Properties of Water Links updated 9-9-2014 Table of Contents Unit 1
Properties of Water Lab Date (unique to you) Page (unique to you) General Directions Read information about the properties of water and carry out the experiments using the materials at your lab station. Write the Experimental Question as the title for this lab in your lab notebook- not in the table of contents.
Write the names of your lab partners at the Experimental Question: What are the special properties of water? Partners Write the first and last names of your lab partners in your lab notebook. Objectives
Copy the objectives for this lab into your lab notebook: Objectives 1. Describe the structure of water. 2. Explain the properties of water important to supporting life on Earth. Write the vocabulary words and definitions in your lab notebook. Use the links to get information. Do the activities to strengthen your understanding of each concept.
Answer all numbered questions in red in your lab notebook. You do not have to write the question; although, your answer should be in a complete sentence. Make sure you label I. The Structure of Water Write this heading in your lab notebook . Answer all of the questions in RED in your lab notebook. Vocabulary
Define these words as you learn about the structure of water. Covalent bond Polar covalent bond Hydrogen bond Structure of Water () ()
O H (+) H (+) This is what a water molecule looks like. It is made of two hydrogen atoms connected by a covalent bond to one oxygen atom. (Note the shape!)
Covalent Bonds in Water () () The Hydrogen and Oxygen in water are bonded covalently. O Review Covalent bonds here
H (+) H (+) 1. _______(#) electrons are shared to form a covalent bond. 2. Why does oxygen form 2
bonds and hydrogen form one bond? ACTIVITY Build a water molecule using the molecular model pieces in the box. (blue is O and white is H) . 3. Draw a picture of water. 4. Write the chemical formula of water.
Water is Polar () () H and O atoms do not share the electrons evenly. 5. Which atom is larger? O or H? O H
(+) The oxygen in water has more protons, so the electrons tend to hang out at the oxygen end of water, making that end of the molecule slightly negative. H (+) This results in the two hydrogen atoms
becoming slightly positive. Add the + and charges to your picture of water. Structure of Water () () The uneven charge/sharing of electrons makes water POLAR. O
H (+) Take a closer look at polarity by watching the Ted Ed Video #1Polarity in my share drive. H (+) Polarity contributes to
emergent properties of water Batteries have + and pole! Earth has a north and south pole! 6.What is polarity? 7.Why is water considered polar?
Hydrogen Bonds The H+ on one water molecule is attracted to the O- of another water. () Hydrogen bond (+) H
(+) O () () (+) H (+ )
() This weak bond is called a hydrogen bond. Each water molecule can hydrogen bonds with 4 other water molecules. A single hydrogen bond is weaker than a single covalent bond. However, groups of hydrogen bonds are very strong. Hydrogen bonds are responsible
for the stickiness of water molecules Click through this animation to learn about water structure and hydrogen bonding. 8. Why do hydrogen bonds form between water molecules? 9. Draw 4 water molecules connected by hydrogen bonds. (Hydrogen bonds are drawn as dotted lines).
2. Water is the Universal Solvent Write this heading in your lab notebook Answer questions for this section under that heading! Vocabulary Define these terms as you learn about water and solutions. Solution Solvent
Solute Hydrophobic Hydrophilic Water is the universal solvent Solution = liquid consisting of uniform mixture of two or more substances Two parts of a solution: Solvent = liquid (dissolving agent) Solute = substance dissolved EXAMPLE:
Water = solvent; Koolaid powder/sugar = solutes; Kool-aid = solution Remember the rule to make a solution: like dissolves like Substances dissolve other substances that are similar/like it. Because water is polar, it will dissolve ions and other polar substances Hydrophilic = Water Lover
See a Solution up close! Non polar molecules are hydrophobic Oil is an example of a nonpolar molecule. It does not form hydrogen bonds. Like dissolves like; therefore, oil (nonpolar) does not mix with water (polar). Nonpolar molecules are hydrophobic (afraid of water)
because they do not mix with water. ** Click to the Solution part of this animation (about halfway through) 10. Briefly explain what a solution is, as well as its parts. 11. You make hot cocoa in the morning by adding a cocoa mix to a cup of hot water. Which is the solution, solute and solvent in this scenario? 12. Why are oil and water NOT able to mix?
ACTIVITY 1 Using the pipettes provided, add 2ml of water to a test tube. Gently add 2 ml of cooking oil to the same tube by tilting the test tube of water slightly and letting the oil run slowly down the inside of the test tube. 13. Describe what happened in your lab notebook. Include the terms hydrophilic and hydrophobic
ACTIVITY 2 Use a different test tube. Add 2ml of oil to the test tube. Gently add 2 ml of water to the same tube by tilting the test tube of oil slightly and letting the water run slowly down the inside of the test tube. 14. Describe what happened. Include the terms polar and non polar in your answer.
ACTIVITY 3 Add a few drops of food coloring to each test tube. Place your finger over the test tube and gently shake to mix the oil and water. 15. What happens to the food coloring in each test tube? Does it mix into the oil? Into the water? 16. Is the food coloring polar or non polar? Is it hydrophilic or hydrophobic
3. Water is Cohesive and Adhesive Write this heading in your lab notebook. Answer questions for this section under that heading. Vocabulary Define these terms as you learn how hydrogen bonds influence the behavior of water.
Cohesion Surface tension Adhesion COHESION Hydrogen bonding between water molecules causes them to stick together. Cohesion between water molecules produces SURFACE TENSION. The stickiness of water makes it seem as if it has an invisible skin on the surface.
