Under-Water Fireworks. Ethyne Flame in Chlorine

When bubbles collide bright flash occurs.

Scientific name: Chlorine and ethyne react vigorously.

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Fire and Flame 42 - Ethyne Flame in Chlorine

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Safety

This demonstration should be performed in the fume hood. Place a safety screen. Wear eye protection goggles and gloves.

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

Reaction formula

CaC2 + 2H2O → C2H2 + Ca(OH)2

CaC2 + H2SO4 → C2H2 + CaSO4

ClO- + Cl- + 2H+ → Cl2 + H2O

C2H2 + Cl2 → CHCl=CHCl

C2H2 + 2Cl2 → CHCl2–CHCl2

C2H2 + Cl2 → 2C + 2HCl

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. Since chlorine is a very hazardous gas this experiment should be performed only in a fume hood.
  2. Сalcium carbide is used to obtain ethyne. Chlorine gas is obtained by treating household bleach with 2M sulfuric acid.
  3. Pour the acid solution into the beaker.
  4. Add one pea-sized piece of calcium carbide. The reaction forming ethyne gas begins.
  5. Using a pipette add about 1 ml of household bleach into the beaker. The reaction of bleach and sulfuric acid gives chlorine gas.
  6. The bubbles of gases move toward the surface and when they met a small explosion takes place. The walls of the vessel turn black because of carbon formation.
  7. This experiment could be performed in a little bit more complicated but safer way. Prepare a stand with a clamp, flask, high glass cylinder, glass tube with u-end and flexible connection.
  8. Fill the cylinder with water.
  9. Pour some acid into the flask. Set the flask on the stand.
  10. Add some bleach into the flask. Close the flask with a stopper connected with a glass tube.
  11. Put the glass tube down the cylinder.
  12. Drop a few pieces of calcium carbide into the cylinder.
  13. The reaction with flashes begins.

Scientific background

One of the most common ways to obtain ethyne in the laboratory is the reaction of carbon carbide and water. This reaction was discovered by Friedrich Wokler in 1862 and was widely used for producing ethyne in carbide lams. Household bleach contains sodium chloride and sodium chlorate and in acidic medium gives chlorine. Both gases are very reactive. In an ethyne molecule three pairs of electrons are shared between two carbon atoms. Chlorine needs just one more electron to complete its outermost level. When the compounds meet they easily react. The electrophilic halogen attacks the triple bond of ethyne and adds to the hydrocarbon molecule across the triple bond. When the reaction proceeds readily with an explosion another mechanism is realized. Chlorine removes hydrogen from ethyne forming carbon and hydrochloride.

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Published on 08 October 2015

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