Meddling with Melting 2nd Grade Weather Unit Sarah Rhodes-Ondi, ELC Naturalist Rain, snow and sleet freeze on the roads during the winter up north creating scary driving conditions. Drivers can slide on the ice causing accidents. As soon as the snow falls road crews set to work plowing the roads and trying to find a way to decrease the amount of ice and snow on the roads. One very common method to remove ice from roads is to apply salt to the roads. Why do the road crews add salt? Let’s find out! Steps of the Scientific Method 1. State Problem What question are you trying to answer by doing this experiment? Write “Does salt decrease the time that it takes to melt ice?” in #1 on your Laboratory Form. 2. Do Research Read about your topic in books. Talk to experts. Observe the real world. Become the expert! Write anything you learn that will help you plan and explain your experiment in #2 on the Lab Form. 3. State Hypothesis Based on your research, make an educated guess about what will happen when you do your experiment using what you learned from your research (#3 Lab Form). This should be written with a prediction and not in question form. 4. Design Experiment Independent Variable: What factor (treatment) are you testing? Hint: salt. Dependent Variable: What will you measure or observe? Hint: time it takes for cubes to melt. Can you think of something else you could measure? What could you use a ruler for? What could you use a thermometer for? Control: What is something you will not change at all? Hint: not add salt to some ice cubes. Replication: How many replicates will you do? Scientists run a minimum of 5 in case they make a mistake. Hint: Each cube is 1 replicate in this experiment. Record all of these in Lab Form #4. 5. List Materials Recorded in Lab Form #5. Each group will have 1 full set of the materials below. 2 paper towels 10 ice cubes per group (5 for control, 5 for treatment) Salt Plastic spoon for measuring nearly 1 tsp. 2 thermometers Stop watch or clock 6. Test Hypothesis Procedure: Do experiment! o Record the list of steps below in Lab Form #6. o Place the ice cubes equal distant apart on the paper towels or hard surface. Keep all the cubes you will add salt to on the right and all the rest on the left. o Add 1 tsp of salt to half of the ice cubes. o Observe the ice cubes melt for 10 minutes. Record your observations in Lab Form #7. o Take a break and come back in 20-25 minutes to check on your experiment. Record the time each cube melts in Lab Form #7. o Wave hand over the top of the melting cubes. What do you feel? If you have 2 thermometers place one alongside one of the cubes with salt on it and the other along one of the cubes without salt on it. Record the temperature of each cube. 7. Analyze Results Which cubes melted faster? Record in Lab Form #8. 8. Draw Conclusions Record in Lab Form #9. Did you support your hypothesis? Why? Why do you think there a big puddle of water on your desk? Was the ice solid or liquid? Was the puddle solid or liquid? Which season has icy road conditions? What did you learn? How could you change the experiment next time you run it? Lab Form 1. State the Problem 2. Research 3. Hypothesis 4. Design Experiment 5. Materials 6. Test Hypothesis 7. Data Collection a. Observations: b. Salty Cube Time No Salt Cube Time c. d. e. f. g. 8. Analysis of Results 9. Draw Conclusions Notes for Teachers: There are many ways to explain this experiment to your students. You can teach the kids that they use salt to melt ice on the roads in temperate climates during the winter. It is one way people can make conditions safer for drivers following bad weather. The chemistry explanation: The salt is decreasing the freezing point (freezing point depression). This means that the temperature has to be colder for the ice to freeze if salt is applied to it (Figure 1). Under freezing conditions, adding salt allows road workers to make the ice melt. Another way to explain this experiment is that the salt actually decreases the temperature needed to melt the ice. The rate of ice melting is faster with the salty cubes because the solute content is increasing. It can be said that the salt actually shoves itself between the water molecules. Use the smallest, uniformly sized, ice cubes you can find or make some. The typical size that comes out of refrigerators takes 40-48 min to melt with salt added and over an hour to melt without. This is a laboratory that can be started at the beginning of a class period and finished towards the end of class. The experiment does need to be taken to the end if possible so the kids get a chance to collect data and analyze it. Without the kids collecting the data from both the treatment and the control group it is just a demonstration. The experiment is written so that each group can do all 5 replicates themselves. The experiment can be altered so that each group completes one replicate (adds salt to one ice cube and does not add salt to another) as long as the class has at least 5 groups completing 1 replicate. Emphasize the importance of each group adding the same amount of salt and using the same sized ice cubes so the kids realize that this is the only way each group can carry out a true replicate of the experiment. Water Water + salt Melt Melt 0°C 0°C Freeze point Freeze point Figure 1: Shows the freezing point depression that occurs by adding salt to the ice cubes. = Freezing point References http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/meltpt.html http://van.physics.illinois.edu/qa/listing.php?id=14230 Sunshine State Standards “Meddling with Melting” addresses big concepts of seasonality in weather conditions, measuring temperature and weather patterns taught during the first 9 weeks of the school year. Benchmarks Description Science SC.2.E.7.1 Compare and describe changing patterns in nature that repeat themselves, such as weather conditions including temperature and precipitation, day to day and season to season. SC.2.N.1.4 Explain how particular scientific investigations should yield similar conclusions when repeated. SC.2.N.1.6 Explain how scientists alone or in groups are always investigating new ways to solve problems. SC.2.N.1.5 Distinguish between empirical observation (what you see, hear, feel, smell, or taste) and ideas or inferences (what you think). SC.2.N.1.2 Compare the observations made by different groups using the same tools. SC.2.P.8.4 Observe and describe water in its solid, liquid, Math and gaseous states. MA.2.A.4.3 Generalize numeric and non-numeric patterns MA.2.G.5.2 using words and tables. Identify time to the nearest hour and half hour.
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