Properties of Water Lab

Properties of Water Lab Explain why the special properties of water make it essential for life. Materials: Every station: A reading about that particular property of water Station 1: Two water molecule building sets Station 2: two vials with caps containing colored salt and water, two vials with caps containing colored salt and vegetable oil Station 3: Two Dixie cups – one flled with water, the other with rubbing alcohol, two pennies, pipettes and paper towels Station 4: A beaker flled with ice, a cup half-way full of water and a cup of vegetable oil with a polymer ball inside Station 5: 6 graduated cylinders flled with 20mL of water, paper towels cut into 1in, 2in, and 3in strips Station 6: 4 bowls – 2 flled with water, the other two filled with soapy water, paper clips, plastic forks, paper towels Station 7: Q-tips, one cup with rubbing alcohol, one cup with water, a timer/stopwatch (5 min): Explain rotation lab We are going to go through 7 stations to explore each individual characteristic of water that makes it different to other molecules. You will start at the station that is at your table. You will be working with your shoulder partners. The frst thing you do at your station is read the yellow sheet and answer the reading questions on your handout. Do not start any experiments until you have completed your reading and reading questions. Next, you will move on to the experiment which includes very specifc instructions on your yellow sheet. There are also supplemental tips at certain stations to make sure you are completing the experiment successfully and not ruining any variables for the next group who performs the same experiment”: GIVE AN EXAMPLE. “There are also questions that you will need to answer when completing the experiment. These questions should be flled as you do the experiment or after completing the experiment. Finally, you will clean up your station and return it as you found it. Put any used paper towels in the trash bin. When you fnish the station, you have analytical questions to complete. If you have time, do these after each station. If you do not complete them now, you may fnish them for homework. For now, focus mainly on reading the description, answering the reading questions, completing the experiment and answering the experiment questions and then cleaning your stations before you move to the next one. The analytical questions can be completed at a later time if necessary.” Have each shoulder partner explain to the other the instructions of the lab. (56 min): Station rotations Students move through the stations and complete the instructions. There will be 8 minutes for each station, 7 station rotations total. (4 min): Clean up and recap Students are required to clean up their lab area and finish any questions they missed. The students will throw away any used paper towels in the trash bin. Guiding Critical Thinking: Students are asked to think critically about the properties of water and how they apply to the maintenance and improvements of life. Instead of simply giving the students the information about water, they are required to work in groups to discover the properties of water with hands-on manipulatives that accompany a short reading. Assessment: Students will turn in their water rotation lab the next day, after completing the analysis questions. Formative assessment comes from completing individual sections of the lab before moving to the next station. STATION 1 – Water is a polar molecule and has a very unique structure. A water molecule, because of its shape, is a polar molecule. That is, it has one side that is positively charged and one side that is negatively charged. The molecule is made up of two hydrogen atoms and one oxygen atom. The bonds between the atoms are called covalent bonds, because the atoms share electrons. The hydrogen atoms have one electron each. Because they share those electrons with the oxygen atom, the electrons tend to stay close to the oxygen atom and the outside of the hydrogen atom tends to be positively charged. The oxygen atom has eight electrons. Most of those tend to stay away from the hydrogen atoms, and cause the outside of the oxygen atom to have a negative charge. When two water molecules get close together, the polar forces work to draw the molecules together. The oxygen atom of one water molecule will bond with hydrogen atoms of other water molecules. These bonds are called hydrogen bonds. Hydrogen bonds are not as strong as covalent bonds, but they are strong enough to bind water molecules together and give water its unique characteristics. (An analogy concerning the bonds is that the covalent bonds are like a strong glue bond while the hydrogen bonds are like the bond between two toy magnets). Activity: Read all instructions before conducting the activity 1. Observe the model of a molecule of water and complete the questions that