Introduction

The reaction of hydrogen peroxide with potassium iodide is demonstrated in a tall cylinder.  Saturated potassium iodide is added to a mixture of soap, glycerin, water, and hydrogen peroxide.  Oxygen and water vapor are trapped in soap bubbles resulting in a long, soapy snake.

2H2O2(aq)  —KI Catalyst   >  2H2O(g) + O2(g)

A large amount of KI is used and I2 is seen to form, presumably because of the oxidation of I- by the produced O2.                                                  

Supplies

Short List

  •   Goggles and gloves
  •   250 mL beaker
  •   100 mL beaker
  •   2-3 L cylinder
  •   700mL distilled water
  •   200mL clear dish soap
  •   Large tray
  •   Paper towels
  •   Crystallizing dish

Chemicals

  •   Sat. KI
  •   125mL of fresh 30% H2O2
  •   100mL glycerin

Prior to Lecture  (prep time ~ 5 min.)

1.  Prepare soap solution by mixing 200mL clear dish soap, 100mL glycerin, and 700mL distilled water.

2.  Prepare saturated KI (potassium iodide) by dissolving 100g KI in 100mL water with heat and stirring.  Continue to add 5g KI at a time until solution no longer dissolves additional solid.

3. Before lecture, pour 100mL soap solution into large (2-3L) cylinder.  Pour 50mL saturated KI solution into labeled 100mL beaker.  Pour 125mL of fresh 30% H2O2 into labeled 250mL beaker.

4. Provide the following equipment:

            a. large tray to catch overflow

            b. goggles

            c. gloves

            d. paper towels

Notes:

1.  Label the soap solution in the cylinder solution (1);  the saturated KI solution, solution (2);  and the H2O2  solution (3) so that the demo presenter doesn’t have to remember which solution to pour in first.

2.  Use a large squat cylinder placed on an inverted large crystallizing dish in a large tray to catch the overflow.  Place whole apparatus over the lecture bench light.

Vomiting pumpkin:

1.      Carve the pumpkin and secure saran wrap inside to cover the eyes and nose.

2.      Place crystallizing dish inside pumpkin.

3.      Use the same amount of soap and KI solutions, but only 75 mL of H2O2solution.

4.      If presenting solutions 2 and 3 in cylinders, place cylinders inside beakers to prevent tipping.

5.      Place pumpkin on top of an inverted small white tray inside a large white tray with a beige “cafeteria” tray placed flush against the front of the large tray to catch any overflow from the pumpkin’s mouth.

To Conduct Demonstration:

1.      Pour 125mL of 30% hydrogen peroxide into a tall cylinder containing 100mL of soap solution.

2.      Carefully add 50mL saturated KI solution to the cylinder.  The reaction proceeds very quickly and shoots up and out of the             cylinder.

Safety and Disposal

Goggles should be worn.  Wear gloves when handling 30% hydrogen peroxide.  Reaction produces heat.