Separating the Mixture

Transcription

1 Separating the Mixture 40- to 1 50-minute session ACTIVITY OVERVIEW I N V E S T 5 I O N I G AT Students perform their procedures written in Activity 3, A Plan to Separate the Mixture, to physically separate the solid and liquid components of mixture. After completing the activity, they evaluate their procedures and make changes to improve their plans. Students begin recording information about each of the substances in the mixture on a Chemical Data Sheet which will be used throughout the unit to help record evidence that will help identify the substances. KEY CONCEPTS AND PROCESS SKILLS (with correlation to NSE 5 8 Content Standards) 1. Substances have characteristic properties, such as density, that are independent of the amount of the sample. (PhysSci: 1) 2. A mixture of substances often can be separated into the original substances using one or more of the substances characteristic properties, such as density. (PhysSci: 1) 3. Students design and conduct appropriate scientific procedures. (Inquiry: 1) KEY VOCABULARY mixture A-53

2 Activity 5 Separating the Mixture MATERIALS AND ADVANCE PREPARATION For the teacher * 1 overhead projector * 1 Material Safety Data Sheets (MSDS) booklet from Issues and Physical Science kit 1 transparency of Student Sheet 5.1, Chemical Safety Data Sheet 1 Scoring Guide: DESIGNING INVESTIGATIONS (GI) (optional) 1 transparency of Group Interaction Student Sheet 1 Evaluating Group Interaction For the class * 1 liquid waste container For each group of four students ml (9 oz.) plastic cup with lid containing unidentified mixture, from Activity 3 2 pairs of plastic forceps 2 droppers 1 funnel 2 pieces of filter paper 1 piece of steel wool 1 metal screen 1 SEPUP tray ml (3 1 / 4 oz.) plastic cups with lids 1 cup of water * paper towels * access to hot soapy water For each student * 1 pair of safety goggles 1 copy of separation plan from Activity 3 1 Student Sheet 5.1, Chemical Safety Data Sheet 1 Scoring Guide: DESIGNING INVESTIGATIONS (GI) (optional) 1 Group Interaction Student Sheet 1 Evaluating Group Interaction (optional) *Not supplied in kit Masters for Group Interaction Student Sheets are in Teacher Resource II: Diverse Learners. Masters for Scoring Guides are in Teacher Resources III: Assessment. A-54

3 Separating the Mixture Activity 5 Student Sheet 5.1, Chemical Data Sheet will be used again in Activities 6, 7, and 10. Designate a place in students notebooks, or in the classroom where they can be kept so that they are accessible during subsequent activities. If you are conducting this activity with multiple classes, be prepared to pour the separated parts back together into the 9 oz. cups to reconstitute the mixture for the start of each class. Replenish any mineral oil, iron nitrate solution, or solids that were lost. The mixture contains mineral oil. Any item that comes into direct contact with the mixture will retain an oil residue. Lab equipment, such as SEPUP trays and droppers, must be thoroughly cleaned with hot soapy water to remove this residue. Have lots of hot soapy water on hand for students to use to wash equipment when their separation is complete, and when you need to clean supplies for additional classes. If students plan to incorporate additional supplies into their separation plans, remind them to bring in the supplies they will need once you have approved their use. SAFETY The chemicals used in this activity may cause skin irritation. Use caution when handling solutions. Always wear safety goggles, and thoroughly rinse any area that comes into direct contact with laboratory chemicals. Make sure students rinse their hands when they are done working with the components of the mixture. TEACHING SUMMARY Getting Started 1. Review students procedures to physically separate the unlabeled mixture. Doing the Activity 2. (GI ASSESSMENT) Students carry out their separation plans. Follow-Up 3. Students record information about each substance on a Chemical Data Sheet. 4. The class evaluates the separation plans. A-55

4 Activity 5 Separating the Mixture TEACHING SUGGESTIONS GETTING STARTED 1. Review students procedures to physically separate the unlabeled mixture. Ask students to review their separation plans from Activity 3. Review the safety precautions students should take, including not handling waste directly with their bare hands, wearing goggles and aprons, cleaning up all spills immediately, and washing their hands when they complete the laboratory. Remind students that they should treat the mixtures as hazardous until they can identify from what it is composed. In this activity, students work in groups to conduct the procedure they designed in Activity 3, A Plan to Separate the Mixture. Their purpose is to separate the components so that they can identify them for appropriate handling and disposal. Remind students that this was one approach modeled by the hazmat team in the DVD: once they were able to identify some of the unknown substances in the barrel, the team referenced Material Safety Data Sheets (MSDS) to determine the potential hazards, how to handle them and how to appropriately dispose of them. Show them the MSDS sheets that accompany the kit to familiarize them with the information contained on such sheets. DOING THE ACTIVIT Y 2. (GI ASSESSMENT) Students carry out their separation plans. Distribute the materials available to your students for the separation of the substances. Allow them time to work with their groups to follow their separation plans. As students work to separate the components of the mixture, observe their work, and monitor their progress. Allow them to make mistakes and encourage them to make and record adjustments as they conduct the procedure. Stress the importance of trying out their proposed plan and evaluating its effectiveness, just as scientists would. The group work in this activity provides an opportunity to score students with the GROUP INTERACTION (GI) Scoring Guide. You may score them as you observe how they work and then provide feedback using the scoring guide. You may additionally ask them to score themselves. Pass out Group Interaction Student Sheet 1, Evaluating Group Interaction to guide students in reflecting on their group work. When students complete their work separating the mixture, they should have one small cup of solids that have been rinsed, cleaned, and dried, one small cup of clear liquid (mineral oil), and one small cup of orange liquid (iron nitrate solution). The purity of the samples will depend on students work. At the end of the activity, the three small cups will be returned to you. When cleaning up, direct students to pour any liquid waste they generated into a designated waste container and not down the drain. This is essential since the identity of the mixture has not been established. The materials will have mineral oil on them, and so have plenty of hot soapy water ready for students to wash their equipment properly when they complete the separation. For the next class, recombine the components of the three cups to remix the mixture. It is recommended that you do this once students have left the room. You will provide fresh samples of each of the liquids for students to work with in Activity 6, Identifying Liquids. FOLLOW- UP 3. Students record information about each substance on a Chemical Safety Data Sheet. Once student groups have isolated the substances in the mixture, each student will start recording information about each substance on Student Sheet 5.1, Chemical Safety Data Sheet. This sheet will serve as a record of the information gained in Activities 5, 6, 7, and 10 for each substance. The information will then be used to identify the substance, and the record the hazards associated with each. These sheets model the documentation process a hazmat team would use as they obtained evidence about an unlabeled substance. A-56

