Assay of Sodium Benzoate by Non Aqueous Titration
Aim: To perform the assay of sodium benzoate by non-aqueous titration.
Requirements:
- Apparatus: Beaker, Funnel, Pipette, Burette.
- Chemicals: Sodium benzoate, Perchloric acid, KHP.
Monograph: Sodium benzoate.
- Chemical Formula: NaC7H5O2.
- Molecular Weight: 144.1.
- Sodium benzoate contains not less than 99.0 per cent and not more than 100.5 per cent of NaC7H5O2, calculated on a dried basis.
- Category: Pharmaceutical acid (preservative).
- Description: A white, crystalline or granular powder or flakes; odourless or with a faint odour; hygroscopic.
Procedure:
(A) Standardisation of Perchloric acid, 1 M: Solutions of any molarity of 1 M may be prepared by diluting 82 ml of perchloric acid to 1000 ml with water.
Procedure: Weigh 0.7 gm of KHP, dissolve in 50 ml of acetic acid. Add 2 drops of crystal violet and titrate with perchloric acid. Colour changes from blue to green. Subtract the volume of perchloric acid consumed by 50 ml of acetic acid.
1 ml perchloric acid is equivalent to 20.42 mg of KHP.
(B) Assay: Weigh accurately about 0.25 g, dissolve in 20 ml of anhydrous glacial acetic acid, warming to 50°C necessary, cool. Titrate with 0.1 M perchloric acid, using 0.05 ml of 1-naphtholbenzene in solution as an indicator. Carry out a blank titration.
1 ml of 0.1 M perchloric acid is equivalent to 0.01441 g of NaC7H5O2.
Observation table: (Standardization)
| Sr. No. | Parameters | Reading |
| 1. | Burette solution | Perchloric acid |
| 2. | Conical flask solution | KHP |
| 3. | Indicator | Crystal Violet |
| 4. | Endpoint | Blue to Green |
| Burette reading B.R (ml) | Trial 1 | Trial 2 | Trial 3 | Average (BR) |
Observation table: (Assay)
| Sr. No. | Parameters | Reading |
| 1. | Burette solution | Perchloric acid |
| 2. | Conical flask solution | Sodium benzoate |
| 3. | Indicator | Naphtholbenzein |
| 4. | Endpoint | Change in colour |
| Burette reading B.R (ml) | Trial 1 | Trial 2 | Trial 3 | Average (BR) |
Result: The % purity of sodium benzoate is …….
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