Demonstration of Evaporation and Condensation

(Can also be used for teaching about the water cycle, purification of liquids, etc.)

 

Preparation:

Set up an apparatus as shown. (Your next middle or high school should have the materials if you can't find them in your elementary school.)

 

Instead of the bent glass tubing, you can also use plastic tubing. But you need a short piece of glass through the rubber stopper onto which to slide the tubing.

Watch your hands when you push glass tubing into the rubber stopper. Add a tiny amount of vaseline or glycerine to make the tubing slip into the rubber stopper--and come out more easily.

Demonstration:

  1. Add some salt water (kids can taste this; sugar can also be used).
  2. Place stopper and complete set up.
  3. Place flask on a heading pad and bring to a boil.
  4. After some time, you will observe evaporation and steam in the tubing.
  5. Begin with small amount of liquid which will let you boil all the liquid away and leave you with a white solid substance.
  6. Better still: Use food coloring. The liquid in the goblet will be clear.

Productive Questions:

  1. What will happen if we heat the salt (sugar) water in the flask?
  2. Use EXPLAIN, ELABORATE, JUSTIFY questions to get as many students answer as deeply as they possibly can.
  3. Also use "Why do YOU think so. . .?" stems so that students seek to give their personal answers to your questions. You encourage reasoning rather than right-answerism.
  4. (When water boils:) What do you observe? How do you know?
  5. (About liquid in the goblet:) What do you think this liquid consists of? How can we find out? (tasting is one option, though another distilation should show that there won't be a residue.