7 th Grade Fall 2018 Lesson Plans. Vanderbilt Student Volunteers for Science

Transcription

1 7 th Grade Fall 2018 Lesson Plans Vanderbilt Student Volunteers for Science

2 VOLUNTEER INFORMATION Team Member Contact Information Name: Phone Number: _ Name: Phone Number: _ Name: Phone Number: _ Name: Phone Number: _ Name: Phone Number: _ Teacher/School Contact Information School Name: Time in Classroom: Teacher s Name: Phone Number: VSVS INFORMATION VSVS Director: Pat Tellinghuisen (W), (H) patricia.c.tellinghuisen@vanderbilt.edu VSVS Office: Stevenson Center 5234 Co-Presidents: Christina Wang christina.e.wang@vanderbilt.edu Arunabh Singh arunabh.singh@vanderbilt.edu Secretaries: Gabriela Gallego gabriela.l.gallego@vanderbilt.edu Sabeen Rehman sabeen.rehman@vanderbilt.edu Vanderbilt Protection of Minors Policy: As required by the Protection of Minors Policy, VSVS will keep track of the attendance who goes out when and where. Before You Go: The lessons are online at: the teacher prior to the first lesson. Set a deadline time for your team. This means if a team member doesn t show up by this time, you will have to leave them behind to get to the school on time. Don t drop out from your group. If you have problems, Pat or one of the co-presidents, and we will work to help you. Don t let down the kids or the group! If your group has any problems, let us know ASAP. Picking up the Kit: Kits are picked up and dropped off in the VSVS Lab, Stevenson Center The VSVS Lab is open 8:30am 4:00pm (earlier if you need dry ice or liquid N 2). Assign at least one member of your team to pick up the kit each week. Kits should be picked up at least 30 minutes before your classroom time. If you are scheduled to teach at 8am, pick up the kit the day before. There are two 20 minute parking spots in the loading dock behind Stevenson Center. Please do not use the handicap spaces you will get a ticket. While you re there Just relax and have fun!

3 New Member Orientation New Member Orientation Team Leader Training Team Leader Training Team Member Training (Mini Lessons) Team Member Training (Mini Lessons) Class Visits: Week 1 (Mini Lessons) Class Visits: Week 1 (Mini Lessons) Team Member Training (Remaining Lessons) Team Member Training (Remaining Lessons) Fall Break Fall Break Class Visits: Week 2 Mega Microbe Day Class Visits: Week 3 Class Visits: Week 3 Class Visits: Week 4 Class Visits: Week 4 Class Visits: Week 4 Makeup Week Makeup Week

4 CLASSROOM ETIQUETTE Follow Metro Schools Dress Code! No miniskirts, shorts, or tank tops. Tuck in shirts if you can. Please dress appropriately. Metro student standard attire guideline: COLLEGE Q&A SESSION VSVS members should be candid about their experiences and emphasize the role of hard work and a solid body of coursework in high school as a means to get to college. the teacher prior to the first lesson. o They may want to have the students write down questions prior to your lesson. o They may also want to have a role in facilitating the discussion. Finish the experiment of the day and open up the floor to the students. Remind them of your years and majors and ask if they have specific questions about college life. If they are shy, start by explaining things that are different in college. o Choosing your own schedule, dorm life, extracurricular activities, etc. o Emphasize the hardworking attitude. The following are some sample questions (posed by students): When is bedtime in college? Does your mom still have to wake you up in college? How much does college cost? What do you eat in college and can you eat in class in college? How much homework do you have in college? DIRECTIONS TO SCHOOLS H.G. HILL MIDDLE SCHOOL: 150 DAVIDSON RD HG Hill School will be on the right across the railroad lines. HEAD MAGNET SCHOOL: 1830 JO JOHNSON AVE The parking lot on the left to the Johnston Ave. J.T. MOORE MIDDLE SCHOOL: 4425 GRANNY WHITE PIKE From Lone Oak, the parking lot is on the right, and the entrance into the school faces Lone Oak, but is closer to Granny White. MEIGS MIDDLE SCHOOL: 417 RAMSEY STREET Going down Ramsey Street, Meigs is on the left. ROSE PARK MAGNET SCHOOL: th AVE SOUTH The school is located on the left and the parking is opposite the school, or behind it (preferred). WEST END MIDDLE SCHOOL: 3529 WEST END AVE Parking is beside the soccer field, or anywhere you can find a place. Enter through the side door. EAST LITERATURE MAGNET SCHOOL: 110 GALLATIN AVE Going down Gallatin Avenue, East Literature Magnet School is on the left.

5 VANDERBILT STUDENT VOLUNTEERS FOR SCIENCE Chemistry in a Ziploc Bag (7 th Grade) Mini Lesson for Fall 2018 GOAL: To use the scientific method to explain observations made when calcium chloride, sodium bicarbonate, water, and phenol red are mixed. Fits TN State standards: 7.PS1.2, : 7.PS1.3, : 7.PS1.4: 7.PS1.5 LESSON OUTLINE I. Introduction Explanation of the scientific method and the importance of observations. II. Experiments A. Experiment: Students observe the changes that occur when four different substances are mixed. B. Using the Scientific Method. Students brainstorm how to determine the roles of the different reagents. C. Applying the Scientific Method. Students observe what happens when just two reagents react, then 3 reagents and then all four. III. Observations and Explanation IV. VSVS Background Information on Chemical Equations 1. In the car ride before the lesson, read through this quiz together as a team. Make sure each team member has read the lesson and has a fundamental understanding of the material. Lesson Quiz 1. Why are scientific observations important? Why do they need to be recorded? 2. What happens when calcium chloride is added to the baking soda and then phenol red solution? 3. What are some of the possible student observations? How can they be explained? 4. What must scientists do when changing variables in an experiment? 5. What evidence of chemical reactions was observed? 2. Here are some Fun Facts for during the lesson: 1. Phenol red - It is used to test the ph of swimming pools. It is sometimes called guardex solution #2 - It is used to monitor the ph of cells in cell culture. An excess of waste or bacterial contamination will cause the media to become acidic and the phenol red will turn yellow. 2. Calcium chloride - It is put on roads in winter because it lowers the freezing point of water, preventing ice from forming. - The extremely salty taste of calcium chloride is used to flavor pickles. 3. Baking soda, or sodium bicarbonate - Why is baking soda used in baking? Baking soda reacts with acids in cake or cookie mixes to create carbon dioxide (similar to this experiment!) which creates bubbles that make the batter to expand ( rise ). - It can neutralize acids and is used to treat indigestion, heartburn, and burns. - It is an ingredient in some toothpastes, mouthwashes, deodorants and shampoos. - Some types of fire extinguishers use baking soda to put out fires

6 MATERIALS Note: Be sure you have all of the materials before you leave the lab. 12 plates 12 1 oz cups marked at the 15 ml level 15 Ziploc sandwich bags containing one teaspoonful of baking soda ml container of phenol red solution 12 dropper bottles phenol red 10 extra Ziploc sandwich bags 12 jars CaCl 2 12 jars NaHCO 3 12 stirrers 12 bottles water (100ml) 12 thermometers 24 taster spoons 25 paper towels 12 sets of 1 test tube rack and 3 test tubes 1 trash bag pencils (students use their own and need to have them ready to record observations) 1 PowerPoint/binder containing ppt, 36 Observation Sheets I. Introduction Organize students in threes Give each student an Observation Sheet. While one VSVS member gives the following explanation, other VSVS members should pour phenol red solution in the 13 1 oz cups marked at the 15 ml level. Explain to the students that all scientific knowledge is a result of careful investigation and observations. New discoveries and advances in science depend on having a careful and accurate record of observations made while investigating a question. That is why it is important to make accurate and detailed observations. Following observations, scientists make a hypothesis, or try to explain their observations. They then design an experiment that tests their hypothesis. NOTE: Phenol red solution is an acid-base indicator which turns purple in a basic solution and yellow in an acidic solution. II. Making Observations When Calcium Chloride Is Added To Baking Soda/Phenol Red Solution Learning Goals: Students record observations during chemical reactions IIA. Experiment Students do the Experiment in a Ziploc Bag Write the following chemicals on the board: sodium bicarbonate NaHCO 3, calcium chloride CaCl 2, water H 2 O, phenol red Ask students: How can you tell when a chemical change has occurred? Tell students what evidence to look for to determine if a chemical reaction occurs: a color change, a gas given off, temperature change, formation of a precipitate or a new chemical substance is formed. Give each group (of 3) one Ziploc bag containing baking soda, one 2 oz cup containing 15 ml of phenol red solution, and one plate. Tell students write down their observations. Your Notes:

7 Instruct the students that one person will be holding the bag while the other will write down all observations possible. Tell students to: 1. Hold the bag upright over the plate. 2. Open the bag and add a teaspoon of calcium chloride. 3. Add the phenol red solution (includes water) to the bag and seal the bag. 4. Gently shake the contents of the bag while holding the bag over the plate. 5. Ask students what they observe. Record students observations about color changes, temperature changes (is the bag cold or warm or both since there can be localized heating), changes in bag size, and gas given off or foaming. 6. The reaction takes about three to five minutes. NOTE: There is no danger of the bag exploding if the correct amounts of chemicals are used. Since everything is pre-measured, you should have no problems. In the event one does explode or leak, use paper towels to clean up any mess. If you have followed your directions, any spilled liquid will be on the plate, which can be easily wiped up with paper towels. Assure the students that the chemicals are safe. Write student observations on the board. Possible Student Observations: (1) When calcium chloride was added to the baking soda, nothing happened. (2) When the phenol red indicator in water was added to the baking soda/calcium chloride bag, the color started changing from red to yellow (some students may say they saw some pink color accept this as well.) (3) The bag became cold (for a short time). (4) The bag may be warm in some spots. (5) The bag fills up with gas. There are bubbles. (6) The bag may become cold again after a while. Ask students: What evidence for chemical changes did they observe in today s experiment? 1. A color change 2. A gas given off (this is a new substance) 3. Temperature changes 4. A white precipitate that is not obvious until the final mixture is allowed to settle out for some time. Your Notes:

