Water Cycle - Oceans (4)
Lab 

   
OBJECTIVES:
  • Discovering that salt water is an electrolyte.
  • Reviewing the properties of salt water.
VOCABULARY:
  • chloride
  • electrical circuit
  • electron
  • electrode
  • electrolyte
  • ion
  • sodium
MATERIALS:

Students experiment with an electrolyte.

BACKGROUND:

Water is a compound that has strong "bonds" among its constituents.  In other words, it is difficult to break apart the hydrogen and oxygen atoms without some sort of energy input.  "Salts," on the other hand, usually have weak "bonds" and the atoms of salts can easily be separated into its appropriate ions.  When a salt, like sodium chloride (table salt) is dissolved in water the sodium and chloride separate temporarily.  The sodium atom will become a positively charged ion and the chloride atom will become a negatively charged ion.  An ion is an atom or group of atoms that has a negative or positive electric charge.  Negative ions are formed by atoms gaining electrons, and positive ions are formed by atoms losing electrons.

Substances that conduct electric current are called electrolytes.  They are formed  as a result of a  dissociation into positively and negatively charged particles called ions, which migrate toward and ordinarily are discharged at the negative and positive terminals of an electric circuit, respectively. The most familiar electrolytes are acids, bases, and salts, which ionize when dissolved in such solvents as water. Many salts, such as sodium chloride, behave as electrolytes when dissolved in water.  Pure water will not behave as an electrolyte.

PROCEDURE:
  1. Review with the students that fresh water is basically pure "water" whereas salt water has many other elements dissolved in water.
       
  2. Students will discover in this lab that the ions in the water make salt water an electrolyte.  An electrolyte is a nonmetallic electric conductor in which a current is carried by the movement of ions.  
      
  3. Go over the lab set-up with the students as diagramed on the students' sheet.  The battery can be a six volt or smaller, depending on the type of bulb you have.  (Remember if the voltage is too high it will burn out the light bulb).  An electrode refers to whether a current enters or leaves a conductor
      
  4. Ask the students to determine if the light bulb will glow brighter if more salt is added.  Yes, but there is a maximum point that the bulb will reach and will not glow any brighter.  The salt acts as an electrolyte, making electricity transfer more efficiently.  Fresh water has no ions that can make it act as a conductor.  Have the students record their data on the graph.  Then when you discuss the experiment with the students have the student write a summary of the class results.

[Dictionary]
  [Back to Water Cycle Grid]  [Back to Oceans (4)]