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Lesson 15:

Combustion Reactions

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Concepts conveyed | Materials | Procedure | Benefits | Resource

Concepts conveyed:

The purpose of this classroom activity is to demonstrate the combustion reaction of sugar in air and to illustrate the importance of a catalyst.

Materials:

  • 2 sugar cubes
  • cigarette ashes (from one cigarette)
  • tongs
  • candle
  • matches

Procedure:

Discuss the general formula for a combustion reaction and explain the purpose of a catalyst.

The general reaction for the complete combustion of sugar is:

C6H12O6 + 6 O2 —> 6 CO2 + 6 H2O

A catalyst is a chemical substance that participates in a chemical reaction and influences its speed without undergoing permanent change.

Using tongs, hold one sugar cube in the edge of the flame from the candle. It will not burn, only melt in the hot flame. Rub the second cube in the cigarette ashes thoroughly, and then hold it in the edge of the flame. It will continue to burn some time after removal from the flame. The ashes are a catalyst to the combustion of the sugar. The ashes are not a direct part of the reaction, but must be present in order for the reaction to progress.

Benefits:

  • This activity can be used to allow students to actively participate in the lesson. The instructor can ask for volunteers to help with the activity.

Resource:

  • Schwartz, A. T., Bunce, D. M., Silberman, R. G., Stanitski, C. L., Stratton, W. J., & Zipp, A. P. Chemistry in Context; American Chemical Society: Washington, DC, 1994; p 401.
  • Chemistry for Museums: A Manual of Chemistry Demonstrations; Center of Science and Industry: Columbus, OH, 1976; Show #7, Demonstration #10; Project Funded by a National Science Foundation Grant #7423549.