Underwater Flashes

Alternate titles:

Underwater Fireworks

To show the dramatic exothermic reaction between chlorine and acetylene gases.

Hydrochloric acid is acutely corrosive and toxic. Avoid skin contact and inhalation of fumes.
Calcium carbide releases flammable gases in contact with water, is corrosive, and is a severe eye/skin irritant with acute organ toxicity. Avoid contact and keep away from water.
Chlorine gas is extremely poisonous, and care should be taken not to produce more than will react away.
Potassium permanganate is an oxidizer, which presents a significant hazard for extreme exothermicity. It is also corrosive, an acute systemic toxin, and and aqueous environmental hazard.
Wear approved safety goggles and gloves.

Bend the glass tubing and insert it into the rubber stopper, along with the pipet.
1. Assemble as shown:
Place the KMnO₄ in the test tube. Fill the Beral pipette with concentrated HCl and place the assembly in the test tube, being careful not to squeeze the pipet bulb.
Fill the hydrometer with water.

To begin generating chlorine gas, squeeze several drops of HCl from the pipet onto the KMnO₄. The chlorine gas will be delivered into the hydrometer and bubbles should appear. Be careful to generate only enough chlorine to produce the reaction.
Add 2 or 3 pieces of calcium carbide to the hydrometer and observe the flashes which are produced when the chlorine and acetylene react. Additional HCl may be added to generate enough chlorine gas to continue the reaction.

The sparks result from the exothermic addition of chlorine across the triple bond. Some evidence suggests that the product is actually a chlorinated polymer of acetylene.

The aqueous products of this reaction are extremely dilute and can be poured down the sink.

This demo adapted from the demo library of the Chemistry department at the University of Illinois at Urbana-Champaign.
ICE Chemistry Fundamentals Workshop, Mt. San Antonio College, 1993.