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Lesson Overview
This activity uses a common and simple science-fair project apparatus for desalinizing water as a means to introduce students to the management of variables in a scientific experiment. Students are given the basic design of the apparatus and asked to devise and carry out experiments to test how three variables affect the performance of the desalinizer.
Student Ability Level and Grouping
This activity is best suited for middle-school or ninth-grade physical-science students or as an introductory lab in a high-school chemistry course. Students should work in groups of three or four in this activity.
Expected Student Background and Skills
Prior to carrying out the activity, students should
- have a conceptual understanding of evaporation, and
- know that water evaporates but salt does not.
Time and Materials Required
Expected time to complete activity: 30 minutes on the first day, and 15 minutes on the second day.
Consumables
- NaCl
- Water
Non-consumables
- 1,000-mL beakers
- 500-mL beakers
- Saltwater solution
- Plastic wrap
- Rubber bands
- Heat lamps
- 50-mL beakers
- 25-mL beakers
- 10-mL graduated cylinders
- Black construction paper
- Scissors
- Adhesive tape
- Electrical conductivity apparatus
Learning Objectives
After completing this activity, students should understand
- the concept of evaporation;
- that water evaporates and salt does not;
- that separations depend on a difference in the properties of the substances being separated;
- what dependent variables and independent variables are in an experiment;
- that only one variable should be changed at a time in an experiment; and
- the important role of a control in an experiment.
In addition, students should be able to
- design an experimental strategy for determining the effects of the three independent variables on the rate of desalination;
- conclude from their experimental results the effects of changing each variable;
- make predictions based on their experimental results; and
- conceive of ways to test additional variables.
National Science Education Standards
Science as Inquiry (Grades 5 to 8 and 9 to 12)
- Abilities necessary to do scientific inquiry
Physical Science (Grades 5 to 8)
- Properties and changes in properties of matter
- Transfer of energy
Physical Science (Grades 9 to 12)
- Structure and properties of matter
- Motions and forces
- Interactions of energy and matter
Earth and Space Science (Grades 5 to 8)
- Structure of the earth system
Science and Technology (Grades 5 to 8 and 9 to 12)
- Abilities of technological design
- AUnderstandings about science and technology
Science in Personal and Social Perspectives (Grades 5 to 8)
- Populations, resources, and environments
- Risks and benefits
Science in Personal and Social Perspectives (Grades 9 to 12)
- Natural resources
- Science and technology in local, national, and global challenges
History and Nature of Science (Grades 5 to 8 and 9 to 12)
- Science as a human endeavor
- Nature of scientific knowledge
Classroom activities are provided through the generous support of the Biogen Idec Foundation.