Hydrogen Peroxide Decomposition by Iodide
Publication information:
Abstract
30% Hydrogen peroxide in a large round bottom flask decomposes rapidly to hissing steam and oxygen when potassium iodide is added.
[https://harvard.hosted.panopto.com/Panopto/Pages/Viewer.aspx?id=c3f365a2-b78a-437a-8a5f-ae37015c4ef0 video of decomposition of hydrogen peroxide by iodide]
What it Shows
When the H2O2 solution is at room temperature, no reaction appears to be happening. But the reaction is just very, very slow. The dramatic effect of a catalyst on the decomposition rate of H2O2 is immediately evident when potassium iodide is added. The color changes also indicate that the KI returns to its original state after the reaction and is not consumed.
Setting it Up
Safety:
Wear safety goggles and gloves. Keep the audience at a good distance away. Make sure the flask is stable and the mouth is pointed directly up. Make sure there is nothing directly above the opening of the flask. 30% H2O2 is a reactive hazard, and will burn and bleach skin. After the reaction, the flask and solution is hot, contains potassium iodide and water only and is not a hazard.
Demonstrating it:
The 12L Round Bottom Flask is set on white C-Fold towels covering a large cork ring on the lab bench. 100-150 mL of 30% hydrogen peroxide is carefully poured in. The liquid should be visible against the white towels from the perspective of the class, and any camera, if used. The catalyst is 5 g of potassium iodide in a small plastic weighing boat labeled KI.
Put on safety gear. Add the KI in one smooth motion and get back!
When the KI hits the hydrogen peroxide, it changes color to brown as the active catalytic form of the iodide is formed. This shows up well against the white towels. The brown region bubbles and spreads, and rapidly the entire volume of hydrogen peroxide releases oxygen, and then boils up to nearly filling the flask. Hot oxygen and steam shoot out of the mouth of the flask, to the ceiling if you're lucky.
If the instructor wishes, another aliquot of 75 - 100 ml of hydrogen peroxide can be added, to show that the catalyst is still present. The solution turns brown and bubbles, but does not react as vigorously as the first time.
Cleanup and Disposal:
Once the solution is cool to touch, carefully pour it down the drain with lots of water.
Since we use the same 12 L flask, it must be rinsed of all trace of iodide before putting it upside down to drip dry. Store on the large cork ring on the shelf with the neck low to keep dust from settling. A lot of things act as a catalyst for decomposing hydrogen peroxide, so keep that flask clean!
Comments
The decomposition reaction taking place is 2H2O2 (aq) --> 2H2O (l) + O2 (g) + heat. The reaction is highly exothermic. The KI acts as a catalyst to speed up the reaction rate with the following mechanism:
H2O2 (aq) + I- (aq) -> OI- (aq) + H2O (l)
H2O2 (aq) + OI- (aq) -> H2O (l) + O2 (g) + I- (aq)
There are other notable variations to this hydrogen peroxide decomposition reaction, as well as many different substances that will catalyze the decomposition including potatoes, liver, manganese dioxide, and yeast. Sodium iodide can be substituted for the potassium iodide.
1) Elephant's toothpaste. Always a crowd-pleaser! Click here to watch a video!
2) Genie in the bottle. Mystify your students by rubbing a magic lamp from which steam emerges! Read about it here.
3) Biological catalysts - Enzymes: Catalase in potatoes and liver will speed the decomposition of hydrogen peroxide. Here is a brief description describing these enzyme catalysts.
References and Acknowledgements:
Developed by Daniel Rosenberg, circa ___.
Johnson, Ken (1967) "Chemical Kinetics of KI Catalyzed H2O2 Decomposition," Iowa Science Teachers Journal: Vol. 5: No. 2, Article 12.
Steve Spangler. (2013, August 22). Back to school science elephant’s toothpaste - cool science experiment. YouTube. https://youtu.be/ZbUOPAgJIOQ?feature=shared
Spangler, Steve. (2023, August 17). Genie in a Bottle. https://stevespangler.com/experiments/genie-in-a-bottle/
University of York, Department of Chemistry. (1995, September). Decomposing Hydrogen Peroxide. https://www.york.ac.uk/chemistry/about/schools/chemrev/projects/peroxide/
Full text
30% Hydrogen peroxide in a large round bottom flask decomposes rapidly to hissing steam and oxygen when potassium iodide is added.