Surface tension allows this water strider to walk across the surface of a pond. ***Watch the video called #2 - Surface tension & cohesion from the ISS found in my share drive. And forms drops on a blade of grass
ACTIVITY Use the pipet to gently drop water onto the surface of a penny until a clear bubble has formed on top but it is NOT overflowing. 17. How many drops could you put onto your penny? * Fill a beaker half full of water. Try to float a paper clip on the surface. 18. Can you can float a paper clip on the water surface of your penny?
19. What property of water allows you to do this? The Trick to the Paper Clip Place a paper clip under the first one. Then lower it into the water. The first should sink in. The second will not break the Hydrogen bonds and will float on top of the surface.
ACTIVITY Dry off your penny. With your finger, spread one small drop of detergent on the surface of the dry penny. Fill the top of a penny with water until a clear bubble has formed on top but it is NOT overflowing. 20. Describe the effect of the detergent. Did the detergent make a difference? Did the penny hold more, less or the same amount of water?
ADHESIO N Polarity also causes water molecules to stick to other substances. Adhesion makes water cling to the sides of a glass cylinder. 21. List 3 examples you have seen of water sticking to other objects. ** Watch the #3Cohesion and Adhesion video on my share drive to observe these properties
aboard the ISS. ACTIVITY What shape will a drop of of water form on: (a) a piece of wax paper (nonpolar) (b) a glass slide (polar) Perform the experiment. Place several drops of water on the glass slide and several drops on the wax paper. 22. Draw and label the results on wax paper and glass. Explain the differences in drop shape in terms of
adhesion - that is, the formation (or absence) of hydrogen bonds between water and another substance. CAPILLARY ACTION Water moves through a narrow passage in a process called capillary action. Capillary action describes how the water molecules move against gravity when
placed in a narrow passage. Capillary Action Water is pulled to the top of redwood trees as it evaporates from leaves at the top of the tree. ** Watch #4Capillary Action in my share drive and #5- Cap. Action
ACTIVITY Use a beaker and a strip of paper towel (not folded over) that is just long enough to hang over the side of the beaker (inside) and reach almost to the bottom. Place a single small drop of ink from a vis-avis pen on the paper, about one inch from the bottom, and let it dry completely. (continued on next slide) ACTIVITY Put a small amount of water into the beaker and
place the strip of paper in the beaker so that the bottom end of the paper is in water and the drop of ink is just above the surface of the water. Fold the paper over the top of the test tube. Use a paper clip to hold it to the edge. Note the starting time in your notebook. 23. Predict how long it will take for the water to reach the top of the paper. Watch and note the time at 5 minute intervals. When the water climbs to the top of the paper, remove the paper from the water, and let it dry. (NOTE: go on to other experiments while you are
waiting!) ACTIVITY 24. Record how long it took for the water to reach the top. Describe what happened to the ink as the water travelled up the paper. 25. Use the terms cohesion and adhesion to explain capillary action. 4. Specific Heat Capacity
Write this heading in your lab notebook. Answer questions for this section under that heading. Vocabulary 26. Define this term as you learn about the high specific heat of water. Specific heat Specific Heat - Definition
The specific heat of water is the amount of heat (energy) needed to raise the temperature a certain amount. Water has a high specific heat capacity because hydrogen bonding increases interaction between water molecules. It takes a lot of energy to raise 1 gram of water by 1 degree Celsius because you must break hydrogen bonds between water molecules. HIGH SPECIFIC HEAT
So Liquid water can absorb large amounts of heat with small changes in temperature So Water heats up more slowly and retains heat longer than surroundings Why is this important? This is important for many reasons: For instance it helps
us maintain a constant body temperature, even when the temperature around us changes HIGH HEAT OF VAPORIZATION Vaporization (evaporation) is the change from liquid to gas. Molecules of liquid escape and enter air.
It takes a lot of energy to convert liquid water into vapor because hydrogen bonds hold the water molecules together. ACTIVITY Click this link and do the activity: Changing Matter Just click Increase temperature until new text appears. 27. Describe what happens to the water molecules as you increase the heat.
What property of water makes it able to absorb a great deal of energy before it changes from solid to liquid to gas? (Hint: explain what has to break to release water molecules from each other) Note: Heat is total energy (all the movements of all the particles in a substance) Temperature is a measure of energy (average energy of movement in a substance) . As you add heat, the temperature will rise.
Evaporation As water evaporates, it removes heat and produces cooling (evaporative cooling). Many organisms take advantage of the fact that water absorbs a great deal of energy going from liquid to vapor state to maintain body temperature. Sweating (people) and panting (dogs) are two ways to prevent overheating. Activity
Demonstrate evaporative cooling by placing a thermometer in room temperature water. Remove the thermometer and note the change in temperature as the water on the thermometer evaporates. 28. Record the two temperatures. How would this property of water keep you cool on a hot day? Why does sweating cool your body down? Ice Is Less Dense Than Water
Water expands when it freezes (one of few substances that does this) SO . . . ICE IS LESS DENSE THAN LIQUID WATER Hydrogen bonds keep molecules at arms length when freezing so ice floats Density of Ice This is important to insulate bodies of water. Lakes freeze from top down; allowing living things to survive in winter when the lake freezes.
Water Alcohol This blue ice cube floats in water because ice is less dense than liquid water. The blue ice cube sinks in alcohol because ice has a greater density than
alcohol. Watch #6- Ice in my share drive to learn why ice floats. Ice Density 30. Explain what would happen to fish and frogs during the winter if ice was more dense than water. Clean Up!
CLEAN UP EVERYTHING ON YOUR STATION. DO NOT DUMP OUT THE ROOM TEMP WATER. WIPE UP ALL SPILLS. CLEAN OUT TEST TUBES AND BEAKERS. Detentions will be issued for groups
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