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?)