24.9 The Combustion of Acetylene

Chemical Concept Demonstrated: chemistry of alkynes


Crushed ice is covered over the bottom of a beaker.

Calcium carbide (CaC2) is sprinkled over the ice.

A match is dropped into the beaker.


    An exothermic reaction occurs.

Explanation (including important chemical equations):

    Calcium carbide reacts with water to form acetylene.

        CaC2 (s) + H2O (l) --> Ca2+ (aq) +2 OH- (aq) + H2C2 (g)

    In the presence of a flame, acetylene reacts with oxygen to form carbon dioxide and water.

         2 H2C2 (g) + 5 O2 (g) --> 4 CO2 (g) + 2 H2O (g)

    Because of the visual display, this demonstration is sometimes referred to as "fire rocks" (see demonstration 5.20k).

    Additional calcium carbide/acetylene chemistry can be seen in the carbide cannon demonstration (see demonstration 5.20j).