8 II. Experiment B Brainstorming To Determine the Roles of the Different Reagents in the Reaction. Learning Goals: Students use the scientific method to design an experiment. Write the overall equation on the board: 2NaHCO 3 (aq) + CaCl 2 (aq) -----> CaCO 3 (s) + 2NaCl (s) + H 2 O(l) + CO 2 (g) For this section, students will brainstorm how to determine the role of each of the chemicals Tell students that this cannot be easily determined by observing the reaction with all 4 chemicals, but it can be determined by systematically testing different combinations of reagents. Tell students that they will determine which combination of chemicals produced the following observations: 1. The bag feels cold(er). 2. The bag feels warm(er). 3. The mixture fizzes, and the bag fills up with gas. 4. The mixture turns from red to yellow. Take the students through the steps of a systematically designed procedure to test each observation by taking one reagent (called the CONSTANT) and adding another reagent (called a VARIABLE), one at a time. Once they are done with that variable, they will go on to the next one until all possible combinations are tested. Tell students that scientists design experiments that change only one variable at a time. Make a list on the board (see below). Tell students that the first set of combinations of chemicals will involve sodium bicarbonate. Ask: What other chemicals should be added to sodium bicarbonate (one at a time) to investigate the observations made? (Refer to the chemicals written on the board see above). Note: When coming up with the list, you will come up with combinations that are the same as previous ones formed. In that case, CROSS IT OUT ON THE BOARD, and let students know that they do not have to test it because it would mean repeating an experiment. (Those that are repeated have strikethrough below). A. If sodium bicarbonate is the CONSTANT what different chemicals can be added to change the experiment?" 1. NaHCO 3 plus water 2. NaHCO 3 plus water plus phenol red solution 3. NaHCO 3 solid plus CaCl 2 solid B. Continue building the list with CaCl 2 as the constant: 4. CaCl 2 plus water 5. CaCl 2 plus water plus phenol red solution 6. CaCl 2 plus NaHCO 3 BUT this is already listed in #3. C. Continue building the list with water (H 2 O) as the constant: 7. H 2 O plus NaHCO 3 BUT this is already listed in #1. 8. H 2 O plus CaCl 2 BUT this is already listed in # H 2 O plus phenol red Tell them that they will also need to do an experiment with a combination of three reagents. Write it on the board. 10. NaHCO 3 plus CaCl 2 and water (no phenol red indicator added) Your Notes:

9 IIC. Experiment: Students Make Observations When Controlling the Number of Reagents. Pass out the following materials to each group of 3: 1tube rack and 3 test tubes 1 jar NaHCO 3 solid 1 jar CaCl 2 solid 1 bottle water (100ml) 2 spoons 1 stirrer 1 thermometer 1 tissue Experiments Demonstration by VSVS team Experiment 1in test tube 1 Experiment 2 1in test tube 1 Experiment 3 1in test tube 2 Experiment 4 1in test tube 2 Experiment 5 1in test tube 3 Experiment 6 1in test tube 3 Experiment 7 1in test tube 3 Experiment 8 in a plastic bag Reactants (calcium chloride, sodium bicarbonate, phenol red, and water) H 2 O plus phenol red solution NaHCO 3 plus H 2 O Add a squirt of phenol red to previous test tube CaCl 2 plus H 2 O Warning students must use 1small spoon only Add a squirt of phenol red to previous test tube NaHCO 3 plus CaCl 2 CaCl 2 plus NaHCO 3 plus H 2 O Add a squirt of phenol red to previous test tube CaCl 2 plus NaHCO 3 plus H 2 O plus phenol red solution in plastic bag No changes Observations 1. Tell students to follow instructions and to write their observations for each experiment. 2. At the end of each experiment, ask students what they observed. Write the results on the board. 3. Tell the class the reasons for the observations (see chart below) and write reasons on the board for students to copy. 4. Repeat for Experiment 2 in the same test tube. 5. Repeat for Experiment 3 and 4 in the second test tube 6. Repeat for Experiment 5, 6 and 7 in the third test tube Ask students: What chemicals are responsible for the following 1. The bag feels cold(er)? The sodium bicarbonate mixed with water caused the temperature to decrease see Experiment The bag feels warm(er)? The calcium chloride mixed with water caused the temperature to increase see Experiment 3. Your Notes:

10 3. The mixture fizzes, and the bag fills up with gas? Experiment 6 showed that water, calcium chloride, and sodium bicarbonate are all necessary for this reaction, This is the only experiment that produced a gas plus temperature change. Since no other combinations produced the reaction observed in the Ziploc bag, we can conclude that all three reagents must be present. 4. The mixture turns from red to yellow? Phenol red is an indicator which turns red in basic solution and yellow in acidic solution. Nothing started bubbling or changing temperature when the phenol red was added in experiments 2 and 4.. Phenol red is not necessary for the reaction to take place., but it showed that a chemical reaction had taken place in Experiment 6. Explanations for Results of Experiments Reactants Observations Explanation Demonstration by VSVS team H 2 O plus phenol red solution No reaction None Experiment 1 in test tube 1 Experiment 2 in test tube 1 Experiment 3 in test tube 2 Experiment 4 in test tube 2 Experiment 5 in test tube 3 NaHCO 3 plus H 2 O Add a squirt of phenol red to previous test tube CaCl 2 plus H 2 O Add a squirt of phenol red to previous test tube Solid NaHCO 3 plus solid CaCl 2 Solid is slightly soluble; final solution color is cloudy white; the temperature of the solution is colder. Solution color is cloudy pink/red CaCl 2 Ca 2+ (aq) + 2 Cl - (aq) Solid dissolves into solution and forms a cloudy mixture, then clear; the temperature of the solution becomes warmer. Color is red. No reaction The temperature of the solution in the test tube decreases because baking soda absorbs heat when it dissolves in water. This reaction is Endothermic. Baking soda (NaHCO 3 ) is weakly basic (ph of 8.4), so the color of phenol red indicator t does not change Anhydrous calcium chloride gives off heat when it dissolves in water. It is Exothermic. Phenol red does not change color. None Experiment 6 in test tube 3 Experiment 7 in test tube 3 CaCl 2 plus NaHCO 3 plus H 2 O Add a squirt of phenol red to previous test tube Bubbles form; fizzing sound is heard; test tube is cold to touch; solution color is cloudy white. Color changes to yellow The test tube fills with carbon dioxide gas because the hydrogen ion (formed by ionization of bicarbonate) reacts with remaining bicarbonate ion to give carbon dioxide gas. There will be cold and hot spots, and the test tube continues to feel cold because heat is being absorbed. See equation below. CO 2 gas bubbles in water make an acidic solution. Your Notes:

11 Clean-up: The VSVS team should collect all Ziploc bags and used cups and put them in the trash bag. Make sure the Ziploc bags containing the reaction mixture are sealed before you put them in the trash bag. Then put everything else in the kit box along with the trash bag and return it to the VSVS lab. IV. VSVS BACKGROUND INFORMATION ON CHEMICAL EQUATIONS This information is beyond the scope of 7 th graders, and is for VSVSer only. The equations for the reactions that occur when anhydrous calcium chloride is added to the sodium bicarbonate solution are given below. Sodium bicarbonate solid dissolves in water and separates into the 2 different ions: This is a physical change. NaHCO 3 Na + (aq) + HCO 3 (aq) The bicarbonate ion (HCO 3 - ) is a weak acid and partially ionizes in solution. HCO 3 - (aq) H + (aq) + CO 3 2- (aq) When water is added to calcium chloride, the solid dissolves and separates into the 2 different ions: CaCl 2 (s) Ca 2+ (aq) + 2 Cl - (aq) This reaction is exothermic, and is actually a chemical change. Anhydrous calcium chloride rehydrates and makes strong bonds with water. If a solution of calcium chloride and water is allowed to evaporate, the recovered compound is not chemically the same as the initial anhydrous calcium chloride The calcium ion (Ca 2+ ) reacts with the bicarbonate ion (HCO 3 - ) to form insoluble calcium carbonate and hydrogen ion (H + ). Ca 2+ (aq) + HCO 3 - (aq) CaCO 3 (s) + H + (aq) The bag fills with carbon dioxide gas because the hydrogen ion formed in the reaction of calcium ion and bicarbonate reacts with remaining bicarbonate ion to give carbon dioxide gas. This is similar to the reaction that happens when vinegar is added to baking soda. H + (aq) + HCO 3 - (aq) CO 2 (g) + H 2 O (l) The indicator changes color because the carbon dioxide dissolves in water to produce an acidic solution. CO 2 (g) + H 2 O (l) H 2 CO 3 (aq) H + (aq) + HCO 3 - (aq) (4) Reference: Fun With Chemistry, Vol. 1, 2nd ed.; Sarquis M., Sarquis, J., Eds.; Publ ; Institute for Chemical Education, University of Wisconsin: Madison, 1991; pp Adapted by: Dr. Melvin D. Joesten, Department of Chemistry, Vanderbilt University Pat Tellinghuisen, Director of VSVS Answers: Explanations for Results of Experiments Your Notes:

12 Reactants Observations Explanation Demonstration by VSVS team H 2 O plus phenol red solution No reaction None Experiment 1 in test tube 1 Experiment 2 in test tube 1 Experiment 3 in test tube 2 Experiment 4 in test tube 2 Experiment 5 in test tube 3 NaHCO 3 plus H 2 O Add a squirt of phenol red to previous test tube CaCl 2 plus H 2 O Add a squirt of phenol red to previous test tube Solid NaHCO 3 plus solid CaCl 2 NaHCO 3 Na + (aq) + HCO 3 (aq) Solid is slightly soluble; final solution color is cloudy white; solution is colder. Temperature drops about 4 o C Solution color is cloudy pink/red CaCl 2 Ca 2+ (aq) + 2 Cl - (aq) Solid dissolves into solution and forms a cloudy solution. Solution is warmer. Temperature increases by about 5 o C. Color is red. No reaction The temperature of the solution in the test tube decreases because baking soda absorbs heat when it dissolves in water. This reaction is Endothermic. Color is pinkish because the red is mixing with a white cloudy solution Anhydrous calcium chloride gives off heat when it dissolves in water. This reaction is Exothermic. Phenol red does not change color. None Experiment 6 in test tube 3 Experiment 7 in test tube 3 CaCl 2 plus NaHCO 3 plus H 2 O Add a squirt of phenol red to previous test tube Bubbles form; fizzing sound is heard; test tube is cold to touch; solution color is cloudy white. Temperature drops about 4 o C Color is yellow The test tube fills with carbon dioxide gas because the hydrogen ion (formed by ionization of bicarbonate) reacts with remaining bicarbonate ion to give carbon dioxide gas. There will be cold and hot spots, and the test tube continues to feel cold because heat is being absorbed. See equation below. The products of the reaction have formed an acidic solution

