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Refering to the image attached (Winkler method), what is the function of sodium thiosulphate and why do we need to add in the solution until it turns into pale yellow colour?

Refering to the image attached (Winkler method), what is the function of sodium thiosulphate and why do we need to add in the solution until it turns into pale yellow colour?

Chemistry
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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Refering to the image attached (Winkler method), what is the function of sodium thiosulphate and why do we need to add in the solution until it turns into pale yellow colour?
Dissolved Oxygen 5. If oxygen is present, a brownish-orange cloud of precipitate will develop. Allow the precipitate to settle for 30 minutes. 6. Add 1 mL of concentrated sulphuric acid (Winkler 3) using pipette. Again, hold the pipette just above the surface of the sample. 7. Re-stopper the bottle, shake and invert several times until the precipitate dissolves completely. After adding Winkler 3, the solution is stable. Therefore, it can be stored in a dark, cool place for up to 8 hours if titration analysis cannot be carried out immediately. Add 1 ml Wrinkler 3 Invert the bottles to mix If oxygen is present. a brownish-orange cloud of precipitate will develop. Allow the precipitate to settle for 30 minutes. 8. Transfer 50 mL of sample into an Erlenmeyer flask and titrate with sodium thiosulphate (0.025 N) until the solution turn to a pale yellow colour. Transfer 50 ml sample 9. Add 1 mL of starch indicator and a blue colour will develop. 10. Continue titration until the sample turn colourless. 11. Record the exact volume of sodium thiosulphate used to titrate the sample.
Transcribed Image Text:Dissolved Oxygen 5. If oxygen is present, a brownish-orange cloud of precipitate will develop. Allow the precipitate to settle for 30 minutes. 6. Add 1 mL of concentrated sulphuric acid (Winkler 3) using pipette. Again, hold the pipette just above the surface of the sample. 7. Re-stopper the bottle, shake and invert several times until the precipitate dissolves completely. After adding Winkler 3, the solution is stable. Therefore, it can be stored in a dark, cool place for up to 8 hours if titration analysis cannot be carried out immediately. Add 1 ml Wrinkler 3 Invert the bottles to mix If oxygen is present. a brownish-orange cloud of precipitate will develop. Allow the precipitate to settle for 30 minutes. 8. Transfer 50 mL of sample into an Erlenmeyer flask and titrate with sodium thiosulphate (0.025 N) until the solution turn to a pale yellow colour. Transfer 50 ml sample 9. Add 1 mL of starch indicator and a blue colour will develop. 10. Continue titration until the sample turn colourless. 11. Record the exact volume of sodium thiosulphate used to titrate the sample.
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