[https://harvard.hosted.panopto.com/Panopto/Pages/Viewer.aspx?id=c3f365a…; video of decomposition of hydrogen peroxide by iodide]
What it Shows
When the H2O2 solution is at room temperature, no reaction appears to be happening. But the reaction is just very, very slow. The dramatic effect of a catalyst on the decomposition rate of H2O2 is immediately evident when potassium iodide is added. The color changes also indicate that the KI returns to its original state after the reaction and is not consumed.
Setting it Up
Safety:
Wear safety goggles and gloves. Keep the audience at a good distance away. Make sure the flask is stable and the mouth is pointed directly up. Make sure there is nothing directly above the opening of the flask. 30% H2O2 is a reactive hazard, and will burn and bleach skin. After the reaction, the flask and solution is hot, contains potassium iodide and water only and is not a hazard.
Demonstrating it:
The 12L Round Bottom Flask is set on white C-Fold towels covering a large cork ring on the lab bench. 100-150 mL of 30% hydrogen peroxide is carefully poured in. The liquid should be visible against the white towels from the perspective of the class, and any camera, if used. The catalyst is 5 g of potassium iodide in a small plastic weighing boat labeled KI.
Put on safety gear. Add the KI in one smooth motion and get back!
When the KI hits the hydrogen peroxide, it changes color to brown as the active catalytic form of the iodide is formed. This shows up well against the white towels. The brown region bubbles and spreads, and rapidly the entire volume of hydrogen peroxide releases oxygen, and then boils up to nearly filling the flask. Hot oxygen and steam shoot out of the mouth of the flask, to the ceiling if you're lucky.
If the instructor wishes, another aliquot of 75 - 100 ml of hydrogen peroxide can be added, to show that the catalyst is still present. The solution turns brown and bubbles, but does not react as vigorously as the first time.
Cleanup and Disposal:
Once the solution is cool to touch, carefully pour it down the drain with lots of water.
Since we use the same 12 L flask, it must be rinsed of all trace of iodide before putting it upside down to drip dry. Store on the large cork ring on the shelf with the neck low to keep dust from settling. A lot of things act as a catalyst for decomposing hydrogen peroxide, so keep that flask clean!
Comments
The decomposition reaction taking place is 2H2O2 (aq) --> 2H2O (l) + O2 (g) + heat. The reaction is highly exothermic. The KI acts as a catalyst to speed up the reaction rate with the following mechanism:
H2O2 (aq) + I- (aq) -> OI- (aq) + H2O (l)
H2O2 (aq) + OI- (aq) -> H2O (l) + O2 (g) + I- (aq)
There are other notable variations to this hydrogen peroxide decomposition reaction, as well as many different substances that will catalyze the decomposition including potatoes, liver, manganese dioxide, and yeast. Sodium iodide can be substituted for the potassium iodide.
1) Elephant's toothpaste. Always a crowd-pleaser! Click here to watch a video!
2) Genie in the bottle. Mystify your students by rubbing a magic lamp from which steam emerges! Read about it here.
3) Biological catalysts - Enzymes: Catalase in potatoes and liver will speed the decomposition of hydrogen peroxide. Here is a brief description describing these enzyme catalysts.
References and Acknowledgements:
Developed by Daniel Rosenberg, circa ___.
Johnson, Ken (1967) "Chemical Kinetics of KI Catalyzed H2O2 Decomposition," Iowa Science Teachers Journal: Vol. 5: No. 2, Article 12.
Steve Spangler. (2013, August 22). Back to school science elephant’s toothpaste - cool science experiment. YouTube. https://youtu.be/ZbUOPAgJIOQ?feature=shared
Spangler, Steve. (2023, August 17). Genie in a Bottle. https://stevespangler.com/experiments/genie-in-a-bottle/
University of York, Department of Chemistry. (1995, September). Decomposing Hydrogen Peroxide. https://www.york.ac.uk/chemistry/about/schools/chemrev/projects/peroxid…