13 VANDERBILT STUDENT VOLUNTEERS FOR SCIENCE Diffusion Fall 2018 Goal: To understand diffusion, the process in which there is movement of a substance from an area of high concentration of that substance to an area of low concentration TN Curriculum Alignment: 7.LS1.2 VSVSer Lesson Outline I. Introduction Discuss the motion of molecules using examples such as the smell of cooking from a distance or the smell of perfume in the air when someone wearing perfume walks by. A. Modeling Semi-Permeable Membranes One VSVS member will show students how to use a container with a wire-screen separating rye seeds and bean seeds as a model for a semi-permeable membrane. The rye seeds, representing small molecules, pass through the screen but the bean seeds, representing large molecules, do not pass through the screen. B. Dialysis tubing and Relative Sizes of Molecules Show students the paper models of iodine, glucose, and starch. Discuss the relative sizes and point out that starch is a "polymer molecule made up of hundreds of glucose molecules joined together. II. Testing for Glucose and Starch A. Glucose Test Student use glucose test strips to become familiar with the positive test for glucose. B. Starch Test Students use iodine to test for starch. III. Diffusion of Glucose and Starch A. Glucose Diffusion A VSVS volunteer should distribute the dialysis tubing (containing glucose and starch) in the cup to each pair of students. B. Predicting Which Molecules Will Diffuse While students are waiting, show them the paper models of the molecules again and have the students try to predict which molecules will diffuse through the tubing. C. Testing for Diffusion of Glucose Groups test for glucose after 10 minutes. D. Testing for Diffusion of Starch After a positive test for glucose outside the dialysis tubing has been obtained, students can add ALL the rest of the iodine to the water in the cup. Students should observe a purple/black color form inside the dialysis tubing. IV. Review Summarize the glucose and starch dialysis results for the whole class. As part of this review, show the models of iodine, glucose, and starch to make sure students understand the relationship of molecular size to their ability to diffuse through semi-permeable membranes. LOOK AT THE VIDEO BEFORE YOU GO OUT TO YOUR CLASSROOM USE THE PPT AND VIDEO TO VISUALIZE THE MATERIALS USED IN EACH SECTION.

14 Notes on solutions used: The glucose solution is made to be 30%. The starch solution is made from soluble starch (a handful of starch peanuts in 1 L. water plus 1 tsp cornstarch. The solution mixture inside the dialysis tubing is 80% glucose/20% starch. 1. Before the lesson: In the car ride, read through this quiz together as a team. Make sure each team member has read the lesson and has a fundamental understanding of the material. 1. What is diffusion? 2. What is a semi-permeable membrane, and what is the relationship between molecular size and ability to diffuse through a semi-permeable membrane? 3. Which molecule(s) is/are permeable through the dialysis tubing? Which is/are impermeable? 4. Which molecule is a polymer? 5. How can the presence of glucose be detected? How can the presence of starch be detected? 2. During the Lesson: Here are some Fun Facts for the lesson for VSVS members Diffusion is a passive process, meaning that it occurs spontaneously, without the input of energy. The rate of diffusion is affected by size of molecule, steepness of concentration gradient, and temperature (related to the speed at which the molecules are moving). Examples of diffusion in everyday life: the contents of a teabag diffuse into hot water, helium diffuses out of a balloon causing it to deflate, the smell of warm cookies diffuses throughout a room Water, oxygen, carbon dioxide, and various other essential molecules are constantly diffusing across the membranes of our cells. The diffusion of water is called osmosis. Water molecules move across a membrane trying to achieve equilibrium. Example: a carrot placed overnight in fresh water will swell; a carrot placed in salt water will shrivel. Set-Up VSVS members do this while one member starts Introduction Materials needed for set-up for 16 pairs: 16 6-oz plastic cups 16 pieces of dialysis tubing containing the glucose and starch mixture. 16 plastic plates 32 1oz cups water Count the number of students and remove enough dialysis tubes for each pair. Place the dialysis tubes into individual 6oz cups and place each cup on a plate. Pour enough water into the cup so that the water JUST covers the tubing. Set aside do not give to students until Part III. Take 32 1-oz cups and pour a little water in the bottom of each cup. Save for Section II. Unpacking the Kit what you will need for each part While one team member starts the introduction, another should write the following vocabulary words on the board: diffusion, osmosis, dialysis tubing, glucose, starch, iodine, semi-permeable membrane Refer to vocabulary words throughout the lesson when you encounter them. Your Notes:

15 For Part IA: Introduction. 16 clear plastic containers with wire screen and seeds, 32 Observation Sheets For Part IB: Relative Sizes of Molecules 1 dialysis tube containing glucose and starch 1 set of laminated paper models of iodine, glucose, and starch For Part II: Testing for Glucose and Starch For Part IIA. Glucose Test 16 Instruction Sheets, 16 plastic bags each containing 3 Glucose Test Strips (in a small bag) and 1 Glucose Test Results Chart (laminated), 16 1-oz bottles of 30% glucose, 16 1-oz cups of water, 16 tweezers For Part IIB. Starch Test Above materials plus additional materials: 16 1 oz. cups of water, 16 dropper bottles of iodine (in a protective plastic container), 16 oz containers of starch suspension (shake well) For Part III: Diffusion of Glucose and Starch IIIA Diffusion: 16 pieces of dialysis tubing placed in 6-oz plastic cups, (see set-up) 16 plastic plates, III B: Predicting Which Molecules Will Diffuse Paper models of the molecules from IB For Part IIIC. Testing for Diffusion of Glucose Glucose strips and tweezers from Part IIA Part III D. Testing for Diffusion of Starch Remaining iodine from Part IIB I. Introduction Learning Goals: Students define the term semi-permeable membrane, give realworld examples, and demonstrate how they can be used to separate different-sized molecules Note: Organize the students into pairs Discuss the motion of molecules using examples such as the smell of cooking from a distance or the smell of perfume in the air when someone wearing perfume walks by. o This happens because molecules are in constant motion and gas molecules (perfume, aroma of cooking) mix (diffuse) with the air in the vicinity. A. Modeling Semi-permeable Membranes Materials oz. clear plastic containers with wire screen and seeds 32 Observation Sheets Ask students: What is a semi-permeable membrane? Your Notes:

16 Include the following information in the discussion: o A semi-permeable membrane is a membrane in a cell that allows materials to pass into and out of a cell. o The openings in the membrane are large enough to allow some substances to move in and out of the cell, but are small enough to keep some substances from leaving or entering the cell. Give each student an observation sheet Give each pair one of the 16 oz. clear plastic containers with lids that contains a wire screen in the middle with rye seeds on one side and bean seeds on the other side. Rye and bean seeds are used to represent molecules of two different sizes. The wire grid screen represents a semi-permeable membrane (such as a cell membrane in plants or animals). The holes represent the pores or openings in the membrane. Ask one student to keep the container in view of all group members and shake the plastic container sideways, keeping the lid up and observe what happens. Ask students to explain what happened.. o The students should observe that the rye seeds can pass through the wire screen (both ways) but the bean seeds cannot. o After a few minutes, the levels of seeds will no longer be equal because the side with the bean seeds will have some of the rye seeds as well. B. Dialysis tubing and Relative Sizes of Molecules Materials: 1 dialysis tube containing glucose and starch 1 set of laminated paper models of iodine, glucose, and starch Show students the paper models of the three molecules, and tell them the names of the molecules. Do not discuss anything about these molecules except to tell them that the solutions they are using today contain these molecules. The VSVS instructor should hold up a dialysis tube with glucose and starch so that the class can see it. o Have the students observe that there are no fluids leaking out of the tubing. o Tell the students that the dialysis tubing is similar to a cell membrane, and that the students are going to discover which of the three molecules are small enough the pass through the tubing. Show the students the tubing in the prepared cups and point out the water just covering the tubing. Tell students to look at the diagram on the observation sheet and point out that the dialysis tubing contains starch and glucose molecules. o Starch molecules are represented by large S s and glucose molecules are represented by G s. o Iodine molecules, represented by I 2 s, are shown outside the dialysis tubing because they will be added to the outer solution during the experiment. o Water is H 2 O Water, H 2 O I 2 I 2 I 2 S G S S S G G Your Notes:

17 Tell students that they will work in pairs for the following experiments. II. Testing for Glucose and Starch Learning Goals: Students identify different indicators that can be used to systematically test for the presence of various molecules Materials - distribute to each pair: 1 Instruction Sheet 1 plastic bag containing 3 Glucose Test Strips (in a small bag) and 1 Glucose Test Results Chart (laminated) 1 1-oz bottle of 30% glucose 1 1-oz cup of water 1 tweezer Note: One VSVS volunteer will demonstrate the following procedure and will give the instructions; the other volunteers should monitor pairs to make sure procedures are being followed accurately and to give assistance as needed. Students can refer to the instruction sheet as they are doing the experiments but you will still need to guide them through the procedures. Tell the students that they need to know how to prove which molecules have moved through the membrane. They need to know how to test for glucose and starch. A. Glucose Test Ask students if they know about testing for glucose with glucose strips. o Diabetics use these strips to monitor their glucose levels. Tell the students to place the 1-oz cup of water and the 1-oz glucose bottle on the appropriate circles on the observation sheet. o Take the cap off of the 1-oz glucose bottle. Tell students not to touch the glucose test strip with their fingers - use the tweezers. Dip one end of the test strip into the 1 oz. plastic bottle labeled glucose. Hold the strip above the bottle to remove any excess solution. o Place this strip in the rectangle on the paper (below the 1 oz bottle). Then test the water cup with another glucose test strip, following the same procedure. Wait a few minutes before checking the results. Tell students to compare the color of glucose test strips with the Glucose Results Color Chart, and record the values from the Glucose Results Color Chart on their observation sheets. o Yellow indicates no glucose and shades of green indicate the presence of glucose. The darker the shade of green, the more glucose is present. o Test strips dipped in glucose should be dark green indicating the presence of lots of glucose. o Test strips dipped in water should remain yellow. Use these strips to verify the final test results later in the lesson. Note: The test strip dipped in water should be yellow indicating the absence of glucose. If anyone s strip did turn green, try to determine the reason the strip turned green. This could happen due to contamination if glucose was spilled in the water or if a student touched the pad of the strip after handling the glucose set-up. Tell students to replace cap on 1-oz bottle of glucose. Your Notes:

