Changing Salt Water into Fresh Water

Today 5th Graders used their knowledge of the water cycle to create a device that changes salt water into fresh water.

Most of the earth's water is trapped in the ocean.  It is not useable for drinking.  In fact if all the water in the world was modeled by a two liter bottle (2000 mL), 1950 mL would be salt water!

Only 50 mL would be fresh.  This fresh water includes unreachable ground water, lakes, rivers, and streams, as well as glaciers and ice caps.

Taking away all of the unreachable water (in the ice caps and deep underground or trapped in porous rocks) only .5mL of our model would be drinkable water!  Amazing we don't die of thirst!

Today students worked in groups to design a way to turn salt water into fresh water using their knowledge of some very important water cycle words!

Evaporation:  When liquid water turns into a gas and rises.
Water must evaporate out of the salt water, leaving the salt behind.

Condensation:  When water vapor turns into liquid water.
The water vapor must condense to form liquid fresh water.

Precipitation: Water falling in any form.
The condensed water must fall (into a new container hopefully).  The collected precipitation should be your fresh water.

Check out these contraptions:

I think I would want these kids with me on a deserted island!

We also used our knowledge of the water cycle to make  a cloud.

The water cycle

First we evaporated hot water.

Then we put dust in for water to stick to.

Then we cooled the water by putting ice on top.  This caused condensation onto the dust particles and the bottom of the cup.

Then we watched the cloud form in the jar.  The cup and jar began to precipitate!

Of course we had to let the cloud loose and enjoyed watching it rise out of the jar.

Check out another way to make a cloud.  This time I used rubbing alcohol and air pressure changes to create a cloud.

Think about why it works.

This cloud is made by changing the pressure!  When you change pressure you change the temperature.  High pressure- higher temperature.  When I untwist the bottle, I lower the temperature and cause the water to condense on the rubbing alcohol fumes. With a parent, see if you can get the same result!

 (Blue food coloring is in the alcohol so you can see it better.)

This is a great silly science song about the water cycle

Water Cycle by Mr. Davies on School Tube