Teacher Instructions

Transcription

1 The Challenge: Middle School Science Challenge Pilot: Providing Clean Water Teacher Instructions Build a desalination system to convert dirty saltwater into clean drinking water as efficiently as possible. About this Science Challenge: This challenge explores the importance of delivering health care and medicine everywhere it is needed, whether that is in our own community, in a remote part of a developing nation, or anywhere after a catastrophic disaster (like a major earthquake). Having access to clean water is a basic necessity for good health and a critical part of both preventative medicine and acute medical care. According to the United Nations Educational, Scientific, and Cultural Organization, nearly 800 million people do not have access to clean water, and, according to the World Health Organization, approximately 2.6 billion people do not have an improved toilet (a toilet that greatly reduces the chances of pathogens from human waste getting in to the local water ecosystem). This lack of safe drinking water and sanitary conditions causes the death of an estimated 1.6 million people every year, mostly in developing countries. Additionally, these unsafe conditions significantly impact the overall quality of life for hundreds of millions of people in developing countries. Common waterborne illnesses that are spread through the use of unclean water include: cholera, parasitic worms (e.g., Schistosomiasis and intestinal hookworms), trachoma (a bacterial disease that can cause blindness), and hepatitis A. Just as lack of clean drinking water can lead to diseases, the health of already ill patients can be further compromised by unclean water. Many medicines need to be taken with water, and if the water is unclean, each dose of medicine increases the risk of a new infection. Similarly, even basic first aid, like the washing of wounds, becomes risky without water free of microbes, parasites, and contaminants. One way that water can be purified (turned into clean water) is through evaporation. Specifically, when water is heated up enough, the water evaporates. Once water vapor cools, it forms condensation, which can be collected and consumed as clean drinking water. When discussing this challenge with students, teachers may want to review what evaporation and condensation are at this point. The high temperature required to turn the water into water vapor kills the majority of infectious agents. An advantage of this method of water purification as compared to purification by filtration or chemical treatment of the water is that as the water evaporates, it leaves behind contaminants. This means it can be used as a method of desalination (the conversion of saltwater to drinking water), too. Droughts and desertification are increasingly diminishing the world's access to fresh drinking water. As this occurs, readily available saltwater from the ocean is being looked at as a solution, but first, desalination is needed to convert it to fresh water. The key components of a simple desalination system are a container that holds the dirty water, a surface that the evaporated water can condense on, and a collection container that the condensate drips into and which holds this purified water. Created by Science Buddies for Genentech's Middle School Science Challenge Pilot

2 Design and Testing Notes for Teachers: Figure 1, below, shows three examples of different desalination systems. Systems #1 and #2 could be made for the Providing Clean Water challenge, and a variation of #3 could also be constructed using a funnel (instead of a glass tube with cooling water). There are also other possibilities that students may figure out. Figure 1. Examples of three different types of desalination systems; variations based on these could be made for the Providing Clean Water challenge. (System #3 is a chemistry distillation apparatus that uses glassware.) Systems #1 and #2 in Figure 1 use a large metal can as the container that holds the saltwater, and a smaller container to collect condensate (the condensation that is gathered together). System #1 is made using plastic wrap with a metal washer on it to form a low point on the plastic wrap as a surface for the water to condense on. The condensation collects at the low point on the plastic wrap, and drips into the collection container below. System #2 is made with a rectangular container (filled with ice cubes) that allows condensation to collect on an underside corner of the container, and then drip into the collection container below. System #2 is probably more efficient at making purified water than system #1 because it involves the use of ice cubes (to cool the water vapor quickly and create condensation), has a raised collection container (so the collected condensate remains cooler), and uses a rectangular container that may form a smoother path to the dripping condensate point (wrinkles can easily form in the plastic wrap in the system on the left). System #3 uses cooling water around a glass collection tube to cool the water vapor quickly and create condensation. Students could make a system similar to system #3 using a funnel instead of a tube. A few possible design flaws students may encounter and problem-solve are: Water vapor is escaping and lowering the efficiency of the system. Condensation is not effectively being channeled into a collection receptacle. Purified collected water is being re-vaporized into water vapor. In Science Buddies' testing, we were able to collect 26 ml of pure water (8 ppm salinity) in 20 minutes from a system based on system #2 in Figure 1, above, sitting on a 500 C hot plate with a starting volume of 500 ml of saltwater. More-efficient designs may be possible, but this water collection amount is just a ballpark for an Created by Science Buddies Genentech's Middle School Science Challenge Pilot Page 2