pertain to the model on your student worksheet. STATION 2 – Water is the universal solvent. Solutions and suspensions: Water is not always pure – it is often found as part of a mixture. A mixture is a material composed of two or more elements or compounds that are physically mixed together but not chemically combined. Salt and pepper stirred together constitute a mixture. So do sugar and sand. Earth’s atmosphere is a mixture of gases. Living things are in part composed of mixtures involving water. Two types of mixtures that can be made with water are solutions and suspension. If a crystal of table salt is placed in a glass of warm water, sodium and chloride ions on the surface of the crystal are attracted to the polar molecules. Ions break away from the crystal and are surrounded by water molecules. The ions gradually become dispersed in the water, forming a type of mixture called a solution. All the components of a solution are evenly distributed throughout the solution. In a saltwater solution, table salt is the solute, the substance that is dissolved. Water is the solvent – the substance in which the solute dissolves. Water’s polarity gives it the ability to dissolve both ionic compounds and other polar molecules, such as sugar. Without exaggeration, water is the greatest solvent on Earth. Activity: Read all instructions before conducting the activity 1. Shake and observe the test tube that has oil plus salt. 2. Shake and observe the test tube that has water plus salt. 3. Answer the questions on your student worksheet. STATION 3 – Water has the properties of adhesion and cohesion. A single water molecule may be involved in as many as four hydrogen bonds at the same time. The ability of water to form multiple hydrogen bonds is responsible for many of water’s properties. Cohesion is an attraction between molecules of the same substance. Because of hydrogen bonding, water is extremely cohesive. Water’s cohesion causes molecules on the surface of water to be drawn inward, which is why drops of water form beads on a smooth surface. Cohesion also explains why some insects and spiders can walk on a pond’s surface. Adhesion is an attraction between molecules of different substances. Have you ever been told to read the volume in a graduated cylinder at eye level? The surface of the water in the graduated cylinder dips slightly in the center because the adhesion between water molecules and glass molecules is stronger than cohesion between water molecules. Adhesion between water and glass also causes water to rise in a narrow tube against the force of gravity. This effect is called capillary action. Capillary action is one of the forces that draw water out of the roots of a plant and up into its stems and leaves. Cohesion holds the column of water together as it rises. Activity: Read all instructions before conducting the activity 1. Obtain a clean penny. 2. Using the appropriate pipette, count how many drops of water can fit on a penny before spilling over. Record in your data table. 3. Make a drawing of the penny + water on your student sheet (before it spilled over – you may have to repeat the experiment). 4. Clean off the penny. 5. Using the appropriate pipette, count how many drops of rubbing alcohol can fit on a penny before spilling over. Record in your data table. 6. Make a drawing of the penny + rubbing alcohol on your student sheet (before it spilled over – you may have to repeat the experiment). 7. Clean off the penny. STATION 4 – Water is less dense as a solid than a liquid. Water is one of the few substances that are less dense as a solid than as a liquid. In other words, ice (water’s solid form) has the ability to float on liquid water. While other materials contract and become more dense when they solidify, water expands into an evenly distributed crystalline structure. This is due to the hydrogen bonds inside water molecules. The hydrogen bonds keep the molecules at “arms-length,” far enough apart to make ice just dense enough to float on the liquid surface. When ice absorbs enough heat for its temperature to rise above 0°C, hydrogen bonds between molecules are disrupted and changed from “arms-length” to shorter, more easily breakable bond formations. The ability of ice to float due to its lower density is an important factor in making the environment suitable for life. If ice sank, then eventually all ponds, lakes and even oceans would freeze solid, making life as we know it impossible on Earth. During summer, only the upper few inches of the ocean would thaw. Instead, when a deep body of water cools, the floating ice insulates the liquid water below, preventing it from freezing and allowing life to exist below the frozen surface. Besides insulating the water below, ice also provides a solid habitat for animals such as polar bears and seals. Activity: Read all instructions before conducting the activity 1. Observe the cup