Introduction Unit Framework Title Exploring Change Unit Framework Annotation

Transcription

1 Title: Exploring Change Subject: Chemistry Topics: Atomic structure, bonding, properties of matter, conservation of matter, chemical formulas, stoichiometry, acids and bases Grade: High School Designers: Laura Kornagay, Bobby Timms, Miriam Jordan, Cheryl Thomasson Introduction Unit Framework Title Exploring Change Unit Framework Annotation This unit is designed to build the enduring understanding that atomic structure dictates bonding, which in turn determines the structure of molecular and ionic compounds, diatomic elements, and allotropes, and that these structures determine the compounds properties. The unit builds on bonding and conservation of mass to begin the study of patterns of reactions, balancing chemical equations and stoichiometric calculations related to the reactions. Both manipulatives and traditional lab activities are integral parts of the exploration in this unit. This unit integrates the understandings from Finding Order and Finding Patterns to explore how atoms and ions bond and the changes that occur when bonds are broken or formed. IUPAC conventions for writing formulas and naming compounds are taught. The mole concept is extended to compounds and balanced equations in this unit. Stoichiometry is introduced and used to make calculations consistent with the conservation of matter. Acids and bases are explored as specific categories of compounds. The instruction, tasks, and assessments in this unit are suggested but should be adjusted, omitted, or enhanced as needed for specific class situations. Some classes may need more time, practice, or instruction for some concepts. Others may need less. Fore these reasons, the number of days required may need adjustment. Approximate Duration for the Unit Framework 5 weeks-variable (Depending on the needs of the students, the actual time needed for practice, informal assessment, and adjusting instruction may be more than 5 weeks.) Authors Laura Kornagay, Bobby Timms, Miriam Jordan, Cheryl Thomasson Address Standards Focus Content Standards SC1. Students will analyze the nature of matter and its classifications. SC1b. Identify substances based on chemical and physical properties. SC1c. Predict formulas for stable ionic compounds (binary and tertiary) based on balance of charges. SC1d. Use IUPAC nomenclature for both chemical names and formulas: Ionic compounds (Binary and tertiary) Covalent compounds (Binary and tertiary) Acidic compounds (Binary and tertiary) SC2. Students will relate how the Law of Conservation of Matter is used to determine chemical 1

2 composition in compounds and chemical reactions. SC2a Identify and balance the following types of chemical equations: Synthesis Decomposition Single Replacement Double Replacement Combustion SC2b. Experimentally determine indicators of a chemical reaction: specifically precipitation, gas evolution, water production, and changes in energy to the system. SC2c. Apply concepts of the mole and Avogadro s number to conceptualize and calculate Empirical/molecular formulas, Mass, moles and molecules relationships SC2d. Identify and solve different types of stoichiometry problems, specifically relating mass to moles and mass to mass. SC3. Students will use the modern atomic theory to explain the characteristics of atoms. SC3e. Compare and contrast types of chemical bonds (i.e. ionic, covalent). SC7. Students will characterize the properties that describe solutions and the nature of acids and bases. SC7b. Compare, contrast, and evaluate the nature of acids and bases: Integrated Characteristics of Science Standards SCSh1a Exhibit curiosity, honesty, openness, and skepticism in their own scientific activities. SCSh2. Students will use standard safety practices for all classroom laboratory and field investigations. SCSh3. Students will identify and investigate problems scientifically. SCSh4. Students will use tools and instruments for observing, measuring, and manipulating SCSh5. Students will demonstrate the computation and estimation skills necessary for analyzing data and developing reasonable scientific explanations. SCSh6a. Write clear, coherent laboratory reports related to scientific investigations. SCSh6b. Write clear, coherent accounts of current scientific issues, including possible alternative interpretations of the data. SCSh8b. Scientific researchers are expected to critically assess the quality of data including possible sources of bias in their investigations hypotheses, observations, data analyses, and interpretations. SCSh8e. The ultimate goal of science is to develop an understanding of the natural universe which is free of biases. SCSh8f Science disciplines and traditions differ from one another in what is studied, techniques used, and outcomes sought. Complementary Standards SC1b. Identify substances based on chemical and physical properties SC5. Students will understand the rate at which a chemical reaction occurs can be affected by changing concentration, temperature, or pressure and the addition of a catalyst 2

