Water Ya Know About Dat?

Category: cooperative learning, reading activity

Learning Objectives:

1. Students will master the following terms as they relate to water: polarity, surface tension, capillary attraction, solubility, density.
2. Students will describe the relationship between polarity and 3 properties of water (surface tension, capillary attraction, solubility)
3. Students will describe the relationship between density and phase changes in water.
4. Students will construct a concept map summarizing 5 properties of water (surface tension, capillary attraction, solubility, phase changes, density)

Materials, equipment and/or facilities:
One copy of the Reading Seminar hand-out for each student.
Deck of playing cards.

Sequence and duration of each part of lesson:
Duration: 1 - 1.5 class periods (Depending if Individual Questions are completed in class or are assigned as homework.)

Sequence: If this lesson is being used independently, students will determine their "specialty" area in one of 4 topics, based upon the card they choose randomly when the groups are being made.

If being used in conjunction with the Water Project lesson, students will have previously selected and studied one of the following topics: surface tension, capillary attraction, solubility, phase changes, or density. Having completed a project on one of the five properties of water studied, each student will be considered a "specialist" in his/her project subject. To reduce the number of specialists, solubility and phase changes will be combined into one subject area. Students will be placed in groups of 4, with each subject represented by one specialist. That is to say, a group will consist of one person who did their project on surface tension, another who did capillary attraction, a third who studied either solubility or phase changes, and a fourth who did their project on density.

To make the groups, use a deck of playing cards. After putting the cards in order, reduce the size of the deck so that there is one card per student; one quarter of the cards should come from each suit and the same numbers should be represented in each suit. For example, if there are 32 students in the class, the reduced deck will consist of the ace through 8 of each suit. Each suit will represent one of the specialty subject areas (surface tension=spades, capillary attraction=hearts, solubility/phase changes=diamonds, density=clubs)

If using this lesson plan independent of the "Water Projects" lesson, students simply select a card randomly from the reduced deck. The suit of their card reveals the set of questions they will answer independently. The number of their card is their group number.

If using this lesson in conjunction with the Water Projects lesson, students select a card randomly from the suit which represents the topic about which they wrote their Water Project. For example, all the surface tension specialists will randomly select a "spade" card. All the capillary attraction specialists will select a "diamond" card and so on. To assemble the groups, use the number of the cards as the group numbers. This will ensure groups of 4 with all 4 specialty subject areas represented.

After completing the reading independently (Appendix A), students will answer the individual questions that correspond to their specialty subject area on the Reading Seminar Student Worksheet (Appendix B). Students will then share the information about their subject area with the rest of their group. The group will answer the "Group Questions" together and create a concept map. See Appendix C for a sample concept map.

Evaluation: Evaluation will be based on the Reading Seminar student hand-out (Appendix A)

Water Reading Seminar

When electrons are not shared equally in a covalent bond, the molecule is described as polar. This means that while water molecules are neutral as a whole, one end of the water molecule tends to have a positive charge while the other has a negative charge. Each end of a water molecule is attracted to the opposite charged end of another water molecule. Consequently, water's polarity is responsible for the "stickiness" or cohesion between the molecules.

Cohesion of water causes capillary attraction, the ability of water to move uphill in small spaces. Water will move up the fibers of a plant because of cohesion. This force helps plants get the water they need to survive. In addition, it moves water upwards in soil. Cohesion of water also causes surface tension, water's invisible skin which allows water striders to walk on water.

Polarity is also related to solubility. Polar substances can dissolve other polar substances. Non-polar substances dissolve other non-polar substances. Polar substances and non-polar substances, however, do not mix. Dirt sticks to clothes and skin because it is combined with a thin layer of oil. Because water is polar and oil is non-polar , washing clothes in water alone does not remove all the dirt. This is why soap is used to clean clothes.

While one end of a soap molecule dissolves in water, the other dissolves in oil. This special dual ability of soap permits it to break up dirt so it can be removed easily. The polar end of the soap molecule dissolves in the water while the non-polar end dissolves in the oil. In this way, the oil is broken into droplets, surrounded by soap molecules, and dispersed. The droplets of oil do not merge together because the polar ends of the soap molecules have similar charges and repel each other. Because soap does not work very well in hard water, phosphates are often added to laundry detergents. The addition of phosphates to lakes can initiate the process of eutrophication.

Phosphates and nitrates are nutrients that algae use for growth. When these nutrients are available in abundance, algae may undergo explosive growth: an algae bloom. Eventually the bloom will die off and sink. Bacteria will then break down the dead plant material. These bacteria use up most of the oxygen dissolved in the water, leaving fish and other animals that live near the lake bottom to suffocate. This process, called eutrophication, is set in motion when excessive amounts of phosphates and nitrates enter the natural ecosystem. Some sources of these dissolved nutrients include raw sewage, fertilizer run off, detergents, and animal wastes.