3 effective system. It is likely, given that this is the first time students are thinking about such a system, that the student systems will result in less water collected. Materials Needed per team (3-4 students) to build a desalination system (both day 1 and day 2): No. 10 tin can (approx. 105 oz size) Size 32 rubber band (fits snugly around the No. 10 tin can) 16 oz tin can Aluminum foil, 1 sheet measuring about 30 cm by 40 cm (12 inches x 16 inches) Plastic wrap, 1 sheet measuring about 30 cm x 40 cm (12 inches x 16 inches) 9 oz plastic, disposable cup 18 oz plastic, disposable cup Shipping tape Duct tape Scissors, for cutting the tape or possibly plastic cups Ruler (metric), for measuring how much tape they are using Metal washers (3) Square or rectangular plastic container (for use on the top of the system #2 in Figure 1, above). It should be between 10 cm-20 cm wide/deep and 4 cm-8 cm high. Wooden craft sticks (5-10) Small funnel (for use in a system similar to system #3 in Figure 1, above, in place of a cooling collection tube) Day 1 Worksheet (1 per student, for day 1 only) Project Cost Tracking Table (1 per team) Needed per team (3-4 students) to test a desalination system (day 2 only): Hot plate that can reach 500 C and has a surface that is at least 6 inches wide Oven mitts Safety goggles or glasses (1 pair per student) 2 oz mini plastic cup for measuring water purity Graduated plastic pipette, 3 ml Day 2 Worksheet (1 per student) Challenge Judging Rubric (1 per team) Reflection Worksheet (1 per student) Needed for the entire classroom to share (day 2 only): Ice cubes, should be stored in a cooler for the entire classroom to use Graduated measuring cup, for distributing discrete quantities of ice cubes to each team "Dirty" water 1 L per team. For preparing the "dirty" water, you will need: o 12 L bucket to make the solution in o A 2 L or larger graduated cylinder/beaker. This is for measuring the volume of water needed and pouring it into the bucket Created by Science Buddies for Genentech's Middle School Challenge Pilot Page 3

4 o Water (1 L per team) o Salt (35 g per liter) o Scale o Red food dye o Soil (1 Tbsp per L) o Measuring spoon, tablespoon size o Yard stick (wrapped for protection) or other long stirrer for mixing solution 500 ml plastic beaker with handle; this is for transferring exact volumes of "dirty" water to the team s test systems. Water meter that detects total dissolved salts (TDS) Volunteers (1+ per classroom). Volunteers will monitor students while they use the hot plates, for safety issues, and ask students thought-provoking questions as they develop and test their desalination designs. Instructions: Science Challenge Timeline Day Challenge Procedure Minutes into the Class Period 1: Preparation Collect and put out all materials and worksheets Before class 1: In class Introduce the challenge 0 10 Break into teams and have teams collect materials Design and build the desalination system * 2: Preparation Prepare enough saltwater for all teams Before class 2: In class Introduce volunteers. Review hot plate safety. 0 5 Start testing desalination system prototype Redesign and make final desalination system Test final desalination system Finish reflection sheets and clean up * * Note that this timeline is built around the smallest class period (80 minutes). Teachers with longer periods can adjust as they see fit, and all teachers may adjust as best suits their classroom and teaching style. Day 1 1. Challenge relevance and talking points: Discuss with students the importance of having clean drinking water, how this is an issue that affects many people, and how people need clean drinking water as a basic necessity and for both preventative and active health care. Also discuss how contaminated water can be purified through evaporation and the formation of condensation. The Providing Clean Water PowerPoint slide show can be used to help communicate these points. Here are some questions that may be useful for discussion: a. How many people in the world do you think lack access to clean water? b. What causes water to evaporate? Why is water vapor made out of purified water? c. How does condensation form? d. What are the key components of a simple desalination system? Created by Science Buddies for Genentech's Middle School Science Challenge Pilot Page 4

