Estuary = Salty + Fresh
Are the waters around New York City salty or fresh? (Answer - a mixture! called an "estuary"). We are about to investigate some of the properties of this mixing of waters.
Materials
- Notebooks & pencils!
- Water
- NaCl
- Potatoes (1 piece per group)
- Cups (clear plastic), 2 per group
- (If available) graduated cylinders
- Food coloring
Activities
- Each group gets 2 cups, each half-filled with water (preferably of exact measured amount), NaCl to put into one cup, and a potato to put into the other
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- Put potato in one cup - write down observations
- Put salt in the OTHER cup, and work on dissolving it completely (alternatively, I provide saturated NaCl solution, prepared in front of class)
- (Possibly) have some or all groups put food coloring in their salt or fresh water
- Students in group take turns adding small amounts of salt water to potato glass, til it "levitates"
- Record how much salt water was added to achieve this
Wrapup
A new way of telling salt from fresh water has been discovered! We see that salty water sinks below fresh water, and that it is better at floating things.
Discuss why this is important in local waters.