0.1 M Sodium Thiosulfate Preparation and Standardization
Introduction
Sodium thiosulfate (Na2S2O3) is a strong reducing agent commonly used in various analytical techniques, including titrimetry, spectrophotometry, and electrochemistry. In this article, we will discuss the preparation and standardization of 0.1 M sodium thiosulfate solution.
Preparation of 0.1 M Sodium Thiosulfate Solution
To prepare 0.1 M sodium thiosulfate solution, you will need:
- Sodium thiosulfate pentahydrate (Na2S2O3·5H2O)
- Distilled water
Procedure
- Weigh 24.82 g of sodium thiosulfate pentahydrate (Na2S2O3·5H2O) and transfer it to a 1 L volumetric flask.
- Add approximately 800 mL of distilled water to the flask and swirl to dissolve the solid.
- Add more distilled water to the flask until the mark is reached.
- Stir the solution well to ensure complete dissolution.
Standardization of 0.1 M Sodium Thiosulfate Solution
Standardization of the sodium thiosulfate solution is necessary to determine its exact concentration. This can be achieved by titrating the solution with a standard potassium bromate (KBrO3) solution.
Apparatus
- Burette
- Conical flask
- Magnetic stirrer
Procedure
- Weigh approximately 0.2 g of potassium bromate (KBrO3) and transfer it to a 250 mL conical flask.
- Add 50 mL of distilled water to the flask and swirl to dissolve the solid.
- Add 2-3 drops of methyl orange indicator to the flask.
- Titrate the potassium bromate solution with the prepared sodium thiosulfate solution until the color changes from yellow to colorless.
- Record the volume of sodium thiosulfate solution required to reach the endpoint.
Calculation
The concentration of the sodium thiosulfate solution can be calculated using the following equation:
Na2S2O3 (molarity) = (KBrO3 weight / KBrO3 molar mass) x (KBrO3 molarity / Na2S2O3 molarity)
where KBrO3 molar mass = 167.00 g/mol, KBrO3 molarity = 0.0167 M (assuming a 0.0167 M KBrO3 solution), and Na2S2O3 molarity = x.
Rearrange the equation to solve for x, the molarity of the sodium thiosulfate solution.
Tips and Precautions
- Handle sodium thiosulfate with care, as it can cause skin and eye irritation.
- Store the prepared solution in a cool, dark place to prevent degradation.
- Verify the concentration of the sodium thiosulfate solution regularly to ensure accuracy.
By following these steps, you can prepare and standardize a 0.1 M sodium thiosulfate solution for use in various analytical applications.
