Everyone has Problems, but Chemists have Solutions

Kathy Kreidler                 Thornridge High School
                               15000 Cottage Grove Ave.
                               Dolton, IL 60419
                               (708) 841-5180 X 2585

Objectives:

The student will 
1.  relate chemical solutions to everyday solutions.
2.  define molarity.
3.  explain how solutions of different molarities are prepared.

Materials needed:  

Teacher demonstration:

2 packets drink mix                    table salt, NaCl
2 quart pitcher                        balance
2 drinking glasses--different sizes    beakers--different sizes
labelled reagent bottles of            stuffed cloth mole models*
  differing molarities                 one-liter volumetric flask

Strategy:

1.  Have labelled reagent bottles sitting out on the desk.
2.  Following student directions, prepare a pitcher of drink mix, bringing out 
    the terms solvent, solute, solution and homogeneous.
3.  Pour some of the prepared drink into two different-sized glasses.  Ask the 
    students to compare the concentration of solution in each of the three 
    containers.  All concentrations are 1 pack/pitcher.
4.  Ask how a 0.5 pack/pitcher could be made.  Students should realize that the 
    packet must be opened and the amount desired must be weighed out on the 
    balance.
5.  Point out the reagent bottles and explain that terms such as 0.5M and 3M are 
    expressions of solution concentration.
6.  Using a 1 liter volumetric flask, demonstrate how to make a 0.1M solution of 
    sodium chloride, drawing parallels to making a pitcher of the drink mix.
7.  Pour some of the 0.1M NaCl into different-sized beakers.  Ask the students to 
    compare the concentration of solution in each of the containers.
8.  To recap, bring out a 1 liter beaker and several stuffed moles.  Adding one 
    mole gives a 1 Molar solution.  Stuffing in a second mole gives a 2 Molar 
    solution.  With a flourish, separate a third mole at the velcro strip 
    joining the front and back ends and make a 2.5 Molar solution.  
9.  The lesson can be extended by placing stuffed moles in other sizes of 
    beakers and calculating the molarity of the resulting "solutions." 
 
References:

*Weird Science #5 (for mole pattern).  Make one special mole by constructing 
the front and back halves separately and then joining them with a velcro strip.