Activities
Pre-assessment
To gain a baseline of the students' abilities to apply the scientific concepts from the previous unit about density, phase change, and solubility, students will be given a mixture of dark drink powder, small wax shavings, iron filings and zinc granules and asked to separate the mixture and describe the properties of the components. The students will have access to beakers, plastic bag covered magnets, water, tweezers, a thermometer, ice and an electronic balance. Some of the materials are not necessary and in the mix as spoilers so that the tools provided do not lead the students to the conclusion. Each student will have to come up with their own procedures and document their actions and findings. The procedures documented and properties of the materials described to show how much the students understand the use of density, solubility, and insolubility to separate materials.
For homework, the students will record their actions to save the environment. Showing how much they already contribute to the single stream recycling effort in Delaware and will apply the lessons learned to our next unit of study: Watersheds.
Responsible Citizenship and Inquiring Minds
Focus Question: What am I doing to save the environment? What happens as a result of my actions (particularly in the area of recycling)?
To catch the student's attention, I will enter the room in a white sheet hanging over my clothes like a toga with cans, papers, and plastic pinned to it and dark marks smeared in places. On my head will be a ring of plastic ivy. On my face, I will also have a dark mark. In a cheerful, but slightly raspy voice, I will introduce myself as Mother Earth and ask the students to share with me the things they are doing to help me since I provide so much for them. Documenting their actions on the board, I expect that they will mention recycling almost immediately because we recycle in our classroom. After the students have exhausted their accomplishments, we will discuss the ways in which their actions help Mother Earth. I will ask them to explain the consequences of the choices they made. I will leave recycling to last. In my class, we are lucky enough to have an interactive white board. Starting a new page, we can use it as a reference as we learn about single stream recycling. This can also be done on a large sheet of paper and posted in the room. I will assess what knowledge the class has about what happens to the materials they recycle. I will question every step and write down their hypothesis and prior knowledge whether correct or not.
To conclude this lesson, I will show them the Introduction video on www.explorethecycle.com. It is only 50 seconds long. Like all videos in my classroom, we will watch it multiple times, so students can have a chance to take in the video as a whole and enjoy the content and then focus on specific components when they re-view. This is similar to the rereading strategy promoted to improve comprehension. The exit ticket for this lesson is to write three things important in the video, two behaviors the student thinks they might want to try to help the environment and one behavior they already do to save the environment. Though I asked for some of this information in the previous night's assignment, the rate for homework completion for most of my students is horrendous, so to get information from all students I require them to write it in class. The previous night's assignment was to start them thinking so they would have something to contribute when I asked for their environmental actions in class.
Plastics Density Separation
Focus Question: If we throw everything into one large pile, how can it then be separated to be reused?
To catch the students attention, I will enter the room with 8 trash bags (the number of lab groups I have) full of cleaned waste to be recycled. Caution: sterilize the recyclables and watch for exposed sharp edges on open metal cans. I will dump one on each lab table and ask the students what do we do with the comingled recyclables that have been brought to the MRF? The class will hypothesize solutions. With a little guidance, the first conclusion needs to be that separating the materials makes them valuable to companies who need them. After that conclusion, list all possibilities on the board. Take this time to brainstorm, not to evaluate. I will make the students explain their methods in some detail. If the students mention automation or machines, I ask them how a machine could tell the materials apart? What would the machine do to distinguish and move one type of material and not another? Next we will discuss the advantages and disadvantages of each option. For example, the obvious solution is to have someone pick through and separate the different types into bins. An advantage to this process is the ease to initiate the program: just hire a few people and get to work. A disadvantage is the material arriving at the MRF is not clean, though the samples in front of the students will be. There are health safety issues with using manpower. Additionally, manpower can only go so fast, and it is expensive over time: health insurance, pensions, not to mention paying numerous employees every week.
After the students have gone through their idea list, I will help guide them to the conclusion that a products specific properties identify what it is made of. I will show the students the second section of www.explorethecycle.com video "MRF." I will stop the video at 31 seconds and ask the students how the v-screen separation works. I will replay the video from the 10 second to the 31 second mark as often as they need. The answer is density. With the students help I will list what is left in the stream and what might work with the next material, steel, iron and tin cans. We will watch the video from the 31 second mark to the 1:03 mark and discuss what was used for both the ferrous and the nonferrous metals. Again we will watch the video as often as necessary. I will have the students note that the property used for the metals was not density but magnetism and reaction to an electrical field. We will start to make a list of the properties. We will watch the rest of the MRF video and I will describe to the students that the sensor that detects the plastics is a combination of infrared sensor and optic sensor. The infrared sensor often misidentifies plastics as other materials because of the coloring of the plastic and any labels or caps left on the bottles. The optic sensor compensates for this deficiency but does not operate well alone either. However, the combination is effective. We will discuss the properties used to separate the plastics and the glass (more dense, not magnetic, does not react to electricity or infrared energy). We will add them to the list and review the ways the students suggested for separation and point out that though the video only detailed one option, there are many systems available.