3 Understanding and Goals Unit Understandings, Themes, and Concepts determines A chemical bond is a force holding atoms/ions in a combined state. The bond may be ionic or covalent, or may be categorized along a continuum between ionic and covalent. Atomic structure dictates bonding, which in turn determines the structures of compounds (and diatomic molecules of elements), and structures determine the compounds properties. In a chemical change, bonds are broken and new bonds are formed, matter is conserved, and energy is always involved. Indicators of chemical change include color change, formation of a precipitate or water, evolution of a gas, and changes in energy. (See teacher note below.)* Most reactions can be described by five basic patterns of reactions. Chemical formulas reflect the conservation of matter in bonding and can be determined experimentally. *Teacher Note: The same indicators may be observed in numerous physical changes. However, the important difference here is that the color change, the odor produced, the precipitate formed, or the gas evolved, results because a new product was formed in the reaction; whereas these indicators in a physical change result because the same substance is in a different state or condition. Point out this crucial difference throughout this unit. An example of this would be that when silver nitrate and sodium chloride react, the products are silver chloride ( a white precipitate), and sodium nitrate. The new precipitate indicates a chemical reaction. When sand and water are mixed and agitated, the sand is suspended in the water. Over time the sand settles (precipitates to the bottom) but it is still sand. This is a physical event. Students should understand that energy is involved in both physical and chemical changes. Essential Questions What determines how elements are attracted to each other in compounds? How do elements bond? (What is a chemical bond, anyway?) How are properties related to bonding? How are formulas written to reflect the composition of compounds? How are ionic and molecular compounds named? How do groups of atoms form polyatomic ions and why do they act as a single unit when bonding with other ions? How can you tell if a chemical change has taken place? What are indications that chemical reactions have taken place? How are formulas determined experimentally? What do glucose, acetic acid, and formaldehyde have in common? (How can you determine if the molecular formula is a multiple of the empirical formula?) Where do acids and bases fit into the organization of compounds? How are formulas for acids and bases written and how are they named? Balanced Assessments 3

4 Method types Informal Observations Dialogue and Discussion Selected Responses Constructed Responses Self-Assessments Monitor progress during formula writing practice Monitor practice during mole conversions Student/teacher Peer conferencing Whole group discussion Discuss bonding; monitor student understanding through questioning Discussion during acid/base lab check for understanding Teacher prepared items on quizzes and summative test to assess specific unit content Writing: How is salt different from sugar? Graphic organizer: properties of acids & bases Formula construction Ionic/covalent properties Indications of chemical reaction lab Practicing mole conversions Practicing writing formulas Practice balancing equations Discuss physical and chemical properties; monitor student understanding through questioning Formula of a hydrate lab Quizzes on formula writing /naming, empirical/ molecular formulas Formula mole conversions Empirical formula of magnesium oxide calculation Balance equations identify reactions Analysis of reactions task Unit Performance Task(s) Unit Performance Task Titles Task 1: Water You Thinking? Task 2: Reaction Types Concept Map Performance Task Task 3: Analysis of Reactions ( from bag reactions) Description/Directions: Task 1- Water You Thinking: Student writes an analytical essay to explain how atoms and ions bond. The title alludes to the uniqueness of the bonding in and between water molecules and should prompt the students to consider the range of possibilities that exist in bonding. 4

5 Task 2: Students summarize the understandings of this unit on a concept map of reaction types. Task 3: Students prepare an analysis of all the reactions that occur in the Bag Reactions task. Follow the links given above or go to the appendix of this unit for details and description. Rubric for Performance Task Reaction Types Concept Map Student Work Sample with Teacher Commentary Sequence of Instruction and Learning Teacher Activities Model how the octet rule applies to ionic and covalent bonds. Student Activities Valence graphic organizer Octet game-crazy eights Discuss bonding: have students brainstorm what they already know about bonding; use this activity to lead into discussion. Model the balance of charge with ion manipulatives and demonstrate how formulas are determined. Model and discuss polyatomic ions. Explain and model IUPAC nomenclature. Demonstration: burn magnesium to form magnesium oxide; discuss the energy involved. Provide safety instruction and enforcement. Monitor and assess group work. Orchestrate lesson on dihydrogen monoxide. Review what was learned from the properties of acids & bases lab discuss in further detail. Model the stoichiometry for determining empirical formula from experimental data. Discuss the difference in empirical and molecular formulas. Formula construction task Polyatomic Ion Bee Practice formula writing and compound naming Graphic organizer: properties of ionic and covalent compounds Ionic/covalent properties lab Calculate the ionic character of a compound Discrepant event with water Indicators of chemical change lab Properties of acids & bases lab Empirical formula lab (MgO) Calculate empirical formula from data Determine molecular formula from data 5