with vegetable oil and the polymer ball. 2. Observe the cup with the water and the ice. STATION 5 – Water is important for capillary action. Water molecules are attracted to one another by a force called cohesion. Because of cohesion, water molecules have a tendency to form hydrogen bonds with each other. Water molecules can also form hydrogen bonds with other substances. This results in a force called adhesion, which is the attraction between unlike molecules. The tendency of water to rise in a thin tube is called capillary action. Water is attracted to the walls of the tube, and the water molecules are attracted to each other. The thinner the tube, the higher the water will rise inside it. Plants use capillary action in their xylem to suck water from the ground against the force of gravity. Activity: Read all instructions before conducting the activity 1. Cut a paper towel into three different widths: 1cm, 2cm, 3cm. Keep the length the same for all the paper towels, and make sure there are no folds in the towel. 2. Fill three graduated cylinders with 20 mL of water. 3. Place the paper towels in separate graduated cylinders just until the towel touches the water, and fold it over the edge of the graduated cylinder. 4. Time the movement of water up the paper towel for one minute. 5. Take out the strips of paper and measure (in centimeters) how far the water moved up each towel. STATION 6 – Water has a strong surface tension. The cohesive property of water gives it a high surface tension. Surface tension describes the “stickiness” of water molecules on the surface of water. The attraction of the water molecules creates a strong flm on the water’s surface. Surface tension allows water to hold up materials heavier and denser than itself. For example, the high surface tension of water enables a paper clip to float on the surface of water, and also allows some insects to walk on the surface of water. Activity: Read all instructions before conducting the activity 1. Take a paperclip, and using the fork, place it gently on the surface of the water. 2. Continue adding paper clips and record the maximum number of paperclips you and your partner were able to add without any of the clips falling to the bottom. 3. Repeat the same procedure above, but instead use soapy water. 4. Answer the questions on your student worksheet. STATION 7 – Water has a high heat of vaporization The heat of vaporization is the quantity of heat a liquid must absorb for 1 gram to be converted from a liquid to a gas. It can take twice as long for water to evaporate than liquids such as ammonia. This property is the result of hydrogen bonds, which must be broken in order to turn water into a gas. As a liquid evaporates, the surface of the liquid that remains behind cools down. This evaporative cooling occurs because the “hottest” molecules are the most likely to leave as a gas. Evaporative cooling of water contributes to the stable temperature of lakes and rivers and also provides a mechanism that prevents terrestrial organisms from overheating. For example, evaporation of sweat from human skin dissipates body heat and helps prevent overheating on a hot day when excess heat is generated by lots of activity. High humidity on a hot day makes one feel uncomfortable because the high amount of water vapor in the air prevents the evaporation of sweat from the body. Activity: Read all instructions before conducting the activity 1. At your station you will fnd two containers with a cotton swab soaking in a liquid. 2. Have your partner swab a small area on the inside of your l e f arm with the cotton swab soaked in w a ter . 3. Time how long it takes for the water to evaporate. 4. Have your partner swab a small area on the inside of your r ig h t arm with the cotton swab soaked in r ubbi n g a lc ohol . 5. Time how long it takes for the alcohol to evaporate. 6. Repeat the above procedures on the other partner. Copy and cut the tips out to place at the appropriate lab station. Tips: Keep the pipettes in their designated solutions. Do NOT use the pipette for anything other than its original use. Mixing solutions will cause inaccurate results and ruin the station. Dry the penny after each use with provided paper towels. Dispose of paper towels in Trash bin provided. Tips: Only put the ice in the water cup, DO NOT put ice in the oil cup Keep the table and materials dry with paper towels Dispose of paper towels in Trash bin provided Tips: Use the strips provided, one in each cylinder Place the strip in the cylinder so that only the base of the strip is touching the very top of the water Throw away the strips in the Trash bin provided DO NOT put used strips in with unused strips Tips: Make sure forks and paper clips are completely dry before testing the experiment Make sure the fork is completely fat and level when entering the water Make sure the fork is completely vertical when exiting the water Dry forks and paper clips after every use Put used paper towels in Trash bin provided Name Date Per Properties of Water Write everything you know about water this box. STATI O N 1 Wa – t er i s a po l ar mo l ec u le a nd h a s a very un i que s t r ucture. Answer the following questions from the reading provided. 1. What is a polar molecule? 2. Name the elements that make up water. 3. What charge does the hydrogen atoms have in a molecule of water? 4. What charge does the oxygen atom have in a molecule of water? 5. The other water molecules. atom of one water molecule will bond with atoms of 6. What are the bonds called between two hydrogen atoms? Answer the following questions afer completing the activity. 1. Draw one molecule of water and label the hydrogen and oxygen atom. La b el the positive (+) region of the molecule and the negative (-) region of the molecule. 2. Draw 5 molecules of water bonded together with hydrogen bonds. Label one hydrogen bond, oxygen atom, and hydrogen atom. Analysis Questions Explain why it is important for hydrogen bonds to be weak bonds instead of strong bonds. STATI O N 2 Wa – t er i s t h e u niv e rs a l s o lv e n t . Answer the following questions from the reading provided. 1. Define mixture. 2. What are the two types of mixtures? 3. Define solute. 4. Define solvent. 5. Why is water considered the greatest solvent on Earth? Answer the following questions afer completing the activity. 1. Describe the appearance of the test tube with oil and salt. (Use complete sentences and be detailed) 2. Describe the appearance of the test tube with water and salt. (Use complete sentences and be detailed) Analysis Questions Up to 60% of our body is made up of water. Describe the signifcance of water being a universal solvent in o u r bo d i e s . STATI O N 3 Wa – t er h as t h e pr o p e r t ies of adh e s i on a n d coh e s i on. Answer the following questions from the reading provided. 1. How many hydrogen bonds can a single water molecule have? 2. Defne cohesion. 3. Defne adhesion. Answer the following questions afer completing the activity. How many drops can fit on a penny? Water Rubbing Alcohol Number of Drops that Fit on a Penny What does the solution look like on the penny? Water Rubbing Alcohol 1. Explain why more water drops could fit on a penny when compared to rubbing alcohol. 2. What property of water allows the water to stick to the penny? 3. What property of water allows the water to form a dome-like structure on top of the penny? Analysis Questions Describe an example of cohesion and adhesion that you might observe during your daily life. STATI O N 4 Wa – t er i s le s s de n se as a so li d th a n a l i q u i d. Answer the following questions from the reading provided. 1. Why can solid ice float on liquid water? 2. When a lake freezes, how does the density of water prevent all of the living organisms in the lake from freezing as well? Answer the following questions afer completing the activity. 1. Describe why the polymer ball is at the bottom of the vegetable oil. 2. Describe why the ice floats on the water. Analysis Questions Imagine a world where ice was more dense than liquid water. What would this world be like? What would the consequences be for life in your local freshwater streams and lakes. STATI O N 5 Wa – t er i s imp o r t a n t for c a pi ll a r y action. Answer the following questions from the reading provided. 1. What two properties of water contribute to capillary action? 2. How does water move up the thin walls of a tube? Specifcally, what is it sticking to? Answer the following questions afer completing the activity. Distance the Water Moved (centimeters) 1cm Paper Towel 2cm Paper Towel 3cm Paper Towel Analysis Questions Explain why the vessels that transport water in trees must be very small in diameter. STATI O N 6 Wa – t er h as a s tr o ng sur f ace t en s i on. Answer the following questions from the reading provided. 1. How does water hold up materials that is heavier than itself? 2. What property of water gives it a high surface tension? Answer the following questions afer completing the activity. Plain Water Soapy Water Number of Paperclips that floated 1. What property of water allows the paper clips to be attracted to the plain water? 2. How did the soap affect the paper clip’s ability to float? Analysis Questions Explain why this property of water is essential for organisms like water bugs. STATI O N 7 Wa – t er h as a high h e a t of va p or i z a ti o n Answer the following questions from the reading provided. 1. Define heat of vaporization. 2. What causes water to have a high heat of vaporization? 3. What happens to the surface when water evaporates? Time (seconds) Water Rubbing Alcohol Analysis Questions 1. How does water’s high heat of vaporization help you feel cooler when you sweat? 2. Describe the importance of high heat of vaporization to ecosystems.