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Lesson Sequence: Day 4

Day 4: Molarity, lab 3.
  1. Class discussion - Comparing the behavior of chemicals in solutions of water.







                            = Cs+                         = Na+
                            = Cl-                         = Cl-


    Question: Will these 2 solutions conduct the same amount of current?

    Rule (Students derive): To obtain the same behaviour of two salts in solution, they must have the same ratio of # of molecules to volume of water.

    Definition: Molarity - a 1 molar (1M) solution of any chemical has a concentration in water of exactly 1 mole per liter of water.

    • Example: to obtain a 1M solution of NaCl
      from periodic table,
      MW of Na = 22.990 gm/mole
      MW of Cl = 35.453 gm/mole
      MW of NaCl = 58.443 gm/mole


      so, to make up a 1M solution of NaCl, dissolve 58.443 grams of salt in
      1.0 liter of water. (This assumes the salt does not contribute significantly to the volume of the solution.)

    • Example: to obtain a 1M solution of KCl,
      from periodic table,
      MW of K = 39.098 gm/mole
      MW of Cl = 35.453 gm/mole
      MW of KCl = 74.551 gm/mole


      so to make up a 1M solution of KCl, dissolve 74.551 grams of this salt in 1.0 liter of water.(This assumes the salt does not contribute significantly to the volume of the solution.)

      Notice that for these two salts you would add different masses of each salt to a liter of water. The # of molecules per liter for each salt, however, would be identical.

      What if you want to make up only 100 mL of 1M NaCl? How would this salt
      solution be made up? (Have class solve)

    Class problem, (finish for homework). Determine the molecular weight (MW) for each compound in the table and then the mass of salt you would add to each volume of water to make up salt solutions at the concentrations indicated at the top of each column of the table.

        1 M solution 0.3 solution
    compound               MW               1 liter     100 mL         1 liter     100 mL
    NaCl          
    Nal          
    NaF          
    KCl          
    CsCl          
    CsBr          
    MgCl2          
    CaCl2          
    SrCl2          
    BaCl2          


  2. Do LAB 3

  3. Homework
    • finish table
    • finish write-up of LAB 3.
DAY 1     DAY 2     DAY 3     DAY 5     Teacher Info



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