Water Cycle - Oceans (1)
Post Lab 

   
OBJECTIVES:
  • Exploring how the oceans became salty.
  • Discovering the components of salt water.
VOCABULARY:
  • elements
  • erosion
  • evaporation
  • oceans
  • salt
MATERIALS:

Students use a periodic table to look at what is dissolved in seawater.

BACKGROUND:

Why are the oceans so salty?  Rain on land causes rivers to wash salt minerals from the land and carry them to the oceans.  Rivers not only carry salts to the ocean but also many other elements.  In fact, the oceans contain gold and silver!  If you calculate how much salt there is in the ocean, there would be enough salt to give millions of boxes of salt to each person living in the United States.  That's a lot of salt!  Salt is a very important commodity to people around the world.  Before refrigerators, people had to salt their food in order to preserve it.  Salt is important for preserving food and organisms need a balance of salt in their bodies in order to stay healthy. 

PROCEDURE:
  1. Compare the periodic table placemats with the elements that are in seawater figure. Students can then discover the components of salt water. Go over what each of the major constituent symbols including:
Na = sodium
Mg = magnesium
K = potassium
Ca = calcium
H = hydrogen
C = carbon
O = oxygen
S = sulfur
Cl = chlorine
Br = bromine.


Elements in seawater.

  1. Use the worksheet to illustrate that salt water is made during the movement of water on land. The diagram shows areas where salt is added to the oceans by volcanoes, water erosion of the land, and evaporation of pure water which leaves the salts behind.
      
  2. ANSWERS: 
    1. Clouds do not have salt in them. Only water can evaporate.
    2. Yes, large seas and old lakes have salt in them. Mediterranean Sea and Salt Lake are just a few. Students need to look at the globe.
    3. Sources of salt: volcano and land; evaporation is occurring over the water; erosion is occurring on land and in parts of the ocean that moves.

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