“Egyptian Night” experiment
How to make an eclipse in a beaker
To become the lord of darkness, all you need the vapors of clear solutions. In this experiment you’ll find out how to cause darkness in a beaker.
- Wear protective glasses and gloves.
- Avoid the hydrogen peroxide and skin from coming into contact with the skin and getting into the eyes and mouth.
Warning! Only under adults supervision.
Reagents and equipment:
- starch (10 g);
- 500 ml of a solution of sodium thiosulfate (10g) with potassium iodide (50g);
- concentrated hydrogen peroxide;
- 20% sulfuric acid solution;
Sprinkle starch into a beaker, add 200 ml of cold water and stir thoroughly. Then add 300 ml of hot water and stir again. Pour the solution of sodium thiosulfate with potassium iodide into the resulting solution. Then pour the mixture into beakers, adding diluted sulfuric acid and concentrated hydrogen peroxide. Observe the solutions turn dark in the beakers.
Several parallel reactions take place in the solution.
The first involves the oxidation of the iodide ions of hydrogen peroxide to molecular iodide:
H₂O₂ + 2I⁻ + 2H⁺ → I₂ + 2H₂O
The iodine that forms enters into a reaction with sodium thiosulfate until the sodium thiosulfate runs out.
2S₂O₃²⁻ + I₂ → S₄O₆2⁻ + 2I⁻
When the sodium thiosulfate has thoroughly reacted, iodine continues to form, entering into a reaction with starch and forming a blue iodine-starch complex.