Create a terrarium to enable fifth-graders to watch a microcosm of the water cycle in action. To build a terrarium, lay one or two inches of potting soil over a layer of fine gravel in a container that can be tightly sealed. Plant seeds in the soil, add water and seal the container. Observe the condensation that collects on the roof of the terrarium as the water cycles between gaseous and liquid forms.
A solar still is a low-tech water-purification system that collects condensation after using the heat of the sun to evaporate water. Place a jar in the middle of a large mixing bowl, then pour one or two cups of muddy or salty water into the bowl. Cover the bowl and jar with plastic wrap held in place with a rubber band, then place a small object in the center of the plastic to weigh it down over the jar. Place the bowl in the sun. Purified condensation will collect on the plastic and drip into the jar.
Students can explore the relationship between the temperature of an object and the condensation that forms on it to learn that more condensation will form on cold surfaces. Provide each student with four identical small glass beakers or metal bowls. Chill one in the freezer and one in the refrigerator, leave one at room temperature and warm one in direct sunlight or on a warm heating pad. Remove all four containers and wipe them with a cloth, then line them up and observe how much condensation gathers on each one.
Distillation is a process in which students can bring a liquid to the boiling point, capture the resulting vapor and expose it to reduced temperatures to condense it back into a liquid. Distillation can be used for purification, as in distilled water, or to concentrate an essence, as in distilled liquors. Set up a distillation by attaching a round-bottomed flask to a condenser using air-tight connections, then heating the liquid in the flask and run cold water through the condenser so that the vapor condenses and drips into a beaker.