📖 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

Reaction Mixture
Ready to mix
Select variables and start

⏱️ Timer

0.0
seconds
Reaction Time
--
Previous runs:

Predict Before You Mix

Standard conditions (0.02 M KIO₃, 25 °C, 10 mL NaHSO₃) give a delay of about 10 s. Set your variables above, then predict how your delay will compare — and why. The timer stays locked until you commit a prediction.

Tip: higher concentration and higher temperature speed the rate (shorter delay); more NaHSO₃ means more bisulfite to consume first (longer delay).

Set your variables, then lock your prediction to unlock the timer.

📚 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!

Lab Journal — Observation vs Interpretation

Start the reaction to see observations...

⚠️ Safety — Iodine Clock Reaction