Name  _________________________________________

Decomposition Reaction:

Also Known As Elephant Toothpaste

Purpose:  To observe a decomposition reaction.  A decomposition reaction occurs when one compound breaks down into two or more molecules or elements.

AB --------à A + B

We are also using a catalyst in this reaction to encourage the reaction to happen quickly.  The reaction will happen slowly but it’s more fun for this reaction if it happens quickly.  We are using Potassium iodide and/or Manganese dioxide as catalysts in this reaction.  They DO NOT bond to any of the reactants.  They exit the reaction exactly the same so we do not write them into the reaction equation.

Procedure:

1.     Put on goggles. 

2.     Get one test tube with a small amount of  Potassium iodide (KI).

3.     Obtain a graduated cylinder with  15 ml of concentrated Hydrogen peroxide and soap.

BE CAREFUL WITH HYDROGEN PEROXIDE!  IT CAN CAUSE BURNS AT THIS CONCENTRATION!

4.  All together we are going to drop the Hydrogen peroxide INTO the Potassium iodide.  Watch and record the results.

THIS REACTION IS HIGHLY EXOTHERMIC!!!  DO NOT TOUCH THE ELEPHANT TOOTHPASTE!  IT WILL TAKE UP TO 5 MINUTES TO COOL ENOUGH TO MOVE.

5.     Wait until Mrs. Jenner says you can clean up your lab.  The contents of the test tube will not hurt you (it’s mostly water with soap). The temperature is a safety concern.

6.     Clean up by bringing the test tube, test tube rack and tray up to the front of the class.  Give Mrs. Jenner the rack and test tube.  Take the tray to clean and dry.

7.     If everything is cleaned up in time, Mrs. Jenner will do a large elephant toothpaste for the class.

Conclusions:

1.     This is the equation for the decomposition of Hydrogen peroxide.  Potassium iodide (or Manganese dioxide) is a catalyst and it is not involved with the chemical reaction.  This is not balanced.  As a challenge, see if you can balance the equation.

H₂O₂    ------à        O₂    +      H₂O

  

2.     Describe what happened when Hydrogen peroxide decomposed into water and oxygen (what did the reaction look like).

3.     Why is the catalyst important in this reaction?

4.     Why is this a decomposition reaction?

5.     Why did we add soap?  (Hint:  The reaction makes oxygen gas.  Why is having soap fun when a gas is produced?)