6 Discuss hydrate compounds. Demonstrate reactions that provide obvious examples of the evidence of chemical change. Formula of a hydrate lab Recognize reaction types, predict products and balance equations Demonstrate, discuss and model the balanced equations for examples of the five types of reactions Provide instruction and guided practice for balancing equations and working stoichiometry problems. Sequence of Activities, Tasks, and Assessments for Unit Teacher Note: Tasks in the unit are linked to their descriptions in the appendix. Throughout this unit, students will have laboratory experiences. Lab activities always require strict adherence to lab safety. Train students in safety and review before each lab experience. Safety reminders ( ) are included but do not take the place of a school s comprehensive safety plan which must be maintained and enforced in the laboratory and classroom. 1 EQ: What determines the ways that elements are attracted to each other? How do elements bond to form compounds? Understandings: A chemical bond is a force holding atoms/ions in a combined state. The bond may be ionic or covalent, or may be categorized along a continuum between ionic and covalent. Atomic structure dictates bonding, which in turn determines the structures of compounds (and diatomic elements and allotropes), and structures determine the compounds properties. In a chemical change, bonds are broken and new bonds are formed. Energy is always involved. Activate this lesson by having students review the valence electrons of the representative elements on the periodic table and complete the graphic organizer. Introduce (or review) the octet rule. Model examples of how this applies to ionic and covalent compounds. Use transparencies or a computer simulation to illustrate the difference in an atom and an ion of the same element, the transfer of electrons, and the sharing of electrons. Examples of internet resources are: Octet rule exceptions and examples and Play the Octet game to practice the concept of the octet rule. Summarize by having students total their points and clear up any questions about the correctness of their melded compounds. EQ: What determines the ways that elements are attracted to each other? 6

7 2 What is a chemical bond, anyway? How are ionic and molecular compounds named? Understandings: In a chemical change, bonds are broken and new bonds are formed, matter is conserved, and energy is always involved. Indicators of chemical change include color change, formation of a precipitate or water, evolution of a gas, and changes in energy. (See teacher note related to this element at end of the Unit themes, understandings and concepts).* Activate this lesson with a simple demonstration of a compound forming where the energy change is dramatic. Burn a strip of magnesium ribbon, making sure that the students observe the strip of magnesium before the reaction and the white powder after the reaction. Make sure students realize that oxygen from the air is the second reactant. Teacher note: Observe strict fire safety. Clean the magnesium ribbon with steel wool prior to the demonstration for best results and do not allow students to observe the white flame directly. Shield the actual flame from direct view. Elicit responses from the class about what they think is happening. Clarify as needed. Write the formula, for the product, MgO, on the board. The equation for the reaction can be given and discussed as a preview to the study of reactions. 2Mg + O MgO Discuss conceptually the net exothermic nature of the reaction. Point out that energy is required to change magnesium atoms into magnesium ions, and to change molecules of oxygen to separate atoms of oxygen. However, a greater amount of energy is released as the electrons from magnesium are gained by the oxygen atoms to form the stable compound, magnesium oxide. The ionic bonds in the compound are the force of attraction between the ions of opposite charge. Introduce the IUPAC conventions for naming binary ionic compounds and continue the lesson with the use of models. See for the formula model construction activity. Commercial versions of this activity are available or they can be made. This activity allows students to understand that when ions combine, the charges have to balance for them to form a compound. It also leads directly to formula writing. Go over the transition metals that have more than one common charge and relate this to their electron structure, and the filling inner orbitals. Have students practice writing formulas and names for compounds that contain these transition metals. Summarize lesson with a formative assessment giving students a new group of compounds for which they must write the formulas. Check these quizzes before the class meets again in order to adjust or re-teach as needed before assigning a summative assessment. Resources: Predicting formulas for ionic compounds Naming ionic compounds 3 EQ: How do groups of atoms form polyatomic ions and why do they act as a single unit when bonding with other ions? Understandings: 7

