Experiment: Preparation of 100 mL of Aqueous Iodine Solution (Lugol’s Iodine Solution)

Preparation of 100 mL of Aqueous Iodine Solution (Lugol’s Iodine Solution)


Aim:
To prepare 100 mL of aqueous iodine solution using iodine and potassium iodide in purified water.

Reference:-

Requirements (Apparatus and Chemicals):

Chemicals

  • Iodine – 5 g
  • Potassium iodide – 10 g
  • Purified water – up to 100 mL

 

Apparatus

  • Beaker (100 mL)
  • Glass rod
  • Measuring cylinder
  • Funnel
  • Volumetric flask (100 mL)
  • Filter paper

Theory:
Iodine alone is sparingly soluble in water, but its solubility increases in the presence of potassium iodide due to the formation of a soluble triiodide complex (I₃⁻). The reaction involved is:
I₂ + I⁻ → I₃⁻
This results in a clear brown-colored aqueous iodine solution known as Lugol’s iodine, which is used as an antiseptic and as a reagent in chemical analysis.

Procedure:

  1. Weigh 10 g of potassium iodide and transfer it into a clean beaker.
  2. Add about 30–40 mL of purified water and stir until the potassium iodide completely dissolves.
  3. Add 5 g of iodine crystals to the KI solution and continue stirring until the iodine fully dissolves, forming a clear brown solution.
  4. Transfer the solution into a 100 mL volumetric flask using a funnel.
  5. Rinse the beaker with a small quantity of purified water and add the rinsing to the flask to ensure complete transfer.
  6. Make up the volume to 100 mL with purified water.
  7. Mix the solution thoroughly.
  8. Filter if necessary to remove any undissolved iodine particles.
  9. Store the solution in a tightly closed amber-colored bottle, protected from light.

Observation:
A clear, brown-colored solution is obtained.

Result:
100 mL of aqueous iodine solution (Lugol’s solution) was successfully prepared.

(On Blank Side)

Formula Table:

Ingredient

Quantity

Purpose

Iodine (I₂)

5 g

Active antiseptic agent

Potassium Iodide (KI)

10 g

Solubilizing agent for iodine

Purified Water

q.s. to 100 mL

Solvent and vehicle

 

Label:
Aqueous Iodine Solution (Lugol’s Solution)
Each 100 mL contains:

  • Iodine – 5 g
  • Potassium Iodide – 10 g
  • Purified Water – q.s. to 100 mL
    Store in a well-closed, light-resistant container.