1. Clock Reaction (Initial rate method)

1.6. Iodine Clock Reaction: Hydrogen Peroxide and Iodide Ion with Fixed Sodium Thiosulfate

Chemical equation
o \( \text{H}_2\text{O}_2 + 2 \text{I}^- + 2 \text{H}^+ \rightarrow \text{I}_2 + 2 \text{H}_2\text{O} \)
o \(\text{I}_2 + 2 \text{S}_2\text{O}_3^{2-} \rightarrow 2 \text{I}^- + \text{S}_4\text{O}_6^{2-} \)
o Indicator: Starch

Color change
o Initial solution
- Iodine (I2\text{I}_2) is produced and immediately reacts with thiosulfate ions \(\text{S}_2\text{O}_3^{2-}\)
- Colorless

o Final solution
- Thiosulfate ions are entirely consumed and free iodine accumulates in solution
- Dark blue