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Laboratory Title The Miracle Molecule

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					Laboratory Title: The Miracle Molecule Your Name: Yvonne Kelley
http://www.exploratorium.edu/ronh/bubbles/sticky_water.html http://www.biology.arizona.edu/biochemistry/tutorials/chemistry/page3.html http://witcombe.sbc.edu/water/chemistry.html Taken from PBS Zoom’s website: http://pbskids.org/zoom/activities/sci/floatingpaperclips.html

Concepts Addressed: The atomic structure of the water molecule and its chemical and physical properties. Lab Goals: Students will understand the unique properties of the water molecule including its structure, hydrogen bonding, and surface tension. Lab Objectives: Students will:  Make models of a water molecule using popcorn balls showing the polarity of the molecule  Simulate how hydrogen bonding works using the popcorn models  Explore the surface tension of water by floating paper clips on its surface Benchmark(s) Addressed:  4.1E.1 Identify properties, uses, and availability of Earth materials.  4.3S.1 Based on observations identify testable questions, design a scientific investigation, and collect and record data consistent with a planned scientific investigation.  4.3S.2 Summarize the results from a scientific investigation and use the results to respond to the question being tested.  4.4D.1 Identify a problem that can be addressed through engineering design using science principles.  5.2P.1 Describe how friction, gravity, and magnetic forces affect objects on or near Earth. Background Material: (Students will have already been introduced to what atoms are and the periodic table. Students will have also studied phases of matter before this activity. If phases of matter need to be introduced or reviewed, check out http://www.chem4kids.com/files/matter_intro.html and go to phases of matter to get background information. Types of chemical bonding and its mechanisms are also not addressed in this lesson plan. Further explorations of water chemistry could include lessons with acids/bases and/or testing water supplies as a cross-unit with ecology) The polarity of water: Water has a simple molecular structure. It is composed of one oxygen atom and two hydrogen atoms. Each hydrogen atom is covalently bonded to the oxygen via a shared pair of electrons. Oxygen also has two unshared pairs of electrons. Thus there are 4 pairs of electrons surrounding the oxygen atom, two pairs involved in covalent bonds with hydrogen, and two unshared pairs on the opposite side of the oxygen atom. Oxygen is an "electronegative" or electron "loving" atom compared with hydrogen.

Water is a "polar" molecule, meaning that there is an uneven distribution of electron density. Water has a partial negative charge (Delta-) near the oxygen atom due the unshared pairs of electrons, and partial positive charges (Delta-) near the hydrogen atoms. If you could see molecules of water and how they act, you would notice that each water molecule electrically attracts its neighbors. Hydrogen atoms have single electrons which tend to spend a lot of their time "inside" the water molecule, toward the oxygen atom, leaving their outsides naked, or positively charged. The oxygen atom has eight electrons, and often a majority of them are around on the side away from the hydrogen atoms, making this face of the atom negatively charged. Since opposite charges attract, it is no surprise that the hydrogen atoms of one water molecule like to point toward the oxygen atoms of other molecules. The extraordinary properties of water are due to these two hydrogen atoms, which are arranged on one side of the molecule and are attracted to the oxygen atoms of other nearby water molecules in a state known as "hydrogen bonding." (If the molecules of a liquid did not attract one another, then the constant thermal agitation of the molecules would cause the liquid to instantly boil or evaporate.) There are many unique properties of water that are due to these hydrogen bonds. For example, ice floats because hydrogen bonds hold water molecules further apart in a solid than in a liquid, where there is one less hydrogen bond per molecule. Of course in its liquid state, the molecules have too much energy to become locked into a fixed pattern. However, the numerous temporary "hydrogen bonds" between molecules make water an extraordinary sticky fluid. Surface Tension Of Water: Within the liquid state of water, every molecule is engaged in a tug of war with its neighbors on every side. For every "up" pull there is a "down" pull, and for every "left" pull there is a "right" pull, and so on, so that any given molecule feels no net force at all. At the surface things are different. There is no up pull for every down pull, since of course there is no liquid above the surface; thus the surface molecules tend to be pulled back into the liquid. It takes work to pull a molecule up to the surface. If the surface is stretched - as when you blow up a bubble - it becomes larger in area, and more molecules are dragged from within the liquid to become part of this increased area. This "stretchy skin" effect is called surface tension. Surface tension plays an important role in the way liquids behave. If you fill a glass with water, you will be able to add water above the rim of the glass because of surface tension. Other unique physical properties of water due to hydrogen bonding include a high heat of vaporization, high specific heat, and its ability to be a nearly universal solvent. Materials and Costs: List the equipment and non-consumable material and estimated cost of each Item.......................................................................................................................... Cost Plastic cocktail cups (25 pack) .................................................................................... 4.95 Estimated total, one-time, start-up cost: ...................................................................4.95 List the consumable supplies and estimated cost for presenting to a class of 30 students Item.......................................................................................................................... Cost Popcorn, plain & popped (Bulk) ................................................................................. 5.00 Light corn syrup ......................................................................................................... 3.59

Margarine ................................................................................................................... 3.99 Cold water ............................................................................................... free from tap Confectioner’s sugar .................................................................................................. 5.49 Marshmallows ............................................................................................................ 6.59 Food coloring ............................................................................................................. 4.99 Toothpicks ................................................................................................................... 2.49 Paper clips .................................................................................................................. 2.49 Paper towels ............................................................................................................... 2.49 Estimated total, one-time, start-up cost: ..................................................................37.12 Time: Preparation time: 3-4 hr. to purchase supplies and make popcorn balls. Use following recipe for popcorn balls. Add a different food coloring to each batch. One batch will make 20 large balls (Oxygen balls) or 40 small balls (Hydrogen balls). Adjust for classroom size. Popcorn Balls Ingredients: * 3/4 cup light corn syrup * 1/4 cup margarine * 2 teaspoons cold water * 2 5/8 cups confectioners' sugar * 1 cup marshmallows * 5 quarts plain popped popcorn Preparation: 1. In a saucepan over medium heat, combine the corn syrup, margarine, cold water, confectioners' sugar and marshmallows. (Add food coloring if desired) Heat and stir until the mixture comes to a boil. Carefully combine the hot mixture with the popcorn, coating each kernel. 2. Grease hands with vegetable shortening and quickly shape the coated popcorn into balls before it cools. Wrap with cellophane or plastic wrap and store at room temperature. * Other preparation items could include handouts of a periodic table, and background information for their reference. Ideally, try to have some books available in the classroom that students can reference when working on their water poster (see assessment) Instruction time: Approx. 30 minutes. Use power point to give chemistry information and as prompts for activities (see procedures for more information). Clean-up time: Approx. 5 minutes. Students can keep the popcorn balls. Have them return plastic cups for reuse.

Procedures:  Use power point to start lesson.  After going over the building blocks of a water molecule, have students build their own water molecules using popcorn balls. (These are made before class; see recipe in preparation section.)  Let students try to figure out how to construct the molecule for a few minutes before showing an example of how the molecule is constructed. (Have a model made beforehand to show students the correct construction of a water molecule.)  Explain that the toothpicks represent the bonds that are made between the hydrogen and the oxygen. The angle of the two hydrogen atoms bonded to the oxygen is 104.5o.  After everyone has their models made, introduce hydrogen bonding using the power point presentation.  After going over hydrogen bonding, instruct students to see if they can model how water molecules bond to each other.  Ask students how they think the water molecules bond together differently in its liquid state versus its solid state. (In its liquid state, water molecules move around more than in its solid state and the hydrogen bonds are temporary. In water's solid state, the bonds are fixed and create a lattice structure. This structure is what gives ice a lesser density than liquid water.)  After students have time simulating hydrogen bonding, continue power point presentation on surface tension.  Have students do the paper clip activity. (See last page of lesson plan for instructions on activity.)  Instruct students to write down their observations of both activities in their lab books. (If students do not have designated lab books, have them write down observations on a piece of paper.)  They will be using their observations to create a water molecule poster. (See assessment.)  Continue power point presentation to wrap up lesson and review concepts. Assessment (include all assessment materials):  Have students create a water molecule poster. Poster criteria includes a diagram of a water molecule, it’s chemical formula, the results from their surface tension experiment, an explanation of hydrogen bonding and how it affects water’s surface tension.  Additional materials need for this assessment assignment (if done in class rather than assigned as homework) would be construction paper, colored markers, colored pencils, scissors, & glue sticks  Quiz Question: 1. What allows the water molecule to have so many unique properties? Answer: hydrogen bonding

Floating Paper Clips
Materials Needed: * bowl of water * paper towels * paper clips

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Fast dips sink clips! Can you make a paper clip float?

Instructions: 1. Drop a paper clip in a cup of water. What happens? 2. Tear off a piece of paper towel that is slightly larger than the paper clip. 3. Place the piece of paper towel on top of the water. 4. Gently place another paper clip on the piece of paper towel. Wait a few seconds. Now what happens? Explanation: If you drop a paper clip in water, the paper clip sinks. But if you put the paper clip on a piece of paper towel, the paper towel sinks and the paper clip floats. This is because water particles are attracted to each other in all directions, making them "stick" together. However, because there are no water particles above them, the water particles at the surface "stick" only to particles next to and below them. This makes the surface act as if it had a thin "skin". This is called surface tension. The paper towel helps you to lower the paper clip onto the surface gently without breaking the surface tension. If you're very careful, you can float the paper clip on the water without using the paper towel. Now it's time for you to experiment. What happens if you add a drop of liquid soap to the water while the paper clip is floating? Or, what happens if you put the paper clip in another liquid, like vegetable oil or soda water?

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Taken from PBS Zoom’s website: http://pbskids.org/zoom/activities/sci/floatingpaperclips.html


				
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