8 A chemical bond is a force holding atoms/ions in a combined state. The bond may be ionic or covalent, or may be categorized along a continuum between ionic and covalent. Atomic structure dictates bonding, which in turn determines the structure of compounds (and diatomic elements and allotropes), and structures determine the compounds properties. Introduce some familiar tertiary ionic compounds: baking soda, Epsom salt, chalk, etc. Write their formulas on the board, explaining how the polyatomic ion is bonded in the compound. Explain that the atoms within the polyatomic ion are bonded covalently to each other, but that overall they have (or lack) at least one extra electron, and act as a single unit in the role of a negative or positive ion in the compound. Instruct students in the IUPAC conventions for writing these formulas and naming these compounds. Students practice writing formulas and naming tertiary compounds. Homework (can be differentiated): Assign the making of flashcards for the polyatomic ions that students will be required to remember, or use frequently. Ticket-out-the-door: Write formulas for one binary compound, one compound containing one polyatomic ion, and one formula for a compound that contains two different polyatomic ions. Resource: Polyatomic 4 EQ: Why is salt different from sugar? (How are properties related to bonding?) Understanding: Atomic structure dictates bonding, which in turn determines the structure of compounds (and diatomic elements and allotropes) and structures determine the compounds properties. Activation activity: Polyatomic ion formula bee. Self-assessment or formative assessment on formula writing. Resource: Polyatomic ions Performance task -Properties of compounds Prelab: Preface this lab with safety instruction and a mini-lesson on any equipment, techniques, or procedures that students will need. Post lab: Students complete a lab report. Teacher note: Resource for ionic compound properties: Atoms and subatomic particles 8

9 EQ: Why is salt different from sugar? (How are properties related to bonding?) Understanding: Atomic structure dictates bonding, which in turn determines the structure of compounds (and molecules of elements), and structures determine the compounds properties. 5 Activate this lesson by having students recall the properties of ionic and covalent compounds and discuss. Then students create their own graphic organizer to summarize this information. Ask What causes the differences? Entertain any observations made by the class. Review (from day 1) the nature of the covalent bond. Compare the force of attraction found between ions in ionic compounds with the attraction for shared electrons in covalent compounds to guide the discussion about the differences in the general properties of ionic and covalent compounds. Introduce the table of electronegativities and model the use of this table to predict the character of the bonds in a compound. If not already covered in the discussion of covalent bonding, explain the bonding of the seven diatomic elements. ( hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine). Students practice using the table and predicting whether a given bond is ionic, polar covalent, or pure covalent. Summarizing task: For the compounds used in the Properties of Compounds Lab, calculate their degree of ionic character and rank them from most ionic to pure covalent. Write a summarizing paragraph relating this new information to the properties that were observed in the lab. EQ: What makes dihydrogen monoxide so unique? Understanding: Atomic structure dictates bonding, which in turn determines the structure of compounds, (and diatomic elements and allotropes), and structures determine the compounds properties. Activate this lesson by reporting to the class some astounding properties of dihydrogen monoxide (also known as hydrogen hydroxide): 6 Is present in cases of excessive sweating and vomiting A major component of acid rain Can cause severe burns in the gaseous state Accidental inhalation can kill you Primary contributor to erosion Decreases effectiveness of automobile brakes Is associated with major cyclonic events May dissolve metal ions especially in the presence of road salt Reacts violently with certain metals, such as sodium and potassium Ask students if they have ever come in contact with this compound. If the students have not already realized that the compound in question is water, ask them to write the formula for it using the rules they have learned. Once the identity of the compound is understood, ask students to list the beneficial functions of water. List these on the board. 9

