Water Projects

Summary: Students will present a discrepant event demonstration to the class and will prepare a written project about one of the properties of water.

Learning Objectives:

1. Students will explain a discrepant event demonstration and relate it to a property of water.
2. Students will describe several aspects of a property of water in a written project.

Materials:

• Materials needed by each groups of students are listed on their Demonstration hand-outs.
• The following is a master list of materials needed for each class. This includes both the practice run and the actual class demonstration.
• 10 beakers
• 1-large shallow plastic tray
• 3 eyedroppers
• 75 pennies
• 3-4 mothballs
• crushed ice
• 3 thermometers
• dish detergent (for 3 groups)
• 1 shaker of pepper (ground)
• pepper (whole kernels)
• 30 cm thick cotton string
• masking tape
• 50 ml cooking oil (shared by 2 groups)
• 40 grams of table salt
• 1 sewing needle
• 2 Alka Seltzer tablets
• 2 carnations (or celery)
• 3 pieces of wax candle
• 2 cans of clear carbonated soda
• 4 grapes
• 1 heating plate or other heat source
• 2 plastic pails
• 1 fabric towel
• 1 electric fan
• 1 set of capillary tubes
• sodium acetate solution (see Notes)
• 1 small spatula
• 1 Erlenmeyer flask
• 100 ml rubbing alcohol (shared by 3 groups)
• 1 clear plastic transparency
• 2 pieces of paper
• 1 pair scissors
• 1 petri dish
• 2 drinking glasses
• 1 tall glass jar
• 1 paper clip
• red & blue food coloring (shared by 3 groups)
• 1 sharp knife or scalpel
• safety gloves (enough for one group)
• safety goggles (enough for one group)

Sequence and duration of each part of lesson:

• 2 class periods:
  Working in assigned groups, students will prepare projects on one of the properties of water. Each project will include a written component and a demonstration for the class. The details of the projects are outlined in the student Water Project hand-out. (Appendix A) . Students will need to practice their demonstration before presenting it to the class. Descriptions of the student demonstrations are in the Demonstration hand-outs (Appendix B). A transparency useful in assigning groups can be found in Appendix C.
• 3 class periods:
  Students will present their demonstrations to the class. Many of these can be presented as discrepant events, so presenters should be warned not to give away the solution before asking the class to propose explanations. Presentations will be grouped by topic: capillary attraction, surface tension, solubility, density, and phase changes. After each set of presentations, the teacher will present the corresponding section of notes. Content notes are in Appendix D.

Total Duration: 5 class periods

Evaluation: Written projects will be evaluated based on the criteria in the Water Project student hand-out.

Presentation of demonstrations will be evaluated based on the Demonstration Evaluation Form (Appendix E).

Notes

1. To prepare for the next lesson plan, the total number of students studying each of the four following topics should be relatively equal:
   1. Surface tension
   2. Capillary attraction
   3. Solubility and phase changes
   4. Density.
   • For example: In a class of 32 students, even though some groups might have 2 students while others have 3, there would be a total of 8 students studying each of one the four topics. This will ensure even distribution of "topic specialists" in the next lesson.
2. The sodium acetate solution (super saturation demonstration) will need to be prepared in advance by the teacher. See the supersaturation demonstration desciption in Appendix B for details.

1 - Boat Drive
2 - Quick Pepper
3 - Pennies
4 - Needle

5 - Colorful Carnation
6 - Towel climb
7 - Capillary Tubes
8 - Creative Water Transfer

• the tendency for molecules of the same substance to stick together.
• stronger between molecules in solid, than in liquid.

B - Water's Invisible Skin

• Below the surface all cohesive forces are balanced.
• At the surface, molecules are only attracted by other water molecules beside and below.
• This causes molecules at the surface to bunch together and form a "skin" on water.

C - Soap and Surface Tension

• Soap reduces surface tension by breaking the cohesive forces of water.
• When soap is added to a plate with pepper, the pepper sinks because the surface can no longer support the weight of just pepper!
• When soap is dropped onto water, a paper "boat" will move because the cohesive forces behind the boat are weakened while the ones in frot remain strong. The boat is then pulled forward.

PART II - Capillary Action

A - Adhesion

• Is the attraction between molecules of two different substances.
• Some forms are more obvious: tape + skin, glue + paper, but also: water + skin

B - Capillary attraction

• When the adhesive forces between the glass and the water are stronger than the cohesive forces between the individual water molecules, water will be more attracted to the glass.
• Water will then rise up the glass sides.
• In a smaller glass tube, there is more glass compared to the amount of water in the tube and so the water rises up the tube.
• Capillary attraction is the rising of water up small openings.
• This permits water to rise up the spaces between threads in a dish cloth.

PART III - Solubility

A - Terms

• Solution=mixture combined on a molecular level.
• Suspension=mixture combined at a particulate level.
• Solvent=Substance in greater quantity that takes in the other ex water.
• Solute=Substance in lesser quantity that is taken in by the other substance ex sugar.
• Solubility=how readily a substance will dissolve in a solvent.
• Water is known as the "universal solvent".

B - Polarity

• Solubility depends on polarity.
• Polarity means that one end of the molecule tends to be negative while the other is positive.
• Water, one the whole, is a neutral molecule. The charges are not evenly distributed.
• Polar substances will dissolve in polar substances.
• Non-polar substances will dissolve in non-polar substances.
• They will not dissolve in the opposite.
  -ex of polar: water, alcohol
  -ex. of non-polar: oil, benzene
• Will benzene dissolve in oil? water? alcohol?