Assay of Sodium Chloride by Precipitation Titration
Aim: To perform the assay of sodium chloride by precipitation titration.
Requirements:
- Apparatus: Beaker, Funnel, Pipette, Burrette,
- Chemicals: Sodium chloride, Ammonium thiocyanate.
Procedure:
(A) Standardisation of Ammonium thiocyanate, 1 M: Solutions of any molarity 1 M may be prepared by dissolving 76.12 g in sufficient water to produce 1000 ml.
Procedure: 30 ml of silver nitrate solution (0.1 M) mixed with 50 ml of water. Add 2 ml of nitric acid and 2 ml of ferric ammonium sulphate. Titrate with ammonium thiocyanate solution.
An endpoint is a red-brown colour.
N1V1 = N2V2
Normality of silver nitrate solution × Volume of silver nitrate solution = Normality of ammonium thiocyanate solution × Volume of ammonium thiocyanate solution.
(B) Assay: Weigh accurately about 0.1 g and dissolve in 50 ml of water in a glass-stoppered flask. Add 50.0 ml of 0.1 M silver nitrate, 5 ml of 2 M nitric acid and 2 ml of dibutyl phthalate, shake well and titrate with 0.1 M ammonium thiocyanate using 2 ml of ferric ammonium sulphate solution as an indicator, until the colour becomes reddish yellow.
1 ml of 0.1 M silver nitrate is equivalent to 0.005844 g of NaCl.
Observation table: (Standardization)
| Sr. No. | Parameters | Reading |
| 1. | Burette solution | Ammonium thiocyanate solution |
| 2. | Conical flask solution | Silver nitrate |
| 3. | Indicator | Ferric ammonium sulphate |
| 4. | Endpoint | Formation of precipitate |
| Burette reading B.R (ml) | Trial 1 | Trial 2 | Trial 3 | Average (BR) |
Observation table: (Assay)
| Sr. No. | Parameters | Reading |
| 1. | Burette solution | Ammonium thiocyanate |
| 2. | Conical flask solution | Nitric acid, dibutyl phthalate |
| 3. | Indicator | Ferric ammonium sulphate |
| 4. | Endpoint | Reddish yellow (precipitate) |
| Burette reading B.R (ml) | Trial 1 | Trial 2 | Trial 3 | Average (BR) |
Result: The % purity of sodium chloride is …….
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