Which Material Is Required to Make a Dilute Iodine Solution?

Preparing a dilute iodine solution, such as Lugol's iodine, is a common laboratory procedure used for starch detection, disinfection, and various analytical tests. The process involves dissolving elemental iodine in water with the aid of potassium iodide (KI), which increases iodine's solubility.

Materials Needed

• Elemental Iodine (I₂): The primary reagent, usually in crystalline form.
• Potassium Iodide (KI): Facilitates the dissolution of iodine in water by forming a triiodide complex.
• Distilled Water: Used as the solvent to ensure purity and prevent contamination.
• Glassware: Beakers, graduated cylinders, stirring rods.
• Brown Storage Bottle: To protect the solution from light and prolong shelf life.

Preparation Steps

1. Dissolve Potassium Iodide: Weigh the required amount of KI (e.g., 4 grams for 100 ml solution) and dissolve it in a portion of distilled water.
2. Add Iodine: Weigh the appropriate amount of elemental iodine (e.g., 1.3 grams for 100 ml solution) and add it to the KI solution. Stir until fully dissolved. The KI helps form a soluble triiodide ion (I₃⁻), allowing the iodine to dissolve in water.
3. Dilute: Add more distilled water to reach the desired final volume (e.g., 100 ml).
4. Storage: Transfer the solution to a brown or amber bottle, cap tightly, and store in a cool, dark place. Wrapping the bottle in aluminum foil can further protect it from light.

Practical Applications

• Starch Test: Used to detect the presence of starch in biological and chemical samples.
• Disinfectant: Iodine solutions are used as antiseptics in medical settings.
• Analytical Chemistry: Essential for titrations and redox reactions.

Key Takeaways

• Materials required: Elemental iodine, potassium iodide, distilled water, glassware, and brown storage bottle.
• Potassium iodide is essential for dissolving iodine in water.
• Proper storage extends the solution's shelf life and maintains its effectiveness.