Water Cycle - Oceans (4)
Post Lab 

   
OBJECTIVES:
  •  Distinguishing bodies of salt water.
  • Comparing the properties of salt and fresh water.
VOCABULARY:
  • electrolyte
  • fresh
  • hydrogen
  • oxygen
  • seawater
MATERIALS:

Students use a worksheet to compare the world’s oceans.

BACKGROUND:

The Earth's surface is 71% water and 97% of that water is sea water,  while only 3% is fresh water. One of the most significant chemical properties of water is its ability to be a solvent.  The liquid can hold in solution an exceptionally wide range of substances, including electrolytes (salts, which dissociate into ions in aqueous solution) and particulate matter small enough to remain suspended in solution.  

The major inorganic solutes are the positive ions of sodium, potassium, calcium, and magnesium and the negative ions, chloride, sulphate, and bicarbonate/carbonate. When the total concentration of all these ions (i.e., the salinity, or salt content) is less than 3 grams per liter waters are regarded as fresh. Most fresh waters have salinities less than 0.5 gram per liter and are dominated by calcium, magnesium, and bicarbonate or carbonate ions.  Salt waters are defined as those that have salinities greater than 3 grams per liter.

PROCEDURE:
  1. Review the properties of sea water and how it differs from fresh water.  You might want to introduce the information in the following manner:

Fresh Water

Salt Water

  • Not an Electrolyte
  • pure hydrogent and oxygen
  • less dense than salt
  • "new" water (created recently)
  • Electrolyte
  • chemically diverse
  • more dense than fresh 
  • "old" (been in the system for a long time)
  1. Next have the students do the activity on the lab sheet.  Have them color the land differently from the water and then have them label the information.  Have available the inflatable globes that are used in other portions of this program.
        
  2. ANSWERS: 
  1. 70-71%
  2. on map
  3. This map emphasizes the oceans, not the land.  A Mercator projection makes it look like there is more land.  This map is closer to a globe.

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