Water : The Universal Solvent

advertisement
Water : The Universal Solvent
This project is designed to be used with the ChemCom water unit, Section C.
Investigating the Cause of the Fish Kill
Cathy Erickson,
Newburyport High School, Newburyport, MA 01950
[email protected]
Paula Flanagan
Hingham High School
17 Union St.
Hingham, MA 02043
[email protected]
Introduction
In Part A of the ChemCom Water unit, students are introduced to water as a limited
resource. Part B introduces the physical properties of water, as well as the concepts of
elements, compounds and mixtures. Part C introduces the ideas of solubility and
solubility curves. The exercise that we have created helps students to visualize the
critical characteristic of the water molecule that allows it to be such a good solvent,
namely its polar nature.
The SMD program will be used to visualize the process of solvation, as well as to
quantitate the effect of temperature on the rate of dissolving. Using the Water program,
students can manipulate the water molecule in three dimensions and view the process of
dissolving at the molecular level. By viewing the water molecule both by itself and as it
dissolves an ionic compound, students should be able to get a better understanding of
how the parts of the water molecule work to pull apart an ionic compound.
This exercise is intended to motivate and stimulate curiosity about the molecular world
and its activities.
Intended Audience
In general, the ChemCom curriculum is used as a first year high school Chemistry course.
Students exhibit a wide range of motivation, curiosity, interest and abilities.
This activity on water and dissolving may be appropriate for Physical Science,
Oceanography, or Environmental Science at grade levels 8-12.
Students at all levels seem to have difficulty in conceptualizing a particulate view of
matter that explains observed natural phenomena. This activity should provide a strong
foundation for rich discussion and greater understanding of this concept as it relates to
water’s ability to dissolve many substances.
The Massachusetts Science and Technology/Engineering Curriculum Frameworks
document, adopted in May 2001 is closely aligned to the National Science Education
standards and ChemCom, a project of the American Chemical Society, has made a strong
effort to align their curriculum with those national standards.
This year’s graduating class (2003) marks the first year that passing the MCAS test in
Math and Language Arts will be required for graduation. It remains to be seen how
strictly this state dictate will be enforced upon individual school districts which have
traditionally been very independent. Currently, Massachusetts teachers of science do not
have a MCAS test for graduation. Tryout questions for “end of course” exams in Biology,
Chemistry, Earth Science and Physics were taken by students this past year. It is
predicted that the actual exams will be available around 2005, with graduation
requirement of passing 2 science MCAS test necessary by 2008. As this is an expensive
and rather political undertaking, most science supervisors are adopting a wait and see
attitude concerning the ramifications of the MCAS test on the curriculum.
Adjustment/Adaptation
The activities that we have created could be performed across a broad spectrum of
classroom management strategies: from structured, teacher led, to student centered with
teacher facilitation, to totally independent learning.
As teachers and students gain ease and understanding of the various models found in
SMD and Water programs, they can devise their own questions and explanations.
Some ideas for enrichment:
Simulab #1. Rate of Dissolving. Use excel or other graphing program to further analyze
the Time vs. Temperature curve. Why is this a curve rather than a straight line? What is
going on at the molecular level that makes this process non-linear?
Simulab #2. The Structure of Water. This would be a good place to introduce hydrogen
bonds. We only used two molecules. With more molecules, there would be more
interaction, and in the mixed view, many questions could be posed as the molecules are
subjected to different conditions of density and temperature. With more molecules, the
hexagonal arrangement of the ice could be explored further.
Simulab #3. Dissolving a Salt in Water. We did not address the concept of hydrogen
bonds in dealing with dissolving. This could be easily incorporated into the questions
that the student is asked, as they appear like green rays in the mixed view. Other ions
could also be added, and predictions made about the outcome as compared to what
happened with sodium chloride.
Placement in the Curriculum
These simulab activities were designed to be implemented within the existing ChemCom
water unit. The fourth edition text places quite a bit of emphasis on Modeling Matter.
The VMD, Universal, and Water programs enhance the students’ understanding and
experience. Please refer to the Introduction and Instructional Activities for an overview
of how this curriculum effort may be implemented.
Time
We suggest spending one 90 minute class period or two 45 minute class periods to
include the 3 simulation lab activities.
Resources
ChemCom text, 4th edition. W.H. Freeman and Company.
Wet lab “ Constructing a Solubility Curve” Materials list is found on pg. 49 in that text.
W. H. Freeman also has a web site to support ChemCom teachers and students :
www.whfreeman.com/chemcom.
A CD-ROM is available with a variety of interactive student features, including
animations, simulation, and interactive Q & A.
Electronic Equipment
Ideally, the simulabs should be done with 2-3 students per computer.
Goals and Objectives
From the Mass. Science and Technology/Engineering Curriculum Framework:
Solutions:
7.1 Describe the process by which solutes dissolve in solvents.
7.2 Identify and explain temperature as a factor that affects the rate of dissolving
From ChemCom:
Use the polarity of water molecules to explain water’s ability to dissolve ionic solid.
Instructional Activities
Lesson one: Intro to Solubility terminology and a solubility curve. (C.1) and Building
Skills 5
Lesson two: Solution concentration (C.2) Building Skills 6 and pre-lab for next class lab.
Lesson three: Wet Lab: Constructing a solubility curve (C.3)
Lesson four: Dissolving Ionic Compounds (C.4) discussion with simulabs
Lesson five: Other possible causes of the fish kill: heavy metals, pH
Lesson six: Dissolved Molecular Substances
Lesson 7: Dissolved gases
Lesson 8: Data Analysis
Assessments
Embedded assessments---the worksheets provided for the simulabs incorporate aspects of
formative assessment that demonstrates students’ basic understanding of water’s structure
and its dissolving capability. Simulab #1 involves a graphing exercise to assess students’
abilities to perceive trends in data.
Homework assignments
Reading guides
Your Turn from text: Solubility and solubility curves, Describing Solution Concentration
Pre Lab and Lab Report : Solubility Curve, Solvents
Formal assessments including culminating projects
Section Quiz, Unit test, and Making Decisions: Data Analysis
Lab Reports will be assessed using teacher generated scoring guides
Download