Then we will watch the plastic segment of www.explorethecycle.com. I will make sure to stop at the 15 second mark and explore the different types of commonly available plastics. I will note that the video does not tell how the machine separated one type from another. After the video, we will clear the recyclables off the table, and I will give the students a container of mixed polymer pellets. 42 If you make your own mix, make sure the densities of the plastics do not fall in the exact same range and that the different types of plastics are different colors. This still allows the students to use manual separation as an option and to discuss the difficulties of the process. I will explain to the students that their task is to separate all the plastic pellets they were given into groups. They must document the exact process they use and record their results. I will offer the students beakers, tweezers, mini-cups, water, salt, magnets, and flashlights. Most likely the students will not finish planning the separation and their experiment will carry over to a second day.
Plastic pellets are hydrophobic and attract air bubbles; so if students use the property of density to separate, some pellets will continue to float despite having a greater density than the water. I will help the students explore ways to deal with this problem. Some suggestions are agitate the water, gently poke all the floating pellets at the surface, or pour the water over the plastics rather than pour the plastics into the water. I will encourage the students to note all the things they try and their success. Close to the end of the second class, whether the students have successfully completed the task or not, we will stop and discuss the students' choices and their results. We will make sure to discuss the advantages and disadvantages of the chosen systems and chart them with the students. At the end of the period, students will write about properties of the plastic pellets and which properties they used to separate the material.
Phase Change: Reading the Graph
Focus Question: How do old cans, bottles and jars become new materials?
For this lesson, students will watch the plastic, glass and metal sections of www.explorethecycle.com determining how the processes are similar. Then they will determine the temperatures at which aluminum, tin, iron and steel change phase using graphs (see Appendix E). Prior to class, I freeze flakes of wax in water. To make the activity more authentic, the water will be frozen in one shape, and I will tell them that I need the ice in another shape, but without the impurities. I will provide beakers, thermometers, hot plates, funnels, filters, and ice trays. The groups with develop procedures and perform their experiment. The last 10 minutes of class, we will discuss the procedures they used and if any problems developed. I expect to see a few groups trying to melt the ice-wax mixture with the hot plates and melting the wax when they only intended to melt the ice. We will discuss how to overcome these difficulties and their exit ticket will be explaining how the lab connected to recycling metal, glass and plastic.
Solubility and Deinking
Focus Question: Why does the ink come off?
In this lesson, students will experiment with different solvents for inks. Using chromatography paper, students will mark on separate papers with an overhead marker, a water-soluble art marker, a permanent marker, ballpoint pen, and dry erase marker. After talking about the properties of chromatography paper, I will offer them possible solvents to try: water, isopropyl alcohol, and hydrogen peroxide. If students make other suggestions, we will try to find them in the building if they are safe to use without a ventilation hood (I don't have one in my classroom). Students will then experiment and document what happens with the methods they choose. The students will stop ten minutes before the end of class to share their results and analyze what happened and why it happened. The exit ticket of the day is to answer the focus question. If students wish to investigate this topic further and suggest other solvents and inks, we may start the class the next day investigating their suggestions.
Insolubility and Papermaking
Focus Question: How is paper recycled? How is the ink separated from the paper? How is an old sheet of paper changed into a clean new sheet?
To focus the class, I will show them some examples of recycled paper (printer grade paper to art paper). We will watch the paper segment on www.explorethecycle.com and discuss the process presented in terms of solubility. The class will then make paper according to the directions on the National Wildlife Federation website, www.nwf.org/forests/papermaking.cfm. The exit ticket will be to draw a cartoon of the papermaking process describing how solubility and insolubility helped separate the ink and the pulp suspension and remake paper. If students cannot finish the assignment, they may turn it in the next day. This lesson will most likely take two days.
Post-assessment and Plan
After completing the unit, I will give the students another mixture and ask them to work independently to separate the components. This mixture will include small pieces of PET milk bottles, iron fillings, powdered tea mix and small pieces of HDPE soda bottles. I will give them the same lab materials as pre-assessment, and they must write out their procedures and document the properties of the materials they find. The post-assessment will be compared to the pre-assessment. The students will reflect in their science notebooks about what they learned.
For homework, they will confer with their families and come up with a signed agreement about what they will do to help the recycling effort. This cannot be an action they already do. As a class, we will come up with possibilities. 43 In this manner, the unit will not just be the acquisition of knowledge and development of critical thinking and investigation but also to increase the students' citizenship.
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