10 Using this list, discuss the unique properties of water and how these properties are related to the functions of water. Discuss the polar covalent bonding and hydrogen bonding and how these relate to capillarity, temperature regulation in the body and in the environment, and water s ability as a solvent. Students carry out the discrepant event with water to reinforce and summarize the properties of water. To extend and differentiate this lesson, as time allows, or to consider for a project near the end of the year, the Dihydrogen Monoxide Environmental Issue Project can be done. Teacher Note: See for more on this project. StudentsDihydrogen Monoxide Environmental Issue Project really get into this lesson on the importance of nonbiased data! 7 EQ: How are ionic and molecular compounds named? Understanding: Science disciplines and traditions differ from one another in what is studied, techniques used, and outcomes sought. Activate this lesson by reviewing how ionic compounds are named. Review the rules for naming a compound containing a metal that can have more than one common charge. Provide more practice as needed. Introduce the IUPAC nomenclature for covalent compounds. (Remind students that water is a notable exception.) Model the naming process. Students practice. Monitor, adjust, re-teach, differentiate. Ticket-out-the-door: Give students a mix of formulas for ionic and covalent compounds for which the students will write the names. Also assign the names of some compounds for which the students will write the formulas. Teacher note: Most texts provide flowcharts that are good graphic organizers for naming and formula writing. These can also be found on the internet. EQ: Where do acids and bases fit into the organization of compounds? How are formulas for acids and bases written and how are they named? Understanding: Atomic structure dictates bonding, which in turn determines the structure of compounds (and molecules of elements), and structures determine the compounds properties. 8,9 Introduce the ionic nature of acids and bases. Ask students to refer to their data from the properties of compounds lab. Were the NaOH and the HCl solutions conductors or nonconductors? What does that indicate about the kind of compounds they are? Discuss the traditional definition of acid and base, emphasizing the role of the dissociated ions in solution. (Review the basics of solutions if needed.) Demonstrate the physical and chemical properties of acids and bases. Students record their observations on a graphic organizer or VENN diagram to summarize these properties. Students conduct an exploratory lab on properties of acids and bases. Test a series of aqueous solutions using litmus, or other indicators; check conductivity; mix equal volumes, 10 ml, of 0.l M HCl with 0.1 NaOH. Test the resulting solution with the 10

11 indicator(s). Resource: Most lab books have a version of this lab. Teacher note: Acids, bases, ph, etc. will be covered in greater depth in a subsequent unit, but are introduced here in the context of bonding, properties and formulas. Teacher note on safety: Review and require students to follow all appropriate lab safety rules, including the wearing of goggles and aprons, clothing safety and the handling of corrosive chemicals. Students must be thoroughly knowledgeable about the use of safety equipment including the shower, eyewash, sinks, and fire extinguisher. EQ: How are formulas for acids and bases written and how are they named? Understanding: Atomic structure dictates bonding, which in turn determines the structures of compounds (and diatomic elements and allotropes), and structures determine the compounds properties , 12 Time neede d to teach this lesso n will vary based on the needs of the class. Activate this lesson by having students summarize what they learned about acids and based in the lab. (Informal assessment) Clarify and re-teach as needed. Explain how acid formulas are written and how they are named. Connect the tertiary acids back to their corresponding polyatomic ions. Model the use of a flowchart for naming acids and bases. (found in most texts or online). Students practice this skill; teacher monitors, facilitates, adjusts, and re-teaches. Students summarize by writing the formulas and names for three binary acids, Two tertiary acids, and one base. EQ: How are empirical formulas determined experimentally? Understanding: Chemical formulas reflect the conservation of matter in bonding and can be determined experimentally. Activate lesson with a review of the mole concepts (see unit, Finding Order). Model the calculation of gram formula mass. Review and practice dimensional analysis. Students practice. Monitor, assist, adjust, re-teach as needed. Lab: Students will experimentally determine the empirical formula of a compound. A suggested lab that is found in many chemistry resources is the determination of the empirical formula of magnesium oxide. Students carry out the lab. Based on the mass of the original magnesium and the mass of the product, magnesium oxide, students will determine the empirical formula for this compound. Teacher note on safety: Review and require students to follow all appropriate lab safety rules, including the wearing of goggles and aprons, clothing safety, procedures for handling chemicals, fire safety, and lab burner safety. Students must be thoroughly knowledgeable about the use of safety equipment including the shower, eyewash, sinks, and fire extinguisher. Model the stoichiometry for determining the empirical formula from the mass data 11

12 obtained in the lab. The students calculate their own data. Collect data from all groups on a master data table for the class to analyze. Model stoichiometry for percent composition problems. Graphic organizers for working the problems will be useful. Students practice a variety of examples. (There may me a need for differentiating the problems as students progress in their understanding.) Students turn in their percent composition problems for formative assessment EQ: What do glucose, acetic acid, and formaldehyde have in common? (How can you determine if the molecular formula is a multiple of the empirical formula?) Understandings: Chemical formulas reflect the conservation of matter in bonding and can be determined experimentally. Atomic structure dictates bonding, which in turