Water Projects

Learning Objectives:

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

Materials, equipment and/or facilities:

• 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.

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.

PROJECT: Properties of Water

• Working alone or in pairs, students will prepare a project on one of the properties of water.
• Each project will include:
  • One and a half to two pages written (not counting diagrams or bibliography)
    
  • Demonstration

Your demo:

Who else is in your group?

About the Demonstration:
When you go up to present your demonstration:

1. Present your demonstration with minimum explanation.
2. Ask the class questions. See the list on the hand-out for ideas.
3. After the class answers questions, give your explanation of the demo.
4. Relate your demonstration back to the topic of your project.

About the Written Paper

• Staple your outline and rough draft to the back of your good copy.
• Neatness, spelling, and grammar count for the good copy.
• It is important to cover all the areas listed in the outline section (below).
• Start by making an outline. OUTLINE should include:
  1. An introduction on the importance of water and what you are going to write about in your report.
  2. A written explanation of your demonstration.
  3. A detailed scientific explanation of the characteristic of water you have selected. Information beyond your demonstration.
  4. Explain examples of applications (uses) of your water property in everyday life and nature.
  5. A conclusion that sums up what you have stated in your paper.

You must list your sources in a BIBLIOGRAPHY. Format examples:

FOR A BOOK
Author. Title, Publisher, Edition, City of Publishing: Most recent year of publishing.
Smith, Bill. Water's Invisible Skin, Norton and Norton, 2nd edition, Toronto: 1991

FOR AN ENCYCLOPEDIA
Encyclopedia, Edition, Volume, City of Publishing: Most recent year of publishing.
World Book Encyclopedia. 11th edition, Vol.10, New York: 1990

FOR A MAGAZINE ARTICLE
Author, "Title of Article", Magazine, Volume: Number, Year
Jones, Samantha. "Water in the World", Scientific American, Vol.58: No.12, 1989

Evaluation of Written Project:
80% content (depth and coverage)
10% clarity of explanation, organization of information, presentation
5% outline and rough draft
5% bibliography

-Projects (both the demo and the paper) will be due on

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

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

9 - Layering
10 - Supersaturation

11 - Cooling Fan
12 - Changing the Melting Point

13 - Bobbing Mothballs
14 -Different Size Candle Pieces
15 - Levitating Droplet
16 - Weird Grapes

• 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?

C - Saturation and Super-Saturation

• When a solvent contains the maximum amount of solute it can take, it is saturated.
• When there is some at the bottom, it is still just saturated.
• When heated, a solution's solubility increases and it can take more solute.
• If cooled carefully, it will contain more solute than it normally could at the cooler temperature - this is supersaturated.
• Just add a little more solute and all the solute will crystallize out.

PART IV - Phase Changes and Volume

A - Phase Changes of Water

• When most substances freeze, they contract (get smaller).
• Water is special in this way: ice takes more room than the same weight of liquid.
• When ice freezes, the water molecules form crystals that take up a lot of room.
• This means that ice floats instead of sinking.
  -Important for fish, icebergs, lakes.
• At all 3 phases, the water molecule is intact. It does not come apart.
  -The difference between the phases is a difference in vibration of the water molecules.
  -Water needs to be heated to 2700 degrees Celsius before a water molecule will break apart.

• Remember:
  -Ice expands when it freezes and can break pipe and rock.
  -Water vapor is invisible.
  -Clouds are made of liquid or ice droplets.

B - Phases Changes and Heat

• Heat is absorbed and can do one of two things
  
  1. - raise the temperature
  2. - cause a phase change
  
  
• A graph showing the temperature change when ice melts and the resulting water then boils can be described as follows.
  1. - Solid ice is absorbing heat and the molecules are moving faster. The increase in friction between the molecules causes an increase in temperature. Nonetheless, it is still ice.
  2. - Heat of fusion: Heat is being used to change the ice into water. The temperature does not rise.
  3. - Liquid water is absorbing heat and the molecules are moving faster and faster. Increase in friction between molecules causes a rise in temperature.
  4. - Heat of vaporization: Heat is being used to change liquid into vapor. Heat is used to break the bonds between the molecules and not to raise the temperature.
• Remember that the heat needed to cause a phase change in one direction is released when the phase change goes the other way.

C - Phase Changes and Everyday Life

• - Steam radiators: When steam condenses into hot water, the heat of vaporization is set free.
• - Sweating: To evaporate, sweat takes the heat needed for vaporization from our bodies and cools us off.
• - Refrigerators - Liquid freon turns to vapor. This requires heat which is taken from the food in the fridge.

D - Phase Changes and Salt

• -Salt water "prefers" a liquid state.
  • -boils at a higher temperature
  • -freezes at a lower temperature
• -We add salt to boiling macaroni so that water gets hotter before turning to vapor and food cooks faster.
• -We salt ice on the street so we don't have to wait until the freezing point for it to melt.

PART V - Density

1. - What is Density?
   -Measurement of the amount of matter contained in a given volume.
   -Density = Mass = grams Volume cubic centimeter
   -Because one cubic centimeter=one gram of water, the density of one gram of water is:
   1 gram = 1
   1 cm3
   -Density of water is 1g/cm3. This is a reference point for other substances.
   -Specific gravity of a substance is a number that compares the density of a substance with the density of water.
   -Materials with a density greater than 1 will sink.
   -Materials with a density smaller than 1 will float
   -ex
   

   Material Iron Oak Butter Rubber Ice Gold Gasoline

   Density 7.9 g/cm3 0.75 g/cm3 0.87 g/cm3 1.34 g/cm3 0.92 g/cm3 19.3 g/cm3 0.7 g/cm3

   Sink or Float?

2. - Salt and Density of Water
   -Salt increases the density of water (makes it more dense)
   -When salt is added, there are more molecules in the same space
   -When the water gets more dense, the difference between the object floating and the water gets bigger and the object will float higher.

3. - Density Problems
   -Steps to solving problems:
   
   1. Write the basic equation. Density = Mass/Volume.
   2. Substitute the values given in the problem into the formula
   3. Solve for the unknown value.
   1-ex.
   A piece of brass has a mass of 32.0 g and a volume of 3.8 cm3.
   
   Calculate the density of brass.
   D=M/V
   D=32g/3.8cm3
   D=8.4 g/cm3
   
   
   -This equation can also permit you to determine the mass or the volume if you're given the other two values in the equation. (Solve for M or Solve for V.)