Ultimate Cloud-Forming Apparatus

Introduction

An exquisitely simple demonstration that allows you to literally form a cloud with your own two hands. The thunder and lightning are up to you.

Concepts

• Condensation
• Cloud formation
• Gas laws

Materials

Safety Precautions

Although the materials provided in this kit are considered nonhazardous, always follow laboratory safety guidelines.

Disposal

The Cloud Forming Apparatus may be saved for future use.

Prelab Preparation

To assemble the stopper apparatus, place the tubing connector in the hole of the wide end of the stopper. Now place the rubber bulb on the opposite end of the tubing connector (see Figure 1).

Procedure

1. Add approximately 5 mL of water (room temperature) to the 500-mL boiling flask and place the stopper end of the stopper apparatus into the neck of the flask.
2. Shake the bottle to distribute the water on the interior surface and let it stand for a few minutes. This will allow time for some of the water to evaporate.
3. Remove the stopper assembly and tilt the flask sideways. Light a match and position it in the neck of the flask. Allow the match to burn for a few moments. Extinguish the match and collect some of the remaining smoke in the flask. Stopper the flask with the stopper assembly again.
4. Squeeze the bulb of the stopper assembly. The pressure in the bottle will increase significantly.
5. Quickly release the bulb and observe the bottle interior. A cloud will form. Repeat as often as desired.

Student Worksheet PDF

11839_Teacher1.pdf

Teacher Tips

• Consider introducing several different types of clouds. The attached PDF describes 10 types of clouds and at what altitude they typically form.
• Repeat the demonstration, only this time do not use the smoke from the match. No cloud will form. This will reinforce the concept that particles in the air are required for cloud formation.
• More precise examples and explanations of clouds can be found on the Skywatcher’s Cloud Chart (Flinn Catalog No. AP5301.)
• As an interesting aside, while going through a few squeeze and release cycles hold the bottle up to a fluorescent (overhead) light. By releasing and applying the pressure slowly, various colors may be evident (primarily purple and orange). One might suppose that light passing through the bottle is differentially scattered by the smoke particles as the pressure varies. Perhaps similar to the atmospheric effects seen at sunrise and sunset!

Discussion

This demonstration is somewhat analogous to cloud formation in the atmosphere. Squeezing the bulb dramatically increases the pressure (and ever slightly increases the temperature) inside the flask. At this higher pressure some of the water that was in the vapor phase returns to the liquid phase until a new equilibrium state is reached. When the pressure on the bulb is released, the pressure (and temperature) within the bottle drops suddenly, creating a partial vacuum. To reattain equilibrium, water now goes from the liquid phase to the vapor phase. At this point, the area above the liquid becomes saturated with water vapor which condenses on the “airborne” smoke particles (condensation nuclei) to form the cloud. This saturation is caused by unequal pressures of the vapor phases upon expansion of the bulb. The inequality of pressure can be thought of as an instantaneous partial vacuum.

References

Adapted from an item written by Bruce Parks that appeared in Connect, January/February, 1995. Connect is a publication of the Teachers Laboratory, Inc., Brattleboro, VT.

Feather, R. M.; Snyder, S. L.; Hesser, D. T. Merrill Earth Science; Glencoe: Illinois, 1993; p 258.