Name Date Period Molecular Nature of Water

Transcription

1 Name Date Period Molecular Nature of Water Purpose: To determine how water molecules react using molecular models and Lab demos. Materials: I cup of 12 water molecules (red & white), 1 Na (blue), 1 Cl (green), ethane molecule String Capillary tubing Beaker Wax paper, paper towel, copy paper, penny, Ice Rubbing alcohol Pipette Test tube of water and oil 2 thermometers Experiment Take out ONE 3D Water molecules from your cup. (In reality water molecules can t be seen with the naked eye or with the most powerful microscope) 2. Draw and label the parts of the water molecule. Does this molecule have a charge? If so, how would you represent the charges? 3. What does each color of the molecule represent? Actually these colors are standard among chemists. 4. What is the chemical formula for water? 5. What does the 2 between the hydrogen and oxygen represent? 6. Predict what would happen if TWO water molecules bump into one another? 7. Take out the second water molecule and see what happens when they get close to each other. Explain what happened? 8. Draw what you see in the space below. 9. What other common item reacts the same way as your water molecule? What is the adjective used to describe this characteristic?

2 Experiment - 2 Obtain an ethane molecule. Ethane is a short hydrocarbon that is a colorless, odorless gas that can be used as a fuel, a freezing agent, and in making other chemicals. (Draw your molecule in the space below) 1. What do the different colors on the ethane molecule represent? 2. What is the chemical formula of ethane? 3. What is the intramolecular bond (within the molecule) that holds the hydrogen and carbon atoms within an ethane molecule? 4. Is an ethane molecule a polar covalent molecule, or a nonpolar covalent molecule? Why? 5. Will ethane form a hydrogen bond with water? Why or why not? 6. Will two ethane molecules form bonds with each other? Why or why not? 7. Observe the test tube containing the oil and water. Place your thumb over the test and gently shake it. Explain what you see now and a little later once the contents have settled. Experiment- 3 Tie a string loosely around ONE 3D Water Molecule (3DWM). Hold the string in one hand and another 3D Water Molecule in your other. Slowly bring the second 3DWM toward the one on the string. You should see the hanging molecule move toward the molecule in your hand. 1. This attraction is between two like molecules is called 2. How many water molecules can you string on a chain before the chain breaks? 3. A water molecule can attract other polar/ionic molecules. The attraction is called Experiment - 4 Fill the 250 ml beaker halfway with water. Immerse the capillary tube provided. Draw what you observed in the space below:

3 1. Explain what happened in terms of the water molecule. Experiment- 5 Place 10 drops of water on each of the base materials listed above. Draw what you see in the spaces below Wax paper Paper towel Copy paper Penny 1. Why does water bead up on some substances, and not bead up on others? 2. What is the term that explains what is happening here? 3. Can you explain how the water strider can walk on water? 4. What would happen if the water strider tried to walk on an oily surface? Experiment- 6 Different phases of water: Ice, Liquid and Vapor. 1. Take an ice cube from the ice bucket on the teacher s table and drop it in the beaker of water. What do you observe? 2. Construct an ice cube using the information below: Scientists have described 12 different structures of ice, many of which can be constructed with the 3DWM kit. To construct ICE 1h, hexagonal ice, follow these directions:

4 a. Hold one molecule horizontally in front of you (H atoms pointing to the sides) b. Add two vertical molecules to the two H atoms (H atoms pointing up and down) c. Add horizontal molecule to the lower H on each molecule added in step #2. d. Add one vertical molecule to connect the H atoms from the molecules added in step #3 e. Create a second hexagonal ring following steps #1-4. f. Orient the two hexagonal rings the same way- then rotate one ring 180 degrees. g. Place on hexagonal ring on top of the other. Do not flip one ring over- the H on both rings should point the same direction? Now set this aside as you do #5 below 3. Use this model and the observations from #1 to explain what is happening to the ice in water. Experiment- 6 General information: 1. Evaporation is the transformation from a liquid to a gas. This occurs when a liquid absorbs enough heat, increasing the movement of the molecules, to cause the intermolecular forces between molecules to break the surface tension. 2. Condensation is the transformation from a gas to a liquid. This occurs when a gas is cooled enough that the molecules slow down to form stronger intermolecular forces with each other. 3. What is this intermolecular force that needs to break and make when water changes state? 4. Procedure- (pick up the bottle of rubbing alcohol from the teachers table) Place a drop of water and a drop of rubbing alcohol 4cm apart on your forearm (try toplace this in an area on your forearm where there is no hair) Start timer Stop the timer when one of the liquids have completely evaporated Return the rubbing alcohol to the teachers table. 5. Which liquid evaporated first? 6. How did your skin feel as it evaporated? 7. Explain why? Experiment- 7 Obtain your Na and your Cl from your 3DWM kit. Remember Na is a metal and Cl is a nonmetal. 1. What kind of bond forms between these types of elements? 2. What is the chemical formula for this compound? 3. What s another name for this compound? 4. Let s demonstrate what happens when you put salt in water: a. Place a small scoop of salt in the beaker of water. Let it sit while you do the following. b. Place 12 3DWM s in your tub to demonstrate liquid water (refer to Experiment- 5) c. Place the sodium chloride in the center of the tub with the water surrounding it. d. Gently shake the tray.

5 5. What happened to the salt in the beaker? 6. What happened to the salt in your model? 7. Can you explain what happens to the salt when you put it in water? 8. Add more salt in the beaker? What happens when you add too much salt to water? Why does this happen? 9. What is this called? 10. What happens to the beaker of salty water (example- ocean water) when it is heated to boiling? Experiment There are two thermometers on the teacher s table. They are identical is every way except that one has a wet paper towel wrapped around its bulb and the other has a dry paper towel. Record the temperature of each: Wet, Dry. 2. Is there a difference in the temperature of each? 3. Using what you have learned in this lab, can you explain why? Conclusion: Please count all the model pieces to make sure that you have as many as you started out with. Empty the beaker with ice and water, salt and water, squeeze out all water from the pipettes, place all paper in trash. Place the cup of models in the tub along with the cleaned equipment and return to the cart. Reflection: Water is the essence of Life? What are the properties that water that make it indispensable for life on earth. List them and give examples for each. Use the other side.