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Main Curriculum Tie:
Background For Teachers:
The amount of water vapor in the air varies with the time of day, weather, and location. Air with lots of water in it is said to be humid. Air without much water in it is said to be dry. How much water is in the air can be measured in a humidity chamber. Cobalt paper is an indicator for a humidity chamber and is blue when in dry air and turns pink in humid air.
Water changes its states based on the energy of its molecules. If their
energy is low they will exist as solid ice, with more energy they exist as liquid
water and the highest energy water molecules exist as a vapor or gas. In liquid
water, when some of the liquid molecules get enough energy, they can escape
the liquid phase and become a vapor even if the water isn't boiling. This is the
process of evaporation. When vapor molecules of water cool their energy
decreases and they change from the vapor state to the liquid state. This is
called condensation. After precipitation, some of the water seeps into the soil
and some of the water runs off over the land and into bodies of water such as
rivers and lakes.
Intended Learning Outcomes:
I. Humidity Chamber
What is happening to the warm water in the container? The warm water has some water molecules moving so quickly that they leave the liquid state and become a vapor.
What is happening to the air inside the container? As the water evaporates it makes the air inside the container humid.
What caused the paper to turn pink? The water in the vapor causes the cobalt paper to turn from blue to pink.
What were we testing in this experiment? We were testing whether water was evaporating inside our chamber.
Take the pink paper out of the chamber and it will return to blue after it is left out for a few minutes. This paper can be reused.
II. Evaporation - The process in which water changes from a liquid to a vapor.
What happened to your spots? They should disappear.
Where did the water go? The water changed from a liquid to a vapor. The water molecules are now floating around the room.
The hair dryer is acting as the warm sun and wind. This warmth gives more molecules the energy they need to leave the liquid state and move into the vapor or gas form. This is called evaporation.
III. Condensation - The process in which water changes from a vapor to a liquid.
What do you see forming on the top of the mirror above the ice? Students should see a fog of water droplets forming.
Where are these water droplets coming from? Did they come from the ice? Students may think the water droplets are moving from the ice, through the mirror to the other side. Be sure and explain that this is NOT happening. The water that is forming on top of the mirror is coming from the air around the mirror. As the air cools above the mirror, some of the water molecules in the air slow down enough that they leave the vapor form and become a liquid on top of the mirror. This process is called condensation.
What forms on the mirror as you breathe onto it? You should see a large amount of water droplets forming on the mirror because the water in your breath is undergoing condensation and forming water droplets on the mirror.
IV. Evaporation and condensation
Why is this happening? When you squeezed the bottle, you caused pressure and this pressure caused the liquid water to evaporate. When you released the pressure the water vapor went through condensation and formed as liquid droplets in the air in the center of the bottle. You change the water form a vapor to a liquid and back to a vapor each time you squeeze and release the bottle.
V. Precipitation – When water that has undergone condensation in a cloud falls to the earth as rain or snow.
What represents the ‘clouds’ in this experiment? The water droplets forming under the Pyrex dish represent a cloud.
What is precipitation? Rain
Why is this happening? Small misty drops condense on the underside of the
bowl of ice. When the drops collide with each other they form bigger and bigger
drops of water and represent clouds. When the clouds get enough water in
them that they can no longer hold it, the water droplets drop down as rain onto
the earth. If the temperature is cold enough, they drop as snow.
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