硫代硫酸钠滴定液的标定流程图内容英语
    ## Standardization of Sodium Thiosulfate Solution.
    ### Introduction.
    Sodium thiosulfate is a versatile reagent used in various analytical applications, including iodometric titrations. The accuracy of these titrations relies on the precise standardization of the sodium thiosulfate solution. This article provides a comprehensive guide to the standardization process, explaining the principles, steps, and calculations involved.
    ### Principle.
    The standardization of sodium thiosulfate solution involves a reaction with a known amount of iodine, which is generated by the oxidation of potassium iodide with potassium iodate. The iodine reacts with the thiosulfate ions in a 1:2 mole ratio, resulting in the formation of tetrathionate and iodide ions. The endpoint of the titration is reached when all the iodine has been consumed, which is indicated by a color change from yellow (due to iodi
ne) to colorless.
    ### Reagents and Apparatus.
    Reagents:
    Sodium thiosulfate solution (approximate concentration of 0.1 M)。
    Potassium iodide (KI)。
    Potassium iodate (KIO3)。
    Starch solution (1%)。
    Sulfuric acid (H2SO4)。
    Apparatus:
    Burette (25 mL)。
    Erlenmeyer flask (250 mL)。
    Analytical balance.
react with    Pipettes (10 mL and 25 mL)。
    Indicator.
    ### Procedure.
    1. Prepare the iodine solution: Weigh approximately 0.3 g of potassium iodate and dissolve it in 100 mL of water. Add 10 mL of 1% starch solution and 10 mL of 1 M sulfuric acid to the solution.
    2. Standardize the sodium thiosulfate solution: Pipette 25.00 mL of the iodine solution into an Erlenmeyer flask. Add 10 mL of 1 M sulfuric acid and titrate with the sodium thiosulfate solution from a burette until the yellow color of iodine disappears. Record the volume of thiosulfate solution used.
    3. Repeat the titration: Perform at least two additional titrations to ensure accuracy. Calculate the average volume of thiosulfate solution used.
    ### Calculations.
    The molarity of the sodium thiosulfate solution can be calculated using the following formula:
    Molarity (Na2S2O3) = (Molarity of KIO3  Volume of KIO3  2) / Volume of Na2S2O3。
    where:
    Molarity of Na2S2O3 is the molarity of the sodium thiosulfate solution to be standardized.
    Molarity of KIO3 is the known molarity of the potassium iodate solution used (typically 0.01 M)。
    Volume of KIO3 is the volume of potassium iodate solution used (25.00 mL)。
    2 is the mole ratio between thiosulfate and iodate (2 moles of thiosulfate react with 1 mole of iodate)。
    Volume of Na2S2O3 is the average volume of sodium thiosulfate solution used in the titration.

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