18 B. Starch Test Distribute the following additional materials to each pair: 1 1 oz. cup to use for testing water 1 dropper bottle of iodine (in a protective plastic container) 1 1 oz container of starch suspension (shake well) Tell students to place the 1-oz cup of water and the 1-oz starch container on the appropriate circles on the observation sheet. They should shake the 1-oz starch container and then remove the cap. Tell students to add one squirt of iodine to both the 1 oz cup containing water and the 1-oz container of starch. Tell students to check for a color change and record the color, if any, on their observation sheet. A dark purple/black color indicates the presence of starch in the starch container. The water cup should be a light orange/yellow or amber color which indicates the presence of iodine only. Then have students put the cap back on the 1-oz starch container. Tell the students they must not disturb the cup and the dialysis tubing. Learning Goals: Students identify different indicators that can be used to systematically test for the presence of various molecules Students identify different indicators that can be used to systematically test for the presence of various molecules III. Diffusion of Glucose and Starch Materials: Distribute the earlier prepared 6 oz. plastic cups containing a piece of dialysis tubing in water for each pair and plates. A. Glucose Diffusion Tell students that diffusion of glucose takes time, but it has already been happening while they have been discussing diffusion. They need to leave the dialysis tubing for another 10 minutes to allow time for diffusion to occur. Go on with section B while students wait. B. Predicting Which Molecules will Diffuse Materials: 1 set of laminated paper models of iodine, glucose, and starch (paper models are stored in binder) Review the relative size of the molecules by showing the students the paper models of the three molecules again. Discuss the relative sizes of the molecules, pointing out that the results of today s activities will be dependent upon the different sizes of iodine, glucose, and starch molecules. Point out that starch is a "polymer molecule made up of hundreds of glucose molecules joined together. Have the students refer back to their seed containers. o Tell the students that this is a good model for a semi-permeable membrane. Your Notes:

19 o The small rye seeds represent small molecules, such as water, iodine, or glucose that can pass through a porous membrane both ways while larger molecules cannot. o The larger bean seeds represent large molecules such as starch molecules that cannot pass through the semi-permeable membrane. Ask the students if they can predict which way the different molecules will move. o The iodine is a small molecule and can move from the water outside the tubing, to inside it. o The starch is a large molecule and cannot get outside the tubing. o The glucose is small and should be able to move from inside the tubing to the water on the outside. Tell students that the molecules of substances have been diffusing in the experiments set up earlier in the lesson and it is time to check on these experiments and investigate what has been happening. Caution students to wait for instructions before they do the experiments. C. Testing for Diffusion of Glucose After the tubing has been in the water for about 10 minutes: Ask students to dip a clean glucose test strip into the water close to the dialysis tubing (it may even touch the tubing) and place the test strip on the appropriate rectangle of the observation sheet. While students are waiting for the results of this test, ask them what the results of the glucose test strip will tell them. o If the test strip remains yellow, then no glucose was able to pass through the dialysis tubing. o If the test strip turns green, then glucose was able to pass through the dialysis tubing. Ask students to check the glucose test strip, compare its color with the Glucose Results Color Chart, and record the value on their observation sheet. The glucose test strip should turn green within 1 minute, indicating the presence of glucose in the water. This shows that glucose molecules have passed through the dialysis tubing. If it did not turn green, test again (close to the tube) after several more minutes have passed Ask students to look at the plastic container of seeds. Ask them if this were a model of the glucose experiment, which seeds represent the glucose molecules. o The small seeds are the glucose molecules because they could travel through the dialysis tubing. Ask students to refer to the diagram on the observation sheet and use arrows to show the direction glucose molecules have moved. D. Testing for Diffusion of Starch Note: This part MUST be done after a positive test for glucose has been obtained. The glucose test strips will not work after iodine has been added to the water. Have students unscrew the lid on the iodine bottles and add all the rest of the iodine to the water in the cup that is holding the dialysis tubing. The solution should be a light orange/yellow or amber color. Note: If a positive test occurs when the iodine is added to the water around the dialysis tubing, the tubing has a leak. If this happens, empty their cup, rinse with water, and place a newly rinsed dialysis tubing in the cup and add iodine again. (Use the extra bottle of iodine that was provided.) If all else fails, have them observe the results of another group. Your Notes:

20 Ask students to observe the solution inside the dialysis tubing and the water surrounding it for a few minutes. o If they observe a color change, they should record it on their observation sheet. o Students should observe a purple/black color inside the dialysis tubing. Ask students what this purple/black color tells them. o The purple/black color indicates that iodine molecules have passed through the dialysis tubing and detected the presence of starch inside the dialysis tubing. Since the outside solution is not purple/black, starch molecules have not passed through the dialysis tubing into the water. Tell students to look at the plastic container of seeds. o Ask them if this were a model of the iodine and starch experiment, which seeds represent the iodine molecules and which represent the starch molecules. o The large seeds are the starch molecules because they could not get out of the dialysis tubing; the small seeds are the iodine molecules because they could travel through the dialysis tubing. Ask students to refer to the diagram on the observation sheet and use arrows to show the direction iodine molecules have moved. IV. Review Learning Goals: Students define the term semi-permeable membrane, give real-world examples, and demonstrate how they can be used to separate different-sized molecules Students identify different indicators that can be used to systematically test for the presence of various molecules Summarize the glucose and starch dialysis results for the whole class. Refer to diagram on observation sheet during review. Glucose gave a positive test in the water surrounding the dialysis tubing. Therefore, glucose molecules traveled through the dialysis tubing. The water in the cup remained yellow (the color of iodine), not the purple color found when starch is present. Therefore, starch molecules did not travel through the dialysis tubing into the water. However, there is a purple-black color inside the tubing. Therefore, iodine molecules traveled into the dialysis tubing and reacted with the starch molecules Show the molecule models of iodine, glucose, and starch to the students again to emphasize the relationship between molecular size and the ability to diffuse through a semi-permeable membrane like dialysis tubing. Collect used dialysis tubing in a large ziploc bag or dispose of them at the school. Return all unused tubing. Pour contents of water in all cups down the drain. Return all cups to lab in plastic garbage bag. Please do not let glucose solutions leak into lesson box that makes for a very sticky mess to clean. Return used 1-oz bottles of glucose and starch and all solution containers to the VSVS lab for re-use. Reference for Part V: J. G. Morse and E. Vitz, A Simple Demonstration Model of Osmosis, J. Chem. Educ., Vol. 76, pp , January, Lesson written by Pat Tellinghuisen, Coordinator of VSVS, Vanderbilt University Dr. Melvin Joesten, Professor Emeritus, Chemistry Department, Vanderbilt University Susan Clendenen, Teacher Consultant, Vanderbilt University We gratefully acknowledge the assistance of Ann Orman and Kay Boone, MNPS teachers. Your Notes:

21 Observation Sheet Name Vocabulary Words: diffusion, osmosis, dialysis tubing, glucose, starch, iodine, semi-permeable membrane GLUCOSE TEST cup with water container with glucose What color is the glucose strip after it is dipped in water? cup with water What color is the glucose strip after it is dipped in glucose solution? STARCH TEST container with starch What color is the water after iodine is added? What color is the starch solution after iodine is added? Predict the Direction of Movement of the Molecules: Remembering what size beans crossed the wire screen, predict which molecules will diffuse in what direction in the experiment. Draw arrows next to a starch (S), glucose (G) and iodine (I 2 ) molecule in the cup diagram below, to show the predicted diffusion direction. DIALYSIS TUBING TESTS I 2 I 2 Water, H 2 O I 2 I 2 G S G S S S G G 10 minutes after dialysis tubing is added to water: What is the color of the glucose strip when it is dipped into the liquid closest to the tubing? 5 minutes after the iodine is added: What is the color of solution inside dialysis tubing Were your predictions for the movement of the molecules correct?

22 Observation Sheet - Answers Name Vocabulary Words: diffusion, osmosis, dialysis tubing, glucose, starch, iodine, semi-permeable membrane GLUCOSE TEST cup with water container with glucose What color is the glucose strip after it is dipped in water? no color cup with water STARCH TEST What color is the glucose strip after it is dipped in glucose solution? green container with starch What color is the water after iodine is added? pale yellow the color of dilute iodine What color is the starch solution after iodine is added? Blue/Black Predict the Direction of Movement of the Molecules: Remembering what size beans crossed the wire screen, predict which molecules will diffuse in what direction in the experiment. Draw arrows next to a starch (S), glucose (G) and iodine (I 2 ) molecule in the cup diagram below, to show the predicted diffusion direction. DIALYSIS TUBING TESTS I 2 I 2 Water, H 2 O I 2 I 2 G S G S S S G G 10 minutes after dialysis tubing is added to water: What is the color of the glucose strip when it is dipped into the liquid closest to the tubing? 5 minutes after the iodine is added: What is the color of solution inside dialysis tubing Were your predictions for the movement of the molecules correct?

23 VANDERBILT STUDENT VOLUNTEERS FOR SCIENCE Evidence of a Chemical Reaction Fall 2018 Goal: To show students evidence of a chemical change. Fits TN standards:7ps1.2, 7PS1.3, 7PS1.4 VSVSer Lesson Outline I. Introduction Question students about the difference between physical and chemical changes. Explain what constitutes evidence of chemical reactions. II. Safety Concerns Discuss safety issues. Demonstrate how students will use the small dispensing bottles and the 24-well culture plate. III. Determining if a Chemical Change has Occurred Tell students to follow the instructions on the instruction sheet. You will still need to guide them through the procedures, making sure they understand the instructions. Discuss results with students after they finish each row. Chemical equations for Rows A, B, C are given. Row A: Chemical Reactions That Give a Precipitate (solid) Students should realize that if the solution turns cloudy, a solid (precipitate) is forming. Row B: Chemical Reactions That Involve a Color Change Formation of complex ions cause color changes Row C: Chemical Reactions That Produce a Gas Students look carefully at the bubbles (CO 2 ) produced in solutions IV. Analyzing Results Emphasize the chemistry of carbonates and bicarbonates. Students predict the reaction between marble and HCl V. Review LOOK AT THE VIDEO BEFORE YOU GO OUT TO YOUR CLASSROOM ( USE THE PPT AND VIDEO TO VISUALIZE THE MATERIALS USED IN EACH SECTION. 1. In the car ride, read through this quiz together as a team. Make sure each team member has read the lesson and has a fundamental understanding of the material. Lesson Quiz 1) What are some basic differences between a physical and chemical change? 2) What are signs of a chemical change? 3) What are the major safety concerns in this lesson for students? 4) What is important about the reaction between a carbonate/bicarbonate and an acid? 5) What is a precipitate? 6) Briefly describe the process students will use to identify the unknown at the end of the lesson 7) If a reaction causes the solution to go from colored to clear, does it count as a color change? 8) In all of the reactions in this lesson for which a gas is given off, what is the gas?

