Water Cycle - Oceans (3)
Pre Lab 

   
OBJECTIVES:
  • Comparing water's states of matter. 
  • Discovering an ion.
VOCABULARY:
  • covalent bond 
  • dissolve
  • fresh water
  • ion
  • ionic bond
  • salt water
  • solvent
MATERIALS:
  • worksheet 

Students use a worksheet to learn about an ion.

BACKGROUND:

Water is a transparent, odorless, tasteless liquid.  It illustrates 3 states of matter in the form of ice, steam, and water.  The form it takes depends on the temperature.  At low  temperatures, the molecules do not move around as much and form a crystalline structure that is rigid, and a little larger structure in the liquid state, and very open in the gaseous state.

Water has a very large heat capacity, meaning that it can absorb a great deal of heat without becoming extremely hot.  This fact makes the ocean a large reservoir of heat, that greatly affects the overall weather and climate patterns of the world. 

The students should remember from last week, that the hydrogen and oxygen "bond" together, or "hold hands."  The bond is very strong and is called a covalent bond. Because the bond is so strong, water is considered a universal solvent, since many things dissolve in it. Water is a special type of covalent bond called a hydrogen bond.  Salts on the other hand hold hands very weakly and break up very easily in water.  This is called an ionic bond.  

The break up of salts in water causes the water to have the ions of that salt.  For instance,  table salt is sodium chloride (NaCl).  When it is dissolved in water it turns into a positive ion of sodium (Na+) and a negative ion of chlorine (Cl-).  Dissolving does not mean that the compound breaks into its elements.  If that was the case, sodium, the element is reactive with water and chlorine is a deadly gas.  It is important to use the correct terms early in a studentís education, so they don't get confused later on. 

PROCEDURE:
  1. Introduce the term ionic and covalent bonding as a way that different compounds are held together. Ionic bonds are not as strong as covalent. On the worksheet have students write a sentence that covalent is a strong bond and ionic is weak or not as strong. You might want them to think of a "poetic" way of writing it. "Water is held together by very strong glue." "Salts are weak, so they break apart easy."   
      
  2. On the worksheet have them draw a water molecule after you go over the water molecule pictured below.
  1. In the second picture it shows the different ions moving around freely into the "Ion Club." So imagine the club as the water molecule which the different compounds break up into ions and move around. If the club goes away, the ions would go back together to form the characteristics of their compound. So sodium chloride or table salt would become cubic and white again without the water. This is a silly example, but it is important to show them what an ion is. Have the students write a sentence of their interpretation of the "Ion Club."

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