Bombardier Beetle Lab
The bombardier beetle (Coleptera: Carabidae) is a ground beetle found in North and
South America, Europe, Africa and Australia. This insect possesses a unique method of
defense: it sprays predators with hot corrosive liquid that is under pressure. Within its
abdomen the beetle has two chambers. One contains a mixture of hydrogen peroxide and
hydroquinone; the other contains a mixture of the enzymes catalase and peroxidase.
When threatened, the beetle mixes the contents of these two chambers. The enzymes
catalyze the decomposition of hydroquinone and hydrogen peroxide to water, p-quinone
and oxygen. The heat generated from the reaction brings the mixture to boiling, building
up pressure that results in the mixture being expelled explosively from the chamber. The
oxygen generated by the reaction acts as a propellant, causing the mixture to pop out of
the abdomen through the abdominal tip, which can be aimed by the beetle. A single
beetle can discharge up to 29 consecutive times and can spray at a distance of up to 4
times its body length.
Activities:
Before you begin the lab, you must figure out the relative amounts of each chemical that
you will need. First, write out and balance the overall equation:
+
Hydroquinone

hydrogen peroxide
+
quinone
+
oxygen
water
The beetle typically has solutions of 0.25 micromol hydroquinone and 7.4 micromol
hydrogen peroxide per milligram aqueous solution. Based on the results of balancing the
above equation, which compound is the limiting reagent in the beetle?
If we will be using 10 mg of hydroquinone, how much hydrogen peroxide will you need?
The molecular weight of hydroquinone is 110.1 g/mol. The molecular weight of
hydrogen peroxide is 34.01 g/mol.
Catalase is sold by Sigma and other chemical companies in quantities of units. One unit
is defined as the amount of catalase that will decompose 1 micromole of hydrogen
peroxide per minute at 25 Celsius. Our formulation contains 2,000 to 5,000 units per
milligram. Given the number of moles in our reaction, how much catalase will you need?
Peroxidase is sold in units that correspond to a chemical we aren’t using, so I’ve figured
out the amount you’ll need experimentally in the lab. Each of you will obtain an
ependorf tube containing the proper amount of peroxidase.
After you’ve had Ms. Camasta or Katy check your calculations, weigh out the correct
amounts of each chemical. In this experiment, we will allow hydroquinone to be the
limiting reagent, so round your amount of hydrogen peroxide up to the nearest milliliter.
Obtain two test tubes and a thermometer. Place the thermometer in the test tube. Add
the hydroquinone and hydrogen peroxide. Does anything happen? Why or why not? In
a separate test tube, combine the two enzymes. Switch your thermometer to this test
tube. Carefully, add the mixture of hydroquinone and hydrogen peroxide to the test tube
containing the enzymes and thermometer. Remember this is an explosive exothermic
reaction! Be careful! Also, one of the end products is irritating to skin, so don’t touch
the foam with your bare skin. Measure the change in temperature. Do you think this
would be an effective defense?