Publication No. 12553
When potassium iodide is dropped into a flask containing 30% hydrogen peroxide, a “magical” genie appears in the form of water vapor and oxygen.
(for each demonstration)
Hydrogen peroxide, 30%, H2O2, 50 mL*
Potassium iodide, KI, 4 g*
Filter paper, qualitative, 9 cm*
Graduated cylinder, 50-mL or 100-mL
Volumetric flask, Pyrex®, 1000-mL
*Materials included in kit.
Hydrogen peroxide, 30%, will act as an oxidizing agent with practically any substance. It deserves the science teacher’s special handling and storage attention. This substance is severely corrosive to the skin, eyes and respiratory tract; a very strong oxidant; and a dangerous fire and explosion risk. Do not heat this substance. The reaction flask will get extremely hot; use only a Pyrex flask and hold with a towel around it to prevent burns. Do not point the mouth of the flask towards yourself or anyone else. Never tightly close a vessel containing hydrogen peroxide—it may explode. Wear chemical splash goggles, chemical-resistant gloves and chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Immediately clean up any liquid which may have spilled. Any liquid remaining in the flask may be flushed down the drain with excess water and disposed of by Flinn Suggested Disposal Method #26b. Remove any remains of the potassium iodide packet and dispose of in the regular trash according to Flinn Suggested Disposal Method #26a.
Student Worksheet PDF
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering PracticesAnalyzing and interpreting data
Disciplinary Core IdeasMS-PS1.A: Structure and Properties of Matter
MS-PS1.B: Chemical Reactions
HS-PS1.A: Structure and Properties of Matter
MS-PS1-2. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
Answers to Questions
The Magic Genie demonstrates the decomposition of hydrogen peroxide into oxygen gas and water vapor. The reaction is an exothermic reaction and will evolve a lot of heat. The reaction is:
The decomposition is catalyzed by iodide (I–) which is not changed during the reaction.
A catalyst is a substance that increases the rate of a reaction without being consumed during the reaction. The rate of decomposition of hydrogen peroxide is quite slow without the addition of a catalyst. There are two ways to tell if a substance is acting as a catalyst. First, it must speed up the reaction. Second, it is not consumed in the reaction. The same amount of the catalyst can be recovered as was originally added. If it were consumed, it would be a reactant and not a catalyst. In this demonstration, iodide was used as a catalyst.
There is an energy barrier that all reactants must surmount for a reaction to take place. This energy can range from almost zero to many hundreds of kJ/mol. This energy barrier is called the activation energy, Ea.
Reactants need to possess this amount of energy both to overcome the repulsive electron cloud forces between approaching molecules and to break the existing bonds in the reacting molecules. In general, the higher the activation energy, the slower the reaction.
The activation energy is related to the rate constant by the Arrhenius equation:
Where A is the frequency constant and is related to the frequency of collisions, R is the universal gas constant, and T is the temperature in K.
Catalysts are substances that speed up a reaction, but are not consumed in the reaction. Catalysts work by lowering the overall activation energy of the reaction, thus increasing the rate of the reaction.
In this reaction, I– acts as the catalyst and dramatically increases the rate of reaction.
Special thanks to Jim and Julie Ealy, The Peddie School, Hightstown, NJ, who provided us with the instructions for this activity.