1.      Background Lesson 1 on the composition and layers of the atmosphere in this unit and on the MEECS Air Quality CD should be reviewed for possible use with groups that have not been introduced to these topics.

2.      Decide what type of model you will use to illustrate the reactants and products of a burning candle (kit, toothpicks and gum drops, or paper models). If the paper models are used to create molecules, prepare a set for each group of students using the Models of Atoms student resource. The set has one carbon atom, four oxygen atoms, and four hydrogen atoms that need to be cut out. Each notch represents a bond. The atoms fit together by linking the notches. Double bonds will be created in the oxygen and carbon dioxide molecules. Prepare transparencies of the Models of Molecules. Prepare a transparency of Models of Atoms and cut out the individual atoms.

3.      Prepare a saturated solution of calcium hydroxide (limewater) several days before needed to allow it to reach saturation. Place 100 mL of distilled water in a 250-mL bottle. Add 1.0 g Ca(OH)₂. Seal tightly to prevent access to atmospheric CO₂. Shake the solution and let it settle. If needed, filter the solution, let it settle, and use only the clear liquid. When CO₂ gas is bubbled through colorless limewater, Ca(OH)₂(aq), the limewater turns milky due to the formation of a calcium carbonate (CaCO₃(s)) precipitate. The chemical equation is:  CO₂ + Ca(OH)₂   g CaCO₃ + H₂O