5 Separating the Mixture Activity 5 Before filling out the sheets, review the categories and explain any that are not clear. Show students the MSDS booklet included with the kit and explain that the Chemical Data Sheets they will keep are similar to the MSDS sheets provided in the kit. MSDS sheets were also shown in the Hazardous Materials DVD segment in Activity 1, Handling Hazardous Materials, as the hazmat referenced them once the contents of the unidentified barrel were identified. MSDS sheets provide information about handling, storage, and disposal of potentially hazardous substances. Demonstrate how to fill out information for each type of substance isolated on Student Sheet 5.1, Chemical Safety Data Sheet. For reference purposes, the class will need to establish a common name for each of the substances. Such as black square or light metallic cylinder. Stress the importance of establishing a common name, and model how to fill in the initial information on Student Sheet 5.1. At the end of this activity, students will be able to fill in Appearance based on their initial observations of each type of substance. As students fill out the information on the sheet, encourage them to be as descriptive as possible when making observations, and as accurate as possible when recording data and calculations. Identify a place in the classroom where the sheets will be kept, or a place in students notebooks where they will be accessible for the duration of the unit. 4. The class evaluates the separation plans. Ask the class, What obstacles did you encounter while separating the mixture? They might indicate that completely isolating the liquids from each other without contamination was difficult, and that there was an oily residue left on the solids that is difficult to remove. Write students responses on the board. Ask, What changes did you make to your separation plan while separating the mixture? They might also indicate that it was hard to use the tools (plastic forceps, droppers) required for safety, since they are new to using them and they needed to become more familiar with the tools. Or perhaps they needed to add an additional step such as rinsing the coating off of the solids that they did not realize was needed at the time of writing the procedure. Analysis Question 1 asks students to add changes to their procedure as if they were going to perform the separation again. This provides an opportunity for reflection, and to stress that the alteration of a procedure to meet a specific goal is sometimes necessary. This icon indicates questions for formative assessment. See Teacher Resources III: Assessment for more information. Analysis Question 3 is a quick check formative assessment opportunity. Use this question to gauge students understanding of methods to physically separate a mixture. If students are struggling in answering this question, provide additional instruction. SUGGESTED ANSWERS TO QUESTIONS 1. What changes did you have to make to your separation procedure while you were performing the procedure? Why? Students may have added steps to their procedures, such as use plastic forceps to lift the metal screen and use steel wool to scrape off solids. Students may have encountered unexpected difficulties and had to change materials or procedures; or they may have described unnecessary steps, such as moving the solids from one container to another several times. 2. What safety precautions did you take while working with the unidentified mixture? Student answers will vary, but should reflect the steps they incorporated into their separation procedure. Theses may include wearing goggles and an apron, not directly touching any of the items from the mixture, and additional safety measures from the class safety guidelines. Students should be sure that these are included in their Separation Plan. A-57

6 Activity 5 Separating the Mixture 3. How would you separate: a. oil and vinegar Since the oil is less dense and floats on top of the vinegar, use a dropper to remove the oil from the top of the vinegar. Another option is to pour off as much of the oil as possible. b. salt and iron shavings Use a magnet to isolate the iron from the salt. They might also suggest using a sieve, depending on the size of the pieces, or adding water to dissolve the salt and then letting the iron settle to the bottom. Then the saltwater can be poured off, and the solution set out so that the water evaporates, leaving behind the salt. c. salt and sand Add water to the mixture. Mix well. This will dissolve the salt in the water. Then pour the solution through a filter. This will separate out the sand. Additionally, the water can be evaporated separately, leaving behind the salt. A-58

7 Name Date Chemical Data Safety Sheet 2007 The Regents of the University of California Substance Material Physical Hazards Safety Precautions Charachteristics Appearance Density Corrosive/ Flammable Toxic Reactive Liquid A Liquid B Red tube Black square Light metal cylinder Dark metal cylinder Issues and Physical Science Student Sheet 5.1 A-59

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