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To Be Salty Sea Ice Or Not To Be Salty Sea Ice
An Introduction To Sea Ice At The Polar Regions
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Author Contact Information
Sandra Kolb, Education Consultant, Poulsbo, Washington
Kolene Krysl, Westside Community Schools, Omaho, Nebraska
Larry Rose, Pleasanton Middle School, Pleasanton, California
Wendy Slijk, La Costa Canyon High School, San Diego County, California
Overview
Grade Level/Discipline
Middle school levels 6-8 in Earth, Physical and Life Science with applications to mathematics.
National Standards
Content Standards 5-8 Science:
Content Standard A-Students should develop
Abilities necessary to do scientific inquiry
Understand about scientific inquiry
Content Standard B-Students should develop an understanding of
Properties and changes of properties
Transfer of energy (possible extension activities)
Content Standard G-Students should develop understanding of
Science as a human endeavor
History of science
Pre-activity set-up
What should the facilitator do/get before the activity starts?
Assemble materials.
Decide whether there is an available freezer at school or if this activity needs to be done as a homework assignment.
Develop a rubric.
Materials
Clear plastic cups (3 to 5 per individual or small group) and/or paper cups of various types and sizes.
Salt: approximately 1/2 cup per individual or small group.
Distilled water (preferred if available): 1 liter per individual or small group.
Notes to teachers: If freezer space is limited, popsicle trays or ice cube trays may be used. Have a variety of materials related to measurement available for student use (i.e. rulers, cups, balances, graduated cylinders, etc.). Thermometers might be required for extension experiments for students wanting to extend this experience.
Time Frame
Two 50-minute class periods or one 50-minute class period with overnight homework activity.
Engagement and Exploration (Student Inquiry Activity)
Opening discussion and predictions (15-20 minutes). Encourage students to journal questions, thoughts and predictions in writing and/or drawings.
Hold a class discussion asking what types of solutions can freeze:
Can fresh water freeze?
Can salt water freeze?
What other types of solutions might freeze?
Distribute the student materials.
Explanation (Discussing)
Individuals or small groups design their experiment and form a plan that must be approved by the teacher prior to beginning.
Give the students the remainder of the class period to begin their experiment plan.
Notes to teachers: Since the students will be designing their own experiments their procedures will vary. Ideally the procedure should show a "fair experiment".
For example, students may use several cups, perhaps three to five, of the same kind with equal amounts of water in each and amounts of salt progressing from none to one to several dry metric measures (all students will use the same metric unit). Students need to be sure that the salt dissolves completely when they add it to the water. These cups should then be placed in a school freezer, if available (or the entire experiment can be done at home as a homework assignment). After a predetermined time period, the students will look at their cups and make observations (write or draw in their journals) about the state of the salt water.
Elaboration (Polar Applications)
Note to teachers: For an additional activity, ask students to put the salt in the water but not to stir it. Let it fall to the bottom and sit. Will it dissolve? How long will it take? Does the dissolution rate vary with water temperature? Will the water with initially undissolved salt freeze in a different manner from a sample with an equivalent amount of water and dissolved salt?
Possible student extension investigations--
Design an inquiry activity investigating heat transfer as polar sea ice melts.
Explore how sea ice acts as a thermal blanket for Polar Regions.
Discover how salinity decreases as polar ice ages.
Investigate how living phytoplankton frozen in polar sea ice acquire nutrients.
Exchange (Students Draw Conclusions)
Discussion questions for students:
After seeing the results of your experiment and your classmates' experiments, would you predict that it is possible to put so much salt in water that no matter how cold it gets the water won't freeze?
What else could we try in water other than salt to see its effect on freezing? (Students may offer sugar or pepper, alcohol, other salts.) Allow students the latitude to try all manner of things within the bounds of home and lab safety. Emphasize that they must check with the teacher before trying any new experiments.
How much salt is dissolved in ocean water? Do you think it is the same worldwide? How about near where rivers enter the ocean, or in oceans near deserts where there is a lot of evaporation?
Find out if the ice in your cups is salty or fresh. Design an experiment to find out.
Notes to teachers:
Tasting any reagents is unsafe lab procedure. Students will suggest that this is the way to do it. Do not allow tasting. A suggestion is that this can be accomplished through evaporation and looking for any salt crystals left behind. A way to do this is to take a drop of water from the melted ice and place it on a slide to evaporate.
New ice made from salt water will have an initial salinity roughly 50% of that of the seawater from which it forms. Then, as polar sea ice ages, more and more salt is lost from the ice as it drains out under the influence of gravity or is flushed out by melt water in summer.
Evaluation (Assessing Student Performance)
Rubric to assess:
Design of student's experiment and their data (diagram and description).
Conclusion statement about the connection between salt water freezing and sea ice.
Student visual for classroom sharing.
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