📖 Theory & Concepts ▼

Iodine Clock Reaction

A classic demonstration of chemical kinetics where the solution suddenly turns blue-black after a predictable delay.

Step 1: IO₃⁻ + 3HSO₃⁻ → I⁻ + 3SO₄²⁻
Step 2: IO₃⁻ + 5I⁻ + 6H⁺ → 3I₂ + 3H₂O
Final: I₂ + Starch → Blue-black complex

Factors Affecting Rate

  • Concentration: Higher [KIO₃] = faster reaction (shorter delay)
  • Temperature: +10°C roughly doubles the rate
  • Catalyst: Adding catalyst decreases activation energy
Rate Law:

Rate = k [IO₃⁻]ⁿ [HSO₃⁻]ᵐ

Determine order by varying concentrations and measuring delay time.

🎯 Objective

Study the rate of reaction between potassium iodate (KIO₃) and sodium bisulfite (NaHSO₃). Observe the sudden color change to dark blue when starch-iodine complex forms.

⚙️ Variables

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⏱️ Timer

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📚 How It Works

Step 1: Slow Reaction
IO₃⁻ + 3HSO₃⁻ → I⁻ + 3SO₄²⁻ + 3H⁺
Iodate slowly reduced to iodide
Step 2: Fast Reaction
IO₃⁻ + 5I⁻ + 6H⁺ → 3I₂ + 3H₂O
When HSO₃⁻ depleted, I₂ forms instantly
Step 3: Color Change
I₂ + Starch → Blue-Black Complex
Dramatic instant color change!

Observations

Start the reaction to see observations...