Iodine Clock Reaction
- Page ID
- 131403
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Required Training |
Required PPE |
|---|---|
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UC Lab Safety Fundamentals |
Lab coat, safety glasses/goggles, nitrile gloves |
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Equipment |
Chemicals |
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230 mL Deionized Water |
20 mL 0.25 M NaHSO3, MW = 104 (2.6 g/100 mL) Sodium Bisulfite |
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400 mL Beaker |
100 mL 0.1 M KIO3, MW = 214 (2.14 g/100 mL) Potassium Iodate |
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600 mL Beaker |
5 mL 1% Starch Solution (no more than 3 months old) |
Procedure:
- In a 400 mL beaker, add 100 mL 0.1M KIO3, 5 mL 1% starch, and 100 mL H2O
- In a 600 mL beaker, put in 20 mL 0.25M NaHSO3, and 130 mL H2O
- Mix the two solutions and after a short delay, the clear solution will instantly turn a dark blue/black (~10 seconds)
Discussion:
Bisulfite anions (HSO3-) from NaHSO3 reduce KIO3 to form iodide anions (I-), which further react with KIO3 to form iodine (I2). In solution I2 reacts with I to form triiodide anions (I3-). I3- is immediately reduced back to I- by any remaining HSO3-. Once the supply of HSO3- is exhausted, I3- persists in solution and reacts with starch molecules to form a dark blue starch-iodine complex. Excess I3- is a brown color in solution, and together this produces the dark blue/black color. As the concentration of I3- rises extremely quickly, the color change is almost instantaneous. The volume of NaHSO3 solution added to the reaction will change the time required for the color change – larger volumes will increase the delay, and smaller volumes will decrease it.
Hazards:
KIO3 is an oxidizer and should be kept away from flammable materials and reducing agents. NaHSO3 is a strong reducer and should be kept away from acids and oxidizing agents.
SOP
Strong Oxidizing Agent – Potassium Iodate
Strong Reducing Agent – Sodium bisulfite
Disposal (by Storeroom)
While stirring, slowly add solid sodium thiosulfate (Na2S2O3•5H2O) until the mixture is no longer blue. Flush this mixture down the drain with large quantities of water.