Underwater Fireworks

Beautiful sparks are observed when two gases react under water.

Scientific name: Chlorine gas is generated and reacts with acetylene.


"Underwater Fireworks" Reaction of Chlorine and Acetylene

by FlinnScientific

Подводный фейерверк, реакция ацетилена и хлора в воде. (химия)

by Thoisoi

Chlorine and acetylene-underwater firework

by chemistry858

"Underwater Fireworks" -- Acetylene & Chlorine Reaction

by ha1803

Chemistry experiment 50 - Underwater Explosions: Acetylene reacting with Chlorine

by koen2all

Underwater Fireworks demo

by MrGrodskiChemistry


Wear eye protection goggles and gloves. Since chlorine is very hazardous this experiment should be performed only in a fume hood or outdoors.

Always follow general safety recommendations. Please note that conducting chemistry experiments you must comply with the relevant legal procedures in your country.

Reaction formula

NaClO + 2HCl → Cl2 + H2O + NaCl

CaC2 + 2H2O → C2H2 + Ca(OH)2

C2H2 + Cl2 → C2H2Cl2

C2H2 + 2Cl2 → C2H2Cl4

Step-by-step instruction

WARNING! This experiment is dangerous! You should NOT perform this at home. ONLY carry out this experiment, if you are a trained chemist, and you understand local safety and legal requirements, which are required to perform such experiments

  1. For this experiment we need to obtain chlorine gas. Since it is very hazardous this experiment should be performed only in a fume hood.
  2. Prepare the following equipment: a graduated cylinder, gas delivery system, stand, and a 250 ml flask. The gas delivery system consists of a rubber stopper, short glass tube, flexible connection and J-shaped long glass tube. The length of the J-shaped long glass tube should exceed the height of cylinder.
  3. The required reagents are: household bleach (NaClO), concentrated hydrochloric acid (HCl), water (H2O) and calcium carbide (CaC2).
  4. Pour about 100 ml of household bleach into the flask.
  5. Set the flask on the stand.
  6. Fit the flask with a rubber stopper.
  7. Fill the cylinder with water.
  8. Put the J-shaped tube down into the cylinder.
  9. To generate chlorine add about 10 ml of concentrated hydrochloric acid to the flask with household bleach.
  10. Chlorine gas will be released from J-shaped tube.
  11. Add a few pieces of calcium carbide to the cylinder. When it comes in contact with water acetylene is formed.
  12. The reaction between two gases produce sparks.

Scientific background

In this experiment two gases reacts with bright flashes of light. The first gas is chlorine. It is generated when concentrated hydrochloric acid is added to household bleach:

NaClO + 2HCl → Cl2 + H2O + NaCl

The second one is acetylene. Acetylene is the product of the reaction between calcium carbide and water:

CaC2 + 2H2O --> C2H2 + Ca(OH)2

In the acetylene molecule two carbon atoms are bounded together with a triple bond. This means that three electron pairs are shared between to atoms. This bond is highly unsaturated. Chlorine atoms have high electron affinity and break down the triple bound of acetylene easily. They attach to the acetylene molecule forming dichloroethylene and tetrachloroethane. This reaction has low activation energy and occurs spontaneously when bubbles of the two gases collide.

C2H2 + Cl2 → C2H2Cl2

C2H2 + 2Cl2 → C2H2Cl4


Published on 14 March 2015

  • Fire
  • Heating with fire
  • Explosion
  • Poisoned gas
  • Organic
  • Electricity
  • Solution
  • Oxidation reduction
  • Color change
  • Precipitate
  • Gassing
  • Catalyst