“Aladdin’s Lamp” Demonstration
Many reactions produce heat. In fact, when people think of chemical reactions, heat production is often expected. However, it is unexpected to see a six-foot cloud of steam come pouring out of a flask. The “Aladdin’s Lamp” demonstration is an example of the startling effect of heat produced by rapid decomposition of hydrogen peroxide. It’s an old demonstration, but it never loses its appeal or educational value. If you have never used this demonstration, I suggest you try it. It’s easy and almost foolproof. It’s a great demonstration, but it isn’t magic – it’s just good old reaction enthalpy.

Equipment and Materials: ¼ teaspoon potassium iodide, KI     (fine granular) One large boiling flask (at least 500 mL) One rubber stopper to fit boiling flask String, 50 cm One empty tea bag

CAUTION:
This activity requires the use of hazardous components and has the potential for hazardous reactions. Please review the Safety Precautions section and relevant Materials Safety Data Sheets before beginning this activity.

Procedure:

1. Transfer 50 mL of 30% H₂O₂ to a large boiling flask (Don’t use more – handle with care!)
2. Empty a tea bag and refill it with ¼ teaspoon of fine granular KI
3. Using the string, suspend the tea bag in the neck of the boiling flask
4. Use the stopper to hold the tea bag in place
5. When the stopper is removed, the tea bag falls into the hydrogen peroxide
6. Step back from the flask and give it room. Be sure the mouth of the flask is pointed up and in a safe direction. A six-foot cloud of steam will erupt from the flask

Discussion:
In this case, the net reaction is:
      2H₂O₂ -> 2H₂O + O₂ + heat
It is believed to be a two-step mechanism, involving the production of IO^- ions, which are consumed in the second step:
      H₂O₂ + I^- -> H₂O + IO^-
      H₂O₂ + IO^- -> H₂O + O₂ + I^-
First, the KI dissolves to supply the I^- ions so there is a delay before the steam appears. But, once the reaction begins, there’s plenty of heat available to boil the water and to speed the reaction.

A brief consideration of the enthalpies of formation of the participants:
      H₂O₂: -45.69 kcal/mol in solution
      H₂O: -65.32 kcal/mol
      O₂: zero
The use of Hess’ Law will show that the decomposition liberates about 19.6 kcal/mole.

Our 50 mL of 30% hydrogen peroxide contains about 0.5 moles of the substance, so we can make a rough estimate of the amount of steam produced. Ignoring the elevation of boiling point and the heat required to heat the flask, and taking the specific heat of pure H₂O₂ as 0.3 cal/g/^oC, 3.46 kcal are needed to heat the reagents to boiling.

The reaction generates 9.42 kcal, so 5.96 kcal are available to make steam at 100^oC. About 11g of steam would be produced, and this occupies about 17.5 liters at 100^oC.

Safety Precautions:
Hydrogen peroxide is an extremely potent oxidizing agent. Skin contact will result in “burns”. The skin readily absorbs hydrogen peroxide and its oxidizing effects cause local capillary embolism. Peroxide decomposition reactions are highly exothermic. Do not use chipped or cracked glassware, or vessels that will react poorly to heat. Do not handle the glassware until sufficiently cooled.

Disposal:
Since the hydrogen peroxide is consumed in the reaction, no special disposal is needed.

Reference:
This is one of the fascinating reactions described in the ASC’s Chemical Demonstrations, Vol. 2 (Summerlin, Borgford & Ealy).

To try this interesting reaction, we recommend reading Chemical Demonstrations and following the safety procedures given in the book.

More Teaching Tips from Quantum coming soon!