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2.4 MB, 36 seconds File: MOVIES/CCACL/CLACET.MOV

Voiceover
Chips of calcium carbide are placed on a watch glass inside a cylinder of chlorine. Water is slowly dripped onto the calcium carbide generating acetylene gas. The acetylene reacts rapidly with the chlorine producing clouds of carbon. When a stopper from a bottle of aqueous ammonia is brought near the flame, white fumes of ammonium chloride are produced indicating the presence of hydrogen chloride. Although acetylene continues to be generated, the reaction with chlorine ceases when all of the chlorine has been consumed.

Discussion
Acetylene (ethyne) gas is generated by reacting calcium carbide with water. The reaction is carried out in an atmosphere of chlorine gas in a glass cylinder. The acetylene reacts vigorously with the chlorine, producing a yellow flame and black soot. The products of the reaction include carbon and hydrogen chloride. The presence of hydrogen chloride is demonstrated by bringing the stopper from a bottle of aqueous ammonia above the glass cylinder. A smoke of ammonium chloride forms. The quantity of calcium carbide is large enough so that chlorine is the limiting reactant, and eventually it can be seen that calcium carbide continues to react with water to generate acetylene, but the flame and soot disappear.

Acetylene (ethyne) gas is commonly generated by reacting calcium carbide with water. The equation is

CaC₂(s ) + 2 H₂O(l ) --> Ca(OH)₂(aq ) + C₂H₂(g )

Acetylene gas and chlorine react upon contact at room temperature, so when acetylene is generated in a chlorine atmosphere it immediately inflames. The equation for the principal reaction is

C₂H₂(g ) + Cl₂(g ) --> 2 HCl(g ) + 2 C(s )

The solid carbon (soot) produced imparts a bright yellow color to the flame when heated to a high temperature. When it cools it forms black smoke.