Iodine-Thiosulfate titrations can be used to determine the concentration of sodium chlorate in bleach. We need to know how different concentrations will be used for different bleach. Chlorine reacts with sodium hydroxide to make sodium chlorate, NaCIO. A solution of about 12% NaCIO by mass is used in some water purifying to kiss bacteria. A solution of about 5% is used in household bleach products.
Iodine-Thiosulfate titrations involve redox reactions. They are used to find the concentration of a chemical that is a strong enough oxidising agent to oxidise iodine ions.
For bleach excess of iodine ions is added to the chlorate(I) ions which for this redox reaction:
CIO- + 2I- → I2 + Cl- + H2O
The iodine produce can be titrated using thiosulfate ions S2O32- in the following reaction:
2 S2O32- + I2 → S4O62- + 2 I-
At the end point of the titration can be clearly identified by adding starch solution. The end point is determined when the final trace of blue/black color is no longer visible.
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