Lab F report

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University of British Columbia *

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Chemistry

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Jan 9, 2024

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Lab F: Standardization of a Sodium Thiosulfate Solution Jayden Podmoroff 17122912 Partner: Josh Thomson Lab performed: Nov 2, 2018 Chem 121 L08 TA: Nitin Lab Submitted: Nov 16, 2018 1
Introduction: The purpose of this experiment was to find the standardize a provided sodium thiosulphate solution through titration using a dilute primary standard solution of potassium iodate. The standardized solution obtained from this experiment can be used as a secondary standard solution in future experiments. A primary standard solution is defined by a solution having been prepared by direct measurements of the mass of solute and the volume of solution, whereas a secondary standard solution is defined by a solution whose concentration cannot be determined directly from weight of solute and volume of solution. 1 Primary standard solutions are generally used to standardize solutions, such as sodium thiosulphate, and secondary solutions are generally used in more specific analytical experiments. This experiment involves two separate chemical reactions leading up to and during titration. Before titrating, a known quantity of iodine is produced from chemical reaction (1), where a known amount of iodate reacts with excess iodide in acid solution. 1 The iodine is then titrated with the sodium thiosulphate while using a starch indicator to mark the end point (reaction (2)). The corresponding reactions are given below. 1 KIO 3 + 5KI + 3H 2 SO 4 3I 2 + 3K 2 SO 4 + 3H 2 O (1) 2Na 2 S 2 O 3 + I 2 2NaI + Na 2 S 4 O 6 (2) 2
Procedure: The procedure of Lab F given by the First Year Chemistry Lab Manual 2 was followed as described below. In order to make the concentrated KIO 3 primary standard solution, 1.0126 g of potassium iodate was weighed using an analytical balance and then transferred into a 150 mL beaker. The potassium iodate was dissolved in the beaker and then transferred into a 250 mL volumetric flask and then inverted about 15 times to ensure proper mixture. The dilute KIO 3 primary standard solution was made by first pipetting 25.00 mL of the concentrated KIO 3 solution from a separate dry beaker into a 250 mL volumetric flask. The flask was then filled with deionized water up to the mark in order to dilute the solution and then inverted about 15 times to ensure proper mixture. Roughly 100 mL of the provided sodium thiosulphate solution was obtained in a beaker and used to fill a burette. 25.00 mL of the dilute KIO 3 standard solution was pipetted into a 125 mL Erlenmeyer flask. 0.2 g of potassium iodate was obtained using a scoop and mixed with the solution in the flask. 20 drops of 1 M H 2 SO 4 were then added to the solution under the fume hood, forming a brownish-yellow iodine solution. The solution obtained from the previous step was slowly titrated with the provided sodium thiosulphate solution until the iodine solution was a much lighter yellow. 5 drops of starch 3
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