24 2. Use these fun facts during the lesson: Chemical changes constantly occur in living organisms. The human body is made up of proteins that help catalyze complex chemical reactions. The products of a chemical reaction have the same total mass as the reactants (law of conservation of mass). Unpacking the Kit What you will need for each section: VSVSers do this while 1 person is giving the Introduction. Note that students are put into pairs and should have their pencils ready While one team member starts the introduction, another should write the following vocabulary words on the board: physical change, chemical change, chemical reaction, formula, solution, precipitate, compound, mixture For Part III. Determining If a Chemical Change Has Occurred 34 safety goggles for students and VSVS members well culture plates with lids 16 plastic plates Instruction sheets, obs sheets 15 sets of dropper bottles of each: 1.0 M HCl hydrochloric acid 2.5 M Na 2 CO 3 sodium carbonate 0.5 M NaHCO 3 sodium bicarbonate 0.1 M Cu(NO 3 ) 2 copper (II) nitrate 0.1 M Fe(NO 3 ) 3 iron (III) nitrate 0.1 M KSCN potassium thiocyanate A. Demonstration Bag A 2 oz bottle of 0.1 M CaCl 2, 2 oz bottle of 1 M Na 2 CO 3, 2 10 oz clear cups 4 jars containing the products, with precipitate in bottom B. Demonstration Bag B 2 oz bottle of 0.05 M Na 2 S 2 O 3, 2 oz bottle of 0.01 M I 2, 2 10 oz clear cups C. Demonstration Bag C - 2 oz bottle of 1 M HCl, jar of Na 2 CO 3, 1 teaspoon, and 1 10 oz clear cup For Part IV. Analyzing Results 15 small pieces of marble CaCO 3 (in a small bag) For Part V. Optional: Identifying an Unknown 2 sets of 1oz dropper bottles of each of the following unknowns: Unknown A: NaHCO 3 3, Unknown B: CaCl 2, Unknown C: HCl, Unknown D: KSCN, I. Introduction Learning Goals: Students can name the different indicators that a chemical reaction has occurred. Your Notes:

25 Ask students: What is the difference between a physical change and a chemical change? Be sure to include the following information in the discussion: A physical change does not change the chemical properties of a substance. o No new substance is formed during a physical change. o Only the physical properties are changed. o Examples of physical changes include changes in the size, shape, or state of matter. For example, ice, liquid water, and steam. In each of these states, water has physically changed (from solid, liquid, gas) but not chemically. A chemical change does change the chemical properties of a substance. o One or more new substances are formed in a chemical change. o A chemical change cannot be easily reversed. o Examples include: burning paper, digestion of food, bananas browning Ask students: How can you tell when a chemical change has occurred? Some answers may include: a gas given off, color change, precipitation, explosion, burning, etc. Tell students what to look for to determine if a chemical change has occurred: When solutions of two compounds are mixed, it is often possible to determine whether or not a chemical reaction has occurred through visual observation. Evidence of a chemical change might be a color change, a gas given off (it may smell), the formation of a precipitate (a new solid), or an energy (temperature, light) change. Write these observations on the board and share the following explanation with students. 1. A color change occurs when two solutions are mixed and a new color is produced. o BUT, if the color of one solution becomes a paler shade, that change is caused by dilution from the other solution and does not qualify as a color change. 2. Bubbles or fizz indicate that a gas is given off. o BUT, make sure that students understand that the bubbles given off in a soda pop drink is NOT evidence of a chemical change This is just excess gas that is released when the top is opened. Carbonated beverages contain carbon dioxide gas dissolved under pressure, and removing the top lowers the pressure and allows carbon dioxide bubbles to escape. 3. A precipitate forms when two substances react to give a new solid compound that does not dissolve in water. o A precipitate will MOST LIKELY look like a cloudy solution, fine grains in a solution, a swirl, or a fluffy solid. The solution cannot be seen through. Note: When two clear solutions are mixed and a white precipitate forms, this whitish color does not count as a color change. The change should be recorded only as the formation of a precipitate. 4. An energy change (temperature or light) can be either a physical or chemical change. A chemical energy change occurs in a glow stick when chemicals mix to produces light. A physical energy change occurs when you freeze water. Important: Scientists do not rely on just visual observations to determine if a chemical or physical change has occurred. The only real evidence is the formation of new substances with different chemical formulas from the reactants. Your Notes:

26 II. Safety Concerns Tell students they must put on safety goggles before mixing any solutions. Students should not directly smell any chemicals. If anyone gets any of the chemicals on their skin or in their eyes, they should flush immediately with water. Although the solutions are dilute, they could still cause eye damage, especially the 1.0 M HCl. Emphasize to students how important it is for them to follow directions. Organize students in pairs and distribute the following materials to each pair of students: 2 safety goggles 1 24-well culture plate 1 plastic plate 6 dropper bottles of solutions 2 Instruction Sheets 2 Chemical Reactions Observation Sheets VSVS volunteers should put on their safety goggles and keep them on until students are finished mixing chemicals. letters Have students look at the 24-well plate and the instructions at the top of the Chemical Reactions Lab Sheet. Show students how to find the letters A, B, C, D as well as the numbers 1-6 on the 24-well plate. (Letters are imprinted in the plastic along the right side; numbers are imprinted across the top and the bottom. These are tiny and may be difficult to see.) Show students how to match the grid on the lab sheet to the 24-well plate. Tell students to place the 24-well plate on the plastic plate. Give the following instructions to the students: 1. The names and formulas of the compounds being used in this experiment are listed at the bottom of the observation sheet. Have students look at these names and formulas while you pronounce them for the class. The labels on the dropper bottles list both the name and formula. of the compounds. Show students how to be careful when matching the formulas (some of the formulas are very similar). 2. Show students one of the bottles and demonstrate how to get drops out of the bottle. Dropper bottles are easy to use. Apply slow, gentle pressure. Do not remove the red cap from a bottle until it is to be used. Put the cap back on the bottle immediately after use. When using two solutions, put a squirt of the first solution in the correct well so that it is one-fourth full (we do not want students to spend time counting drops). Then add one squirt of the second solution. The well should now be half full. numbers 3. Tell students they will perform the reactions for one row only then stop and discuss the results with the VSVS members. Tell the partners to take turns doing the experiments as they follow the grid on the lab sheet. Both students record their observations on the lab sheet. Students can record NR if No Your Notes:

27 Reaction occurs. Otherwise, they will record color change, gas given off, or precipitate formed. 4. Tell students to follow the instructions on the instruction sheet for mixing solutions. (The instruction sheet lists the same directions as are given below.) III. Determining If a Chemical Change Has Occurred Learning Goals: Students can name the different indicators that a chemical reaction has occurred. Students can identify the specific indicators of a reaction and explain how to look for them One team member should draw a grid of the well plate on the board with all of the rows labeled. Write on this when discussing the results with the students. Note: VSVS volunteers need to monitor the students closely to be sure contamination does not occur. Ensure that students use the correct bottle. Stop and discuss results with students after each row. This is preferable to waiting until students finish all of the experiment since some will finish very quickly and then be bored waiting for others to catch up. The beginning of each reaction is given on the student observation sheet. Students and VSVSers should complete each equation on the board after the reactions in each row are completed. A. Chemical Reactions that Give Precipitates - Row A Demonstration: Show students what a precipitate looks like by doing the following demonstration. Take the demonstration bag marked ROW A. Remove the 2 oz bottles of solutions and the two 10 oz clear cups. Empty each 2 oz bottles into separate cups. Hold the two cups up so the students can see what happens, and then pour one solution into the other. A white solid (precipitate) forms. Point this out as an example of a chemical reaction in which a precipitate forms to the students. Show the students the jars with the clear liquid and precipitate in the bottom. Tell them that these are the products from the same reaction just done, but the products were allowed to stand for several hours. Shake the jar to show the students that the solution will become cloudy again. Your Notes:

28 Note: For each activity DO NOT record the results until the students have completed the experiments for the row since they may wait to copy the answers from the board. Tell students to use the grid on their observation sheet to perform the experiments in Row A. Make sure that they correctly identify the formulas of the compounds being used in a reaction ( listed on the observation sheet). Review and Equations: Ask students what evidence indicated that a chemical reaction occurred. o A precipitate formed in A1 and A2. Put the results on the board. A1: precipitate A2: precipitate Students can look at the equations on the observation sheet: Demo: CaCl 2 + Na 2 CO 3 CaCO NaCl A1: 2 Fe(NO 3 ) Na 2 CO 3 Fe 2 (CO 3 ) NaNO 3 A2: Cu(NO 3 ) 2 + Na 2 CO 3 CuCO NaNO 3 B. Chemical Reactions that Involve a Color Change - Row B Demonstration: Show students what a color change looks like by doing the following demonstration. Take the demonstration bag marked ROW B. Remove the 2 oz bottles of solutions and the two 10oz clear plastic cups. Empty each 2 oz bottles into separate cups. Hold the two clear containers up, and tell students to notice that one is a clear colorless solution and the other is a clear, brown solution. Pour the colorless solution into the brown solution, and ask students to describe what happens. The brown solution turns colorless, but it is still clear (i.e no precipitation). Explain to students that a chemical reaction has taken place because the brown solution turned colorless upon addition of the clear solution. Tell students to use the grid on the lab sheet to perform the experiments in Row B. Background for VSVS Members Only: This is an oxidation-reduction reaction in which iodine is reduced to iodide ion, and thiosulfate ion, S 2 O 4 2-, is oxidized to tetrathionate ion, S 4 O Review and Equations: Ask students what evidence indicated that a chemical reaction occurred. o A color change occurred. Put the results on the board. B1: color change to deep red B2: color change to pale green. Your Notes:

29 Students can look at the equations on their observation sheet. Demo: I Na 2 S 2 O 3 2 NaI + Na 2 S 4 O 6 B1: Fe(NO 3 ) 3 + KSCN Fe(SCN)(NO 3 ) 2 + KNO 3 intense red color B2: Cu(NO 3 ) 2 + KSCN Cu(SCN)(NO 3 ) + KNO 3 pale green color Background for VSVS Members Only: Color changes with metal ion solutions are caused by the formation of complex ions. In the present case, the SCN - (thiocyanate) anion bonds strongly to the Fe 3+ (iron) ion in solution to give an intense deep red color. The SCN - anion also bonds to Cu(II) (copper) ion. C. Chemical Reactions that Produce a Gas - Row C Note: Tell students they will have to look very closely and quickly as soon as they add the second solution to the first solution. The bubbles of gas are small and come off as soon as the solutions are mixed. Demonstration: Show students what a chemical change that produces a gas looks like by performing the demonstration first. Take the demonstration bag marked ROW C. Hold the cup up and ask students to watch very carefully what happens. Put 1 tsp of the solid (Na 2 CO 3 ) into the cup and empty the 2oz bottle (HCl) into it. Ask students to describe what happens. A bubbling up (slight foaming) which quickly subsides indicates a gas is given off. Tell students to watch very carefully for bubbles of gas when they are doing Row C because they may be difficult to see. Tell students to use the grid on the lab sheet to perform all the experiments in Row C. Review and Equations: Ask students what evidence indicated that a chemical reaction occurred. o Bubbles/gas was given off. Put the results on the board. C1: bubbles/gas C2: bubbles/gas Students can look at the equations on the observation sheet. Demo: Na 2 CO 3 + 2HCl 2NaCl + CO 2 + H 2 O C1: NaHCO 3 + HCl NaCl + CO 2 (g) + H 2 O C2: Na 2 CO 3 + 2HCl 2NaCl + CO 2 (g) + H 2 O Your Notes:

30 IV. Analyzing Results Learning Goals: Students can analyze compounds reactions with one another and use that data to identify an unknown compound. Carbonates: Write CO 3 on the board and tell students that formulas that include CO 3 as part of the formula are called carbonates. One form of carbonate, sodium carbonate is commonly referred to as "washing soda." It is part of many laundry detergents and dish washing detergents. Tell students to look at the ingredients of the copy of a washing soda box on their Instruction sheet. Sodium carbonate is listed as an ingredient. Bicarbonates: Write HCO 3 on the board and tell students that formulas that include HCO 3 as part of the formula are called bicarbonates. A common source of bicarbonate is baking soda, whose scientific name is sodium bicarbonate. Sodium bicarbonate is used for baking and as a deodorizer. Tell students to look at the ingredient label on baking soda and notice it says sodium bicarbonate. Reactions of Carbonates and Bicarbonates: Ask students to look at each box in row C and circle the formulas that have CO 3 or HCO 3 as part of the formula.. Write HCl on the board. o Tell students that HCl is an acid called hydrochloric acid. o Tell students to put boxes around all the HCl s in Row C Ask students what happened in row C when an acid was added to a carbonate or bicarbonate. o o A gas was given off. Ask students if they have ever made a volcano at home or at school. Ask students if they remembered what they added to make the lava. Most likely, they used vinegar and baking soda. Vinegar is an acid, and when added to baking soda (sodium bicarbonate), it bubbles as it releases a gas. Ask students what happens when you add an acid to carbonate or bicarbonate. When an acid is added to a carbonate or bicarbonate a chemical reaction occurs. This is evidenced by the fact that a gas is given off. Tell students that the gas given off in these reactions is carbon dioxide. Identifying Carbonates Using Chemical Reactions: Tell students that chalk, limestone and marble are all calcium carbonate. If the formula for calcium carbonate is CaCO 3, what might happen if an acid (HCl) is added to marble? It will bubble (give off a gas). Write the first half of the equation, CaCO 3 (s) + HCl (aq)...on the board, and ask students to hypothesize what will happen, and what the products will be. The gas will be CO 2. Your Notes:

31 The full equation is: CaCO 3 + 2HCl CaCl 2 + CO 2 + H 2 O Have VSVS members hand out a piece of marble to each pair of students. Tell students that they are going to test their hypothesis to see if the marble will bubble when HCl is added. Have students add the marble to C5 and to squirt some HCl into the well. Ask students what happened. Was their hypothesis correct? Yes, it should bubble when HCl is added. Tell students that many statues are made of limestone and marble. Ask students what they think happens to statues when acid rain falls on them. The carbonate in the statue reacts with acid liberating a gas and causing the statue to decompose. Background Information (in case students ask about acid rain): Acid rain is caused by the presence of varying amounts of sulfuric acid and nitric acid in rain drops. Fossil fuels, particularly coal and oil, contain sulfur as an impurity. When fossil fuels are burned, the sulfur combines with oxygen to form sulfur oxides that are gases released into the air. When it rains, the water reacts with these gases to form sulfuric acid. When vehicles burn gasoline or diesel fuel, nitrogen oxides are emitted into the air, and these react with water to produce nitric acid. The amount of sulfuric acid and nitric acid in acid rain depends on the location. The acid rain in Nashville is primarily caused by nitric acid from the high density of vehicles, while the acidity of rain in industrialized areas will be caused by the presence of both sulfuric and nitric acids. As a result of the Clean Air Act, industrial and power plants are emitting much lower amounts of sulfur oxides; however, the emission of nitric oxides from vehicle exhausts is still a problem. V. Optional: Identifying an Unknown Tell students they will be given a colorless solution that contains one of the following compounds dissolved in water Unknown A: NaHCO 3 Unknown B: CaCl 2 Unknown C: HCl Unknown D: KSCN These are the same colorless solutions that they have been doing the experiments with, except that CaCl 2 was used only in Demonstration A. Tell them that they will follow a plan, using the dropper bottles from the chemical reaction kit, to determine the identity of the unknown. Students can work in pairs, groups, or as a class. Distribute the 8 unknown dropper bottles throughout the class, so that pairs or groups of students have access to one unknown. Tell students to: 1. Follow the plan in Row D and add a squirt of their unknown to the 6 wells in Row D of the well plate. 2. Add a few drops from their known dropper bottles, one well at a time. 3. Write down the observation immediately after each addition. 4. Look at the results in Rows A, B and C, including the demonstration reactions, to determine what the possible reactions are. Your Notes:

32 Ask students: What do you think your unknown is? What is your proof for what you ve listed in (a)? The proof should be stated something like the answer response in the plans given above but specific for the unknown. For example, if the unknown was CaCl 2, the proof statement could be: A precipitate formed when Na 2 CO 3 solution was added. The CaCl 2 solution is the only one of the possible unknowns that will give a precipitate with Na 2 CO 3. Write balanced chemical equations for the reactions you used to determine the identity of the unknown. (Refer to equations in lesson (Section VIII)) Optional: Answer these questions after finishing the chemical reactions observation sheet. 1. Write complete, balanced equations for the following: a. One reaction in Row A that gave a precipitate. Refer to equations in lesson (Section VIII) b. One reaction in Row B that gave a color change. Refer to equations in lesson (Section VIII) c. One reaction in Row C that gave a gas. Refer to equations in lesson (Section VIII) VI. Review Questions Ask students: What is a physical change? What is a chemical change? What are the chemical changes we saw today? How do we know when a chemical change has occurred? (answer on p. 3) VII. Clean-up Have students put the dropper bottles back in the Ziploc bag. Make sure that the bottles are all upright. Leaks make for nasty clean-up tasks. Collect the Ziploc bags and the goggles. Place the lids on the 24-well plates and carefully put them in the Rubbermaid container. Place the lid on the Rubbermaid container and put it in the bottom of the box. (If you can rinse them out at the school, do so, PLEASE) Place the ziploc bags and other materials in the box. Collect all instruction sheets in sheet protectors and put them in the box. Lesson written by Dr. Melvin Joesten, Chemistry Department, Vanderbilt University Pat Tellinghuisen, Coordinator of VSVS, Vanderbilt University Your Notes:

33 NAME Class Activity Sheet Extension Activity 1. You will be given an unknown colorless solution that contains one of the following compounds dissolved in water: CaCl 2, KSCN, HCl, NaHCO 3. Follow Row D to determine the identity of your unknown. a. What do you think your unknown is? If there is more than one possibility, list both. b. What is your proof for what you ve listed in (a)? c. Write balanced chemical equations for the reactions you used to determine the identity of the unknown. 1. Write complete, balanced equations for the following (choose a correct equation from the list below): a. One reaction in Row A that gave a precipitate. b. One reaction in Row B that gave a color change. c. One reaction in Row C that gave a gas. Chemical Equations for Chemical Reactions in this Lesson Abbreviations: s = solid, aq = aqueous, g = gas, l = liquid CaCl 2 (aq) + Na 2CO 3 (aq) CaCO 3 (s) + 2 NaCl (aq) 2 Fe(NO 3) 3 (aq) + 3 Na 2CO 3 (aq) Fe 2(CO 3) 3 (s) + 6 NaNO 3 (aq) Cu(NO 3) 2 (aq) + Na 2CO 3 (aq) CuCO 3 (s) + 2 NaNO 3 (aq) I 2(aq) + 2 Na 2S2O 3(aq) 2 NaI(aq) + Na 2S 4O 6 (aq) Fe(NO 3) 3 (aq) + KSCN (aq) Fe(SCN)(NO 3) 2 (aq) + KNO 3 (aq) Cu(NO 3) 2 (aq) + KSCN (aq) Cu(SCN)(NO 3) (aq) + KNO 3 (aq) Na 2CO 3 (s) + 2HCl (aq) 2NaCl (aq) + CO 2 (g) + H 2O (l) NaHCO 3 (aq) + HCl (aq) NaCl (aq) + CO 2 (g) + H 2O (l) Na 2CO 3 (aq) + 2HCl (aq) 2NaCl (aq) + CO 2 (g) + H 2O (l) CaCO 3 (s) + 2HCl (aq) CaCl 2 (aq) + CO 2 (g) + H 2O (l) Your Notes:

34 Class Activity Sheet ANSWER SHEET Answer these questions after finishing the chemical reactions observation sheet. 2. Write complete, balanced equations for the following: a. One reaction in Row A that gave a precipitate. Refer to equations on worksheet One reaction in Row B that gave a color change. Refer to equations on worksheet One reaction in Row C that gave a gas. Refer to equations in lesson (Section VIII) You will be given an unknown colorless solution that contains one of the following compounds dissolved in water: CaCl 2, KSCN, HCl, NaHCO 3. Follow Row D to determine the identity of your unknown. What do you think your unknown is? 5. What is your proof for what you ve listed in (a)? The proof should be stated something like the answer response in the plans given above, but specific for the unknown. For example, if the unknown was CaCl 2, the proof statement could be: A precipate formed when NaHCO 3 solution was added. The CaCl 2 solution is the only one of the possible unknowns that will give a precipitate with NaHCO Write balanced chemical equations for the reactions you used to determine the identity of the unknown. Refer to equations below Your Notes:

35 Chemical Reactions Observation Sheet Name Vocabulary Words: physical change, chemical change, chemical reaction, formula, solution, precipitate, compound, mixture In each box, use the following choices to record your observations: color change, precipitate formed, gas given off, NR (no reaction) Add other observations if you wish. Ex: lots of bubbles, fizz, small or large bubbles, cloudy precipitate. A1 Fe(NO 3 ) 3 + Na 2 CO 3 A2 Cu(NO 3 ) 2 + Na 2 CO 3 A3 A4 A5 A6 Demonstration CaCl 2 + Na 2 CO 3 CaCl 2 + Na 2 CO 3 CaCO 3 + 2NaCl 2 Fe(NO 3 ) Na 2 CO 3 Fe 2 (CO 3 ) NaNO 3 Cu(NO 3 ) 2 + Na 2 CO 3 CuCO NaNO 3 B1 Fe(NO 3 ) 3 +KSCN B2 Cu(NO 3 ) 2 +KSCN B3 B4 B5 B6 Demonstration I 2 + 2Na 2 S2O 3 I Na 2 S 2 O 3 2 NaI + Na 2 S 4 O 6 Fe(NO 3 ) 3 + KSCN Fe(SCN)(NO 3 ) 2 + KNO 3 Cu(NO 3 ) 2 + KSCN (aq) Cu(SCN)(NO 3 ) + KNO 3 C1 NaHCO 3 + HCl C2 Na 2 CO 3 + HCl C3 C4 C5 marble solid CaCO 3 + HCl C6 Demonstration Na 2 CO 3 + 2HCl Na 2 CO 3 + 2HCl 2NaCl + CO 2 + H 2 O NaHCO 3 + HCl NaCl + CO 2 + H 2 O Na 2 CO 3 + 2HCl 2NaCl + CO 2 + H 2 O CaCO 3 + 2HCl CaCl 2 + CO 2 + H 2 O D1 NaHCO 3 + unknown D2 KSCN + unknown D3 Fe(NO 3 ) 3 + unknown D4 Cu(NO 3 ) 2 + unknown D5 HCl + unknown D6 HCl - hydrochloric acid Na 2 CO 3 - sodium carbonate NaHCO 3 - sodium bicarbonate Cu(NO 3 ) 2 - copper (II) nitrate Fe(NO 3 ) 3 - iron (III) nitrate KSCN - potassium thiocyanate CaCl 2 - calcium chloride

36 A1 Fe(NO 3 ) 3 + Na 2 CO 3 precipitate A2 Cu(NO 3 ) 2 + Na 2 CO 3 precipitate Chemical Reactions Lab Sheet Answer Key A3 A4 A5 A6 Demonstration CaCl 2 + Na 2 CO 3 white precipitate B1 Fe(NO 3 ) 3 +KSCN color changedeep red B2 Cu(NO 3 ) 2 +KSCN color change - pale green color B3 B4 B5 B6 Demonstration I Na 2 S2O 3 color change brown to colorless C1 baking soda NaHCO 3 + HCl gas given off C2 washing soda Na 2 CO 3 + HCl gas given off C3 C4 C5 marble solid CaCO 3 + HCl gas given off C6 Demonstration Na 2 CO 3 + 2HCl gas given off D1 baking soda NaHCO 3 + unknown D2 potassium thiocyanate KSCN + unknown D3 iron nitrate Fe(NO 3 ) 3 + unknown D4 copper nitrate Cu(NO 3 ) 2 + unknown D5 hydrochloric acid HCl + unknown D6 HCl - hydrochloric acid Na 2 CO 3 - sodium carbonate NaHCO 3 - sodium bicarbonate Cu(NO 3 ) 2 - copper (II) nitrate Fe(NO 3 ) 3 - iron (III) nitrate KSCN - potassium thiocyanate CaCl 2 - calcium chloride

37 Answer Sheet for Unknown Solutions baking soda NaHCO 3 + unknown A (Na 2 CO 3 ) potassium thiocyanate KSCN+ unknown A (Na 2 CO 3 ) iron nitrate Fe(NO 3 ) 3 + unknown A (Na 2 CO 3 ) copper nitrate Cu(NO 3 ) 2 + unknown A (Na 2 CO 3 ) hydrochloric acid HCl + unknown A (Na 2 CO 3 ) NR NR PPT PPT Gas given off baking soda NaHCO 3 + unknown B ( CaCl 2 ) potassium thiocyanate KSCN+ unknown B ( CaCl 2 ) iron nitrate Fe(NO 3 ) 3 + unknown B ( CaCl 2 ) copper nitrate Cu(NO 3 ) 2 + unknown B ( CaCl 2 ) hydrochloric acid HCl + unknown B ( CaCl 2 ) PPT baking soda NaHCO 3 + unknown C (HCl) NR potassium thiocyanate KSCN + unknown C (HCl) NR iron nitrate Fe(NO 3 ) 3 + unknown C (HCl) NR copper nitrate Cu(NO 3 ) 2 + unknown C (HCl) NR hydrochloric acid HCl + unknown C (HCl) Gas given off baking soda NaHCO 3 + unknown D (KSCN) NR potassium thiocyanate KSCN + unknown D (KSCN) Color change iron nitrate Fe(NO 3 ) 3 + unknown D (KSCN) Color change copper nitrate Cu(NO 3 ) 2 + unknown D (KSCN) NR hydrochloric acid HCl + unknown D (KSCN) NR baking soda NaHCO 3 + unknown E ( NaHCO 3 ) NR potassium thiocyanate KSCN + unknown E ( NaHCO 3 ) Color change iron nitrate Fe(NO 3 ) 3 + unknown E ( NaHCO 3 ) Color change copper nitrate Cu(NO 3 ) 2 + unknown E ( NaHCO 3 ) NR hydrochloric acid HCl + unknown E ( NaHCO 3 ) NR NR PPT PPT Gas given off

38

39 VANDERBILT STUDENT VOLUNTEERS FOR SCIENCE Investigating Ionic, Covalent and Metallic Bonding Fall 2018 Acknowledgement: We want to thank NASA and the Tennessee Space Consortium for funds to purchase the Elenco Snap Circuit kits. Goal: To measure the conductivity of solids and solutions using an LED in a circuit. TN Curriculum Alignment: 7.PS1.5, 7.PS1.2 VSVSer Lesson Outline I. Introduction to Bonding in Ionic, Molecular and Metallic Compounds. Students are introduced to ionic, molecular and metallic compounds Explain Static and Current electricity. Write the vocabulary words on the board and explain conductors and nonconductors. II. Explaining the Circuit Demonstration Explain the circuit and LED and demonstrate how the students will use the red and black lead wires to test conductivity. Students discover that an electrical current will flow through a metal nail (which has metallic bonding) but not through a plastic cap. III. Conductivity of Solutions of Ionic and Molecular Compounds Explain that some solutions conduct an electrical current. Students will test a number of solutions. Make sure they understand the importance of rinsing off the metal leads of the red and black wires in distilled water between each conductivity test. IV. Using a Polymer to Distinguish Between Ionic and Molecular Compounds Students add ionic or molecular compounds to a gel of sodium polyacrylate and observe results. a. Testing ionic and molecular compounds V. Review Review the results of the lesson and the vocabulary words. Materials 1 ea Models of NaCl and water compounds 1 plastic bag containing a n assembled grid and nail and plastic bottle cap 16 sets of grids with assembled circuit 16 sets of instruction sheets 32 observation sheets 64 jars containing: salt, sodium bicarbonate, sugar and glucose 80 2oz cups 16 bags containing 4 taster spoons,1 chemwipe tissue, 4 toothpicks ml bottles distilled water oz cups oz cups (the opaque ones) 2 containers sodium Polyacrylate 4 teaspoons 1 1L container of distilled water 16 Plates 16 6-well plates

40 1. In the car ride, read through this quiz together as a team. Make sure each team member has read the lesson and has a fundamental understanding of the material. Lesson Quiz 1. What is the difference between static electricity and current electricity? 2. How can you tell the difference between a good conductor and a poor conductor through a conductivity test? 3. Will an ionic compound or a molecular compound conduct electricity when dissolved in water? Why? 4. Is sugar solution a conductor? Why? 5. At the conclusion of the lesson should the leads be snapped together before they are placed back in the kit? (NO) Do not hand out materials until you have discussed the following background information. Unpacking the Kit What you will need for each section: For Part I. Introduction While one person is giving the Introduction, another VSVS member writes the following vocabulary words on the board: ionic compounds, ionic bonds, molecular compounds, covalent bonds, conductors, insulators. Other VSVSers count the number of students in the class and put 1 tsp sodium polyacrylate into a 12 oz cup (the opaque one) and 200mL water into 10 oz cups For Part II. Explaining the Circuit Demonstration 1 grid with assembled circuit, plus a bag with a nail and a bottle cap for demonstrating conductivity. For Part III. Conductivity of Solutions Materials for each pair: 1 grids with assembled circuit, 1 instruction sheets, 2 observation sheets 4 jars containing: salt, sodium bicarbonate, sugar and glucose,5 2oz cups, 1 bag containing 4 tasterspoons,1 chemwipe tissue, 4 toothpicks, water bottle, For Part IV. Using a Polymer to Distinguish Between Ionic and Molecular Compounds Materials for each pair: 1 10 oz cup containing 1tsp sodium Polyacrylate, 1 10 oz cup containing 200 ml water, 1 teaspoon 1 Plate, 1 6-well plates 4 jars containing: salt, sodium bicarbonate, sugar and glucose5 2oz cups, 1 bag containing 4 tasterspoons,1 chemwipe tissue, 4 toothpicks from Part III For Part V. Experiment - Investigating the Effect of Adding Ionic and Molecular Compounds to Sodium Polyacrylate 1. Introduction to Bonding in Ionic and Molecular Compounds and Metals Materials: Models of ionic NaCl, and molecular water H 2 O While one person is giving the Introduction, another VSVS member writes the following vocabulary words on the board: ionic compounds, ionic bonds, molecular compounds, covalent bonds, conductors, insulators. Note: This section is meant to be a refresher of material they have already learned in class. It is more important that you get to the experimental parts. Ask students: What are the different types of bonding that can form between atoms? Answer: ionic, covalent or metallic

