National Chemistry Week - Experiments - Evaporation in Action

THE AIM:

To observe the process of evaporation.

WHAT YOU WILL NEED:

• 1 clear glass
• 1 rubber band

WHAT TO DO:

1. Fill the glass almost full with water.
2. Use the rubber band to mark the water level.
3. Place the glass of water on a window ledge and check it each day, observing the water level compared with the position of the rubber band.

Another way to demonstrate evaporation is to put water on two separate sheets of construction paper. Let one sit undisturbed and fan the second one with a piece of cardboard. Notice the results.

Evaporation is the change from the liquid form to the vapour (gaseous) form. The water molecules are still there when the water evaporates, but they are now gas molecules in the air, and not in the glass. Evaporation takes place faster when air is in motion.

Heating water causes it to boil (at 100 ^oC) and evaporate. The cloud you see coming out of the kettle is condensation (water droplets) from the water vapour.