Grade:
Time:
Topic:
Concept:
SOL: 5.6
The student will investigate and understand characteristics of the ocean environment. Key concepts include
geological characteristics (continental shelf, slope, rise);
physical characteristics (depth, salinity, major currents);
biological characteristics (ecosystems); and
public policy decisions related to the ocean environment (assessment of marine organism populations, pollution prevention).
Rationale:
Goals:
Cognitive Objectives: The student will orally explain the desalination process with 100% accuracy. The student will be able to answer 3 out of 4 questions about the desalination process and its application.
Psychomotor Objective: The student will create a small solar powered still, exercising fine motor skills and coordination.
Affective Objective: The student will understand that desalination is important to parts of the world that do not have rich water reserves.
Content:
Virginia SOL 5.6
Characteristics of water
Properties of solutions
Early understanding of molecules
Application of desalination on the world scale
The student will understand how a solar still works and will be able to apply its use by making a small model. The student will understand that although saltwater is a solution, the solution can be separated quite easily by using the sun’s energy. The student will orally state the implications solar stills have on the world and will orally suggest how a solar still works.
Materials:
pebbles
tablespoon measure
rubber bands
Saran Wrap (plain)
clear plastic cups
black construction paper
tablespoons
salt
small plastic cups
Procedure:
The student will follow the teacher’s directions and create a small solar still. After the still has been completed, the teacher will bring out a solar still that has already been in sunlight for one or two days. The teacher will ask,
“Who would like to taste the water that is in my small plastic cup?”
The child will taste it.
After the child tastes the water, the teacher will ask,
“Does the water taste salty?”
Probably not.
The teacher will ask the class,
“What do you think happened in this solar still that made water end up in my small cup? And why doesn’t the water taste salty?”
The students will offer suggestions, and the teacher will write all of them on the board.
As the children make sense of the experiment, the teacher will explain more about their correct inferences and give more information about the properties of the saltwater solution. The saltwater is a solution, so the salt molecules are binding with the water molecules and forming a completely new substance. This means that the salt and water are connected in a way that cannot be broken by filter paper, whose holes are too large to separate the salt from the water.
The sun provides heat energy that is strong enough to break the bonds between the water and salt, however, and the sun continues to power the evaporation of the water. When the water evaporates as high as the saran wrap, it condenses. We wanted to collect the desalinated water in a cup, so we placed a pebble in the middle so that the water would slide down the saran wrap and land in our cup.
“Now, who can tell me why we would place black paper underneath our solar still?”
(Black absorbs light, white reflects it; so the fresh water will be collected faster if black is underneath the still)
Are solar stills like the ones we made useful for anything? Where might they be useful? As the children offer ideas, the teacher records their responses on the board. When the children are finished, the teacher will show them a solar still website and talk about the place (near the desert) where this solar still is being tested.
Closure:
One student will be asked to put everything away (desks, materials) that the class moved and the teacher will ask everyone else to put away their things.