41 1. Ionic Compounds: Show students the model of sodium chloride and explain that the sodium chloride crystal has a repeating pattern of equal numbers of Na + and Cl - ions in 3 dimensions. This is called a crystal lattice. An ionic compound forms between positive and negative ions that are created when atoms either lose or gain electrons. Some ions are formed from single atoms, such as the sodium and chloride ions in salt (sodium chloride). Some ions are made of more than one atom, such as the bicarbonate ion (HCO 3 - ) in sodium bicarbonate (NaHCO 3 ). 2. Molecular Compounds: Show students the plastic bag containing the water molecules. The hydrogen and oxygen molecules are covalently bonded. A molecular compound is made up of atoms that are covalently bonded. Covalent bonds are formed when atoms share electrons. 3. Metals easily lose valence electrons and become metal ions. a. Metallic bonds, like covalent bonds, also involve sharing electrons. b. But in metals, the electrons are shared over millions of atoms, while in molecular compounds, the electrons are shared between just 2 or 3 atoms. c. For example, in a covalently bonded compound like oxygen (O 2 ), electrons are shared between the 2 oxygen atoms; however, in a metallically bonded compound like a gold bar, electrons are shared over all gold atoms in that bar. You might hear metallic bonding referred to as a sea of electrons for this reason. One of the differences in properties between ionic and covalent compounds is the ability to conduct an electrical current when they are added to water. Most metals, unlike either ionic or covalent compounds, conduct electricity as solids and don t need to be dissolved in water. Tell students that they are going to conduct an experiment to determine if a compound is ionic or covalent. Why is the science in this lesson important? In the food service/production industry, cooking equipment may be sanitized with harsh chemicals that have high concentrations of ions. A conductivity test can be used to determine if the cleaning agent has been sufficiently rinsed away. If there is still significant conductivity when pure water is in contact with the equipment, then the equipment should be further rinsed to remove the cleaning agent. Public water facilities often monitor the conductivity of their output water to determine how much material is dissolved in the water (total dissolved solids). It is important to note that this test only accounts for the dissolved solids that are conductive. However, this method would be useful to determine if water has been demineralized, that is, if hard water has been effectively treated to remove some of the contaminating ions. As another example, conductivity tests can be used to determine if desalination processes have removed all of the salt from ocean water so that it becomes fit for human consumption.

42 II. Explaining the Circuit Learning Goals: Students define static and current electricity and observe that metallic compounds conduct electricity and molecular compounds do not. Materials 1 grid with assembled circuit, plus a bag with a nail and a plastic bottle cap for demonstrating conductivity. Ask students if they know what the 2 types of electricity are. 1. Static electricity is the build-up of electrical charge. It does not flow. Lightning is an example of static electricity being discharged after having been built up. 2. Current electricity is moving electrical charge, usually electrons. Some materials have more free electrons than others. Current electricity flows through a completed circuit. Demonstration Materials per pair 1 set of grids with assembled circuit 1 set of instruction sheets 2 observation sheets Learning Goals: Students learn what an LED is, and understand how it is used to show that a circuit is complete. VSVS team members should hold up the demonstration circuit to show the students. Tell the students to look at Diagram 1and their circuit board. Point out the different parts batteries, circuit connectors, black and red leads, resistor and LED light. Point out that a lead is a wire wrapped in an insulator. Explain LED s to the students: LED s (Light Emitting Diodes) are more sensitive than light bulbs and glow brightly with small currents. Diagram 1 VSVS information only: LED s are made from semiconductors. They can be damaged by high currents and so are used with resistors to limit the current. Do NOT allow the students to remove the resistor. Ask the students what you should do to make the LED glow. Touch the black and red lead together to complete the circuit. Show the students that this is correct and that the LED emits light. Tell the students that the circuit is closed when the red and black leads are touching. Electrical current can flow through LEDs in one direction only. Show the students the direction of flow. Current flows from the positive end ( knob ) of the battery to the negative ( flat ) end. Tell the students that electricity flows through some materials better than others. Conductors are materials that allow the movement of electrons through them. Metals have many free electrons that can easily move, and therefore are good conductors. Free

43 electrons are those not strongly held by the atom s nucleus. Since they are not strongly held, they are able to jump from one atom to another. Now touch the end of one lead wire to the head of the nail and the end of the other lead to the point of the nail. The LED again lights up indicating that the circuit is closed. The metal nail is a good conductor of electricity and completes the circuit. Remember that metallic bonding involves a sea of electrons that allows electrical currents to flow. Repeat with the bottle cap, putting the ends of the leads on opposite sides of the bottle cap. The LED will not light up, indicating the plastic bottle cap is not a conductor. Plastic bottle tops are made from molecular compounds, which have covalent bonds. III. Conductivity of Solutions of Ionic and Molecular Learning Goals: Students understand that solutions of ionic solutions conduct electricity and solutions of molecular compounds do not. compounds Materials per pair 16 sets of grids with assembled circuit 16 sets of instruction sheets 32 observation sheets 16 sets of jars containing: salt, sodium bicarbonate, sugar and glucose solids 80 2oz cups 16 bags containing 4 taster spoons,1 chemwipe tissue, 4 toothpicks ml water bottles (containing distilled water) Background information for VSVS members only (electrolytes and non-electrolytes are not in the 7 th grade vocabulary): Conducting liquids are called electrolytes. An electrolyte contains electrically charged ions that can conduct electricity. Some examples of electrolytic solutions are acids and bases and salt solutions such as sodium chloride (table salt) in water. A non-electrolyte does not allow the flow of electric current because it does not have electrically charged ions that can conduct electricity. Some examples of non-electrolytic solutions are distilled water, sugar water. Electrolytes are important to humans because they are necessary for proper cellular function, muscle function, and neurological function. A greater level of electrolytes is needed during strenuous muscular activity because more electrolytes are lost due to increased sweating. This is the reason why Gatorade and other sports drinks advertise that they replenish electrolytes. Hand out the jars of solids to each group. Tell the students to follow the instruction sheet and to record their results. Tell students to: Rinse the metal ends of the black and red lead wires by dipping them into the cup of distilled water. Tell the students they will need to do this in between each test, to avoid contaminating the next test sample with the one just tested (make sure that the students know what contamination means).

44 Place the 5 2oz cups containing distilled water on top of the diagram on the instruction sheet. Place the corresponding jar of solid next to the cup. Make sure that the students have the order correct. Students must remove only ONE lid at a time, and replace it after pairs have tested the liquid. Students MUST test the solutions in the order given, 1-5 o The non-conducting solutions are tested first, followed by conducting solutions. This will help avoid contamination of the solutions. 1. Testing distilled water: Put the metal ends of both lead wires in the cup containing distilled water, as far apart as possible, and note if the LED is glowing. (It should not). Remove the leads. 2. Testing water plus sucrose (sugar): Remove the lid of the 1 st jar (sugar) and add 1 mini spoon to the water. Stir with a toothpick, and then snap the toothpick in half so it cannot be used again. Repeat the conductivity test. Record your results. Replace the lid on the jar. The LED should not glow. Rinse the metal ends of the wires in the distilled water jar.. 3. Testing water plus glucose: Remove the lid of the 2 nd jar (glucose). Repeat the conductivity test. Record your results. Replace the lid. The LED should not glow. Rinse the metal ends of the wires in the rinse cup. 4. Testing water plus sodium chloride (salt): Remove the lid of jar 3 (salt). Repeat the conductivity test Replace the lid. Record your results. The LED should glow. Rinse the metal ends of the wires in the rinse cup. 5. Testing water plus sodium bicarbonate (baking soda): Remove the lid of the 4 th jar and repeat the conductivity test. Replace the lid. The LED should glow. Record your results. Rinse the metal ends of the wires in the rinse cup Ask students if they can explain the results. 1. Distilled water does not contain ions and thus does not conduct electrical currents. Distilled water is a molecular compound with covalent bonds. (Note that TAP water can conduct an electrical current because it can contain metal salts that are ionic.) 2. Sugar molecules and glucose molecules are molecular compounds that do not split up into ions in water, and so do not conduct electrical currents 3. Solid salt and solid sodium bicarbonate will not conduct electricity because the sodium, chloride and bicarbonate ions are not free to move around in the solid form. However, when they are dissolved in water, the units dissociate completely into ions, and so are conductors of an electric current. IV. Experiment: Using a Polymer to Determine if a Compound is Ionic or Molecular. Materials: oz cups containing 1tsp sodium Polyacrylate oz cups containing 200 ml water 2 containers sodium Polyacrylate 16 teaspoons 16 Plates

45 16 6-well plates 16 1oz jar of sugar, 1oz jar of glucose, 1oz jar of sodium chloride (salt), 1oz jar of sodium bicarbonate (baking soda), 16 bags containing 4 taster spoons, 1 chemwipe tissue, 4 toothpicks Sodium Polyacrylate is a superabsorbent polymer found in disposable diapers and moisture absorbent for automobile and jet fuels. A superabsorbent polymer can absorb and retain extremely large amounts of liquid relative to its own mass] This polymer absorbs about 300 times its weight of tap water (800 times its weight of distilled water because the ions in tap water reduce the absorbing properties of the polymer). Note for VSVS members only: It is a polymer that consists of repeating units of the monomer. The picture is a single unit. It is able to absorb large amounts of water because the sodium ions (Na + ) that are attached to it are replaced by water. Point to the diagrams of sodium polyacrylate on their handout. Point out the Na + ions that are replaced by water molecules Making a gel with sodium polyacrylate. Give each pair a (10 oz) cup containing the sodium polyacrylate and a 10 oz cup containing 200 ml tap water. Tell them to: 1. Pour the water into the cup with the sodium polyacrylate and stir with a spoon. Observe that all the water is absorbed (forms a gel) immediately. VSVS Information only: Sodium polyacrylate will continue to absorb water until there is an equal concentration of water inside and outside the polymer. Each sodium polyacrylate molecule is able to attract and hold thousands of water molecules. Sodium polyacrylate, uses osmosis to soak up water. Because there is a higher concentration of water outside the sodium polyacrylate, it draws in the water through osmosis. Each sodium polyacrylate molecule is able to attract and hold thousands of water molecules.