Mixtures

OVERVIEW:
Variables affecting the rate of the dissolving of a substance (solute) in water (solvent) are discussed and observed through experimentation.


PURPOSE:
Students will be able to test/experiment with several variables, against a control, to observe the different rates that a solute (sugar) dissolves in a solvent (water) to form a solution.


OBJECTIVES:

1. Students will observe that movement of the solute in the solvent increases the rate of dissolving, as compared to the control.
2. Students will observe that the solute, when broken into smaller parts, will dissolve in the solvent faster, as compared to the control.

RESOURCES/MATERIALS:
For each group: piece of paper, three clear drinking glasses, one spoon, paper towel, three sugar cubes.

ACTIVITIES AND PROCEDURES:
Students form groups of three. Each member has a job--recorder, "go-for," and taskmaster.
First, the recorder folds a piece of paper in half, from top to bottom. The top half is used to record predictions, the bottom half is to record observations. He then separates each half into thirds (rows). The recorder folds the paper in half, left to right, then in half once again (fourths) to obtain four columns. He writes the members' names in the first column, in both top and bottom halves, one name per row. At the top of the second column he writes "control." At the top of the third column he writes "with motion." Finally, at the top of the fourth column he may write "smaller pieces."
Secondly, the "go-for" obtains three clear glasses half-full of water of the same temperature, three sugar cubes, spoon, and paper towel. Taskmaster makes sure all procedures are followed. He may do everything himself or delegate jobs to others. He is responsible for quieting group members during teacher instruction.
Now, each group has before it a control (glass with sugar cube), a motion glass (glass with sugar cube and spoon), and a small piece glass (glass with broken sugar cube). Each student should make a quick prediction as to what might happen when sugar is placed in each glass simultaneously. The emphasis should be on the order to which glass will have a solution first, second, and third. The recorder should record these predictions. At the same time, the sugar should be placed in the glasses and the movement glass should have constant stirring until a clear solution is obtained. All should observe and the recorder may then list the observations of each member. Of course, there are other variables that students may want to try: heat, heat and movement, pieces and movement, etc.

TYING IT ALL TOGETHER:
Students should be able to find ways to obtain mixtures more rapidly from the exposure to the variables discussed and observed in this lesson: from mixing frozen orange juice for breakfast, melting things for mixtures in cooking (butter), stirring ingredients for batters, to putting out a campfire (stirring the ashes with water). The students may think of other everyday situations with mixtures that may use the experimented variables.

\EVALUATION