When the algae bloom dies off, it will sink to the bottom of the lake because it is more dense than water. In the same way cold water and salty water tend to sink to the bottom because of their density. This is a major cause of deep ocean currents. When ice freezes near the poles, the salt concentrates in the liquid water of the ocean. The remaining water becomes more salty and therefore more dense. The dense, salty water sinks deep into the ocean and creates a current. The density of water increases with depth. Some animals change their depth by changing their density. Recall that things that are more dense than their surroundings sink while those that are less dense than their surrounding float. Most fish have a swim bladder, a special sac that is filled with gases from their blood. When the fish's swim bladder is full, it is less dense than the surrounding water and the fish will rise towards the surface.

Another property of water that affects lakes is the unique changes in density during phase changes. The density of most substances increases when a liquid becomes a solid. This is not so for water: Solid water is actually less dense than liquid water. It is for this reason that ice floats. Can you imagine a world where ice sank? Lakes would freeze from the bottom up, killing many fish. Frozen water in the polar regions would sink and change the ocean levels. The fact that ice floats is essential for the survival of many aquatic ecosystems and ultimately life on Earth

Besides the changes in density, there are other ways in which the phase changes of water have significant impacts. When water is trapped in small cracks in rocks, it will expand as it freezes and break up the rock causing weathering. The transpiration of water from a good-sized tree can move 1800 liters of water out of the ground in a single day. Sublimation, the phase change between solid and gas, is responsible for the formation of frost.

As you can see, water has many special properties that make its role in nature unique. One of water's special characteristics is the "stickiness" between water molecules. This qualities helps water to move through plant fibers. The cause of this "stickiness" also makes water an excellent solvent. In fact, water is considered the "universal solvent", able to dissolve a wide variety of substances. Even so, detergents are used to enhance water's ability to dissolve dirt. Phosphate, compounds that are added to detergents, can have a serious impact on lakes when they increase the growth rate of algae. Another way that lakes are affected by one of water's strange characteristics is how water freezes. Contrary to other substances, water is less dense in its solid form than in its liquid form, hence a solid that floats! Water is the only substance that occurs naturally in all three states. The characteristics examined in the paragraphs above are: capillary attraction, surface tension, solubility, density, and phase changes.

Name:

Class Period: 1 2 3 4 5 6 7 8

Water Reading Seminar

Spades- Surface Tension,

1. Explain polarity.
   
2. How is polarity related to surface tension ?
3. What does soap do to the surface tension of water?
4. What is the difference between adhesion and cohesion?

Diamonds - Capillary Attraction

1. How is polarity related to capillary attraction?
2. Give two examples of places where water moves upward by capillary attraction in nature.
3. Using your understanding of capillary attraction, explain how synthetic fabrics like Gore-tex work.
4. Why does water rise higher in thinner capillary tubes?

Clubs - Solubility and Phase Changes

1. How does polarity affect solubility?
   
2. Give examples of nutrients that are dissolved in lakes, rivers, and the ocean.
   
3. Describe a soap molecule's ability to dissolve water and oil.
   
4. Describe the phase changes that occur in the water cycle
   
5. How does freezing water contribute to the weathering of rocks?

Hearts - Density

1. Define density.
2. How does density affect ocean currents?
3. How does a fish's swim bladder affect its ability to change depths?
4. Why does ice float?
5. In which phase is water the most dense? the least dense?

PART II - Cooperative Questions. Meet with the other people in your group, those who have the same number playing card. Each person has completed a different set of questions, the ones that correspond to their Water Project topic. Present your set of answers and fill in the information as others present their specialty subject area..

PART III - Group Questions. Complete these questions as a group.

1. Explain how detergents are related to eutrophication.
   
2. How is polarity related to surface tension, capillary attraction, and solubility?
   
3. Describe the relationship between density and phase changes in water.

PART IV - Concept Map. Working as a group, build a concept map using the ten words amd phrases below and at least three of your own words. Place each word in a box and organize the boxes into a logical arrangement. Use a different color to label the lines that connect the boxes.

Required List: water, polarity, surface tension, capillary attraction, solubility, density, three phases, universal solvent, cohesion, adhesion.

Related Resources

Conte, David; Thompson, Donald; and Moses, Laurence. Earth Science: A Holistic Approach, Wm. C. Brown Publishers, Debuque, IA: 1994.

Deseret Newspaper in Education, Utah Geogrphic Alliance, Utah State Univeristy's College of Natural Resources. "Water Matters in Utah" (insert), November 9, 1993.

DiSpezio, Michael; Linner-Luebe, Marilyn; Lisouski, Marilyn, et al., Science Insights: Exploring Earth and Space, Addison-Wesley, Menlo Park, CA: 1996.

Hill, John. Chemistry for Changing Times, 6th edition, Macmillan Publishing Co., New York: 1988.

Keeton, William and Gould, James. Biological Science, 4th edition, W. W. Norton, New York: 1986.

Liem, Tik. Invitations to Science Inquiry, 2nd edition, Science Inquiry Enterprises, Chino Hills, CA: 1987.