Ask students to read the lines from the Coleridge poem. Ask them if they’ve ever seen a movie or read a book where the character(s) were at sea and needed fresh water. What did the characters try to do to get freshwater?
(Some students may have read the novel or seen the movie Life of Pi, in which the protagonist captures fresh water from evaporated seawater using a floating “solar still.”)
The three particulate illustrations shows air that has lots of water vapor in it. When the concentration of water vapor in the air gets high enough (relative to the temperature—it has to be cold enough), the water molecules clump together into liquid droplets. This transition from gas to liquid is called condensation. As more water condenses, droplets join together into larger drops and can fall as rain.
The water cycle diagram shows the processes of evaporation and condensation at work on a massive scale, in the water cycle.
Ask students to discuss the role that temperature plays in this process.
- In general, colder temperatures with high water vapor concentration in the air promote condensation. Higher temperatures and lower water vapor concentration work against concentration.
This illustration of the laboratory equipment shows how we can replicate the distillation process seen in the water cycle.
Underscore for students that the cold water circulating in and out of the condenser is only there to transfer heat away from the steam. None of that cold water passes into the tube where the steam is. All of the water that drips into the collection flask is condensed steam from the original salt water.
Ask students to label the equipment with the corresponding natural phenomena.
- Bunsen burner—sun
- salt water—the ocean
- condenser—cloud formation
- dripping condensation—rain
- collected fresh water—rivers and lakes