5 Day 2 Middle School Science Challenge Pilot: Providing Clean Water e. How can condensate be collected without also collecting contaminated water? f. Where might water vapor escape from in a desalination system? 2. Give students an overview of what they will be doing for the Providing Clean Water challenge. a. Explain to students that they will be put into teams to make a homemade desalination system. b. Each team will be given the same materials from which they can build their desalination system; show students the materials they will be using (and let them know there will be ice available on day 2 during testing). Inform them that they should use the large metal can (No. 10 tin can) for holding the saltwater, which will be heated on a hot plate, but the rest of their design is up to them. Be sure to emphasize that not all of the materials need to be used. c. Their system will be judged on how efficiently it makes clean, drinkable water and the materials costs associated with producing their desalination system. The quality of the collected water will be evaluated using a digital water meter (which will be shared between all teams in the class). d. The two class periods that the challenge is conducted in will be as follows: i. During the first class period, student teams will plan out their desalination design (using the Day 1 Worksheet). Once the team has a design, they can build it. As they plan and build their design, they should also fill out the Project Cost Tracking Table as a team for their prototype (i.e., first) desalination system. ii. During the second class period, they will follow and fill out the Day 2 Worksheet to test their system with 500 ml of saltwater, and then tweak or redesign their system in preparation for the challenge test. All teams will start the final purification challenge at the same time and be judged on how well that final system performs and the cost of materials used for it (as determined by filling out the Project Cost Tracking Table as a team for the final desalination system). After the challenge is done, students should fill out the Reflection Worksheet. 3. Break students into teams (with 3-4 students per team). Hand out a Day 1 Worksheet to each student and a Project Cost Tracking Table to each team. (While a given team will build a single desalination system and fill out a Project Cost Tracking Table together, each student should fill out their own worksheet.) Have students plan and build their desalination systems while individually filling out all of the day 1 questions on the worksheet, as well as filling out the Project Cost Tracking Table (for their prototype desalination system) as a team. 1. Prep work: Prepare 1 L of saltwater for each team to use. Each team will need 500 ml of just saltwater for their prototype test. For the final challenge test, soil and red food dye will be added to the saltwater in front of the students to create even more heavily contaminated water. This will model needing to take a laboratory-developed technology and running it against even harsher real-world conditions. To make the saltwater, combine the number of liters of water needed for all teams in the class (1 L per team) with 35 grams of salt per liter in the bucket. a. While preparing the saltwater, use the water meter to measure the parts per million (ppm) of the total dissolved solids (TDS) in the saltwater. It should be between 40,000 and 70,000 ppm. Record the exact value that the water meter gives so students can compare it to their condensation results later. 2. During class: Hand out a Day 2 Worksheet and a Reflection Worksheet to each student. Each team gets their desalination system and adds 500 ml saltwater to the system for prototype testing. Have students place their system on a hot plate, turn the hot plate to 500 C (maximum heat), and let the Created by Science Buddies for Genentech's Middle School Science Challenge Pilot Page 6

6 system be heated for 20 minutes. During this time, they should evaluate their own system for design flaws, and walk around the classroom and look at other teams systems, answering the questions in step 1 of their Day 2 Worksheet. 3. After their desalination systems have been heated for 20 minutes, have students turn off their hot plates. A teacher or volunteer can work with each team to check whether their systems collected any water. Caution: Because a lot of hot water vapor may have collected in the systems, teacher/volunteers should be especially careful when opening them. After the hot plates are turned off, have teacher/volunteers carefully open the lid of the large can to let built-up hot water vapor slowly escape, then use a plastic graduated pipette to measure how much condensation the desalination system collected (if any), and transfer the collected condensation to a 2 oz mini plastic cup. During this time, students should fill out steps 2-3 of their Day 2 Worksheet with their results. a. If a team collected 15 ml or more of condensation, they should measure 15 ml of condensation into the mini cup and use the water meter to measure the purity of the water in the cup. b. If a team collected between 4 ml and 15 ml of condensation, they should measure 4 ml of condensation into the lid of the water meter (up to the first line on the bottom) and carefully use the water meter to measure the water purity in the lid. c. If < 4 ml of water is collected, there is too little to assess the purity. 4. Have students tweak their desalination system, filling out steps 4-6 of their Day 2 Worksheet. Be sure students are careful when disposing of the hot water in their systems. During this time, if any team needs particular help redesigning their system, you may use your best judgment to decide whether that team should be shown the system designs in Figure 1 at the beginning of these instructions. 5. With at least 40 minutes to go in the class period, have the teams stop tinkering/testing and start the final challenge test. In front of the students, add soil (1 Tbsp per L) and red food dye (enough to brightly color the water) to the saltwater (there should still be enough saltwater left to give 500 ml to each team for the final challenge test). Explain that these represent additional contaminants and that sometimes a design encounters new and unexpected challenges in the real world. In the final challenge test they will see if the desalination systems they have created can handle these additional challenges. (Note that adding the food coloring and soil should not affect how pure the water is that students collect, unless the contaminated water is directly spilled into their collection cups.) a. While preparing the dirty saltwater, use the water meter to measure the ppm of TDS. 6. Distribute 500 ml of "dirty" saltwater (saltwater + soil + food coloring) to each team and have them repeat the challenge testing, as laid out in steps Once 20 minutes of testing are up and students have determined the quantity and purity of the water their final desalination system collected, have an adult (teacher or volunteer) fill out a Challenge Judging Rubric. Assigning points for each team on a board in the classroom may help keep all students interested in the results and allow an immediate declaration of the winning team(s). Students should record their team's results in step 7 of the Day 2 Worksheet. 8. Have each student fill out the Reflection Worksheet. Created by Science Buddies for Genentech's Middle School Science Challenge Pilot Page 6