Catalytic decomposition of Hydrogen Peroxide
Exothermic Reaction
Introduction:
The chemical formula for hydrogen peroxide is H2O2. It looks pretty similar to the chemical formula for
water, which is H20, except that hydrogen peroxide has an extra "O", an extra oxygen. Hydrogen
peroxide is not a very stable compound, so, it is always decomposing to water and oxygen, but under
normal conditions, the decomposition goes very slowly. In this reaction, tissues (liver and raddish)
containing the enzyme catalase is added to the reaction mixture making the reaction go much more
quickly.
2 H2O2 (aq) ---> 2 H2O (l) + O2 (g) +196.1 kJ/mol
We can predict the rate of reaction by observing two things: the rate of oxygen production and rate of
heat released.
Procedure with chicken liver:
1.
2.
3.
4.
5.
6.
Take a ziplock bag (a sandwich bag) and add about 20 ml of 3% hydrogen peroxide.
Using a thermometer or easy temp. probe measure and record the temperature of the mixture
Record the rate of oxygen formation (number of bubble per minute).
Add a small piece of chicken liver to the hydrogen peroxide and immediately close the bag.
Let the reaction run for few minutes.
Note the temperature and the rate of oxygen formation.
Caution!!! Let the gas out of the bag if it is overinflated
Procedure with radish:
7. Cut and grate the one piece of radish. Add 30 – 40ml of water (enough to cover the grated
radish) and using a hand held blend the grates radish to make a apple cause. Use a cheese cloth
to filter the debris. Use the filtrate as catalase enzyme.
8. Repeat steps 1-3.
9. Add about 10 ml of radish catalase enzyme to the hydrogen peroxide and immediately close the
bag.
10. Let the reaction run for few minutes.
11. Note the temperature and the rate of oxygen formation.
Caution!!! Let the gas out of the bag if it is overinflated
Data table:
Material
Initial
temp. (0C)
Final temp.
(0C)
Difference
in temp
Ini#
bubbles/min
Final
bubbles/min
Conclusions
Liver
Radish
Assessment:
1.
2.
3.
4.
5.
What is the role of liver and radish in this reaction?
What are the products of this reaction?
Is this reaction exothermic or endothermic? Explain
What evidence do you have that this was a chemical change and not a physical change?
Can you find a way to identify the gas produced in this reaction?