through filter paper using a Buchner funnel to collect the solid silver chloride.
5. Wash the precipitate with distilled water to remove any remaining silver nitrate.
6. Dry the precipitate in a drying oven.
7. Weigh the dried silver chloride precipitate.

Interpretation of Results:

The mass of silver chloride formed is directly proportional to the number of chloride ions in the original water sample. The concentration of chloride ions can be calculated using the following equation:

Concentration of Cl^- = (Mass of AgCl / Molar mass of AgCl) / (Volume of water sample in dm³)

Where:

• Molar mass of AgCl = 143.32 g/mol
• Volume of water sample is in dm³ (convert from cm³ if necessary)