Department of Chemistry and Biochemistry

Iodine Clock Reaction

Solutions

• Solution A: 2gm KIO3 in 1 liter H2O
• Solution B: Dissolve 2gm soluble starch in 500ml boiling water,

                   add 0.4gm NaHSO₃ + 5ml 1.0M H₂SO₄,
                   then bring up to 1 liter.

Procedure

1. Mix equal volumes A + B with stirring.
2. Varying volumes gives different times.

1) 160ml A
2) 160ml B

3) 80ml A + 160 ml H₂0
4) 80ml B

5) 40ml A + 240ml H₂0
6) 40ml B

3. Mixing 1 + 2, 3 + 4, and 5 + 6, gives relative times of 1, 0.5, 0.25.

Reactions

IO₃^- + 3HSO₃^- --> I^- + 3SO₄^2- + 3H⁺

6H⁺ + IO₃^- + 5I^- --> 3I₂ + 3H₂O

I₂ + starch --> (blue)

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Last Updated: 5/23/02