0.1 M Sodium Thiosulfate Preparation as per USP
Introduction
Sodium thiosulfate is a versatile reagent used in various pharmaceutical and laboratory applications. The United States Pharmacopeia (USP) provides a standard method for the preparation of 0.1 M sodium thiosulfate solution, which is commonly used as a titrant in pharmaceutical analysis.
Preparation of 0.1 M Sodium Thiosulfate Solution
To prepare 0.1 M sodium thiosulfate solution, follow the steps outlined below:
Materials Required
- Sodium thiosulfate pentahydrate (Na2S2O3·5H2O)
- Distilled water
- Analytical balance
- Volumetric flask (1000 mL)
Procedure
- Weighing: Weigh accurately 25.0 grams of sodium thiosulfate pentahydrate (Na2S2O3·5H2O) using an analytical balance.
- Dissolution: Transfer the weighed sodium thiosulfate pentahydrate to a 1000 mL volumetric flask.
- Adding Water: Add about 500 mL of distilled water to the flask and swirl gently to dissolve the sodium thiosulfate pentahydrate.
- Dilution: Add more distilled water to the flask to bring the volume to 1000 mL. Mix well to ensure complete dissolution.
- Verification: Verify the concentration of the prepared solution by titrating it against a known concentration of potassium iodate (KIO3) solution.
Calculation of Molarity
The molarity of the prepared sodium thiosulfate solution can be calculated using the following formula:
Molarity (M) = Number of moles of sodium thiosulfate / Liter of solution
M = (25.0 g / 248.18 g/mol) / 1 L = 0.1 M
Storage and Stability
The prepared 0.1 M sodium thiosulfate solution should be stored in a cool, dark place. The solution is stable for at least 6 months when stored properly.
Conclusion
In conclusion, the preparation of 0.1 M sodium thiosulfate solution as per USP involves weighing and dissolving sodium thiosulfate pentahydrate in distilled water, followed by verification of the concentration through titration. The prepared solution is stable for at least 6 months when stored properly and can be used as a titrant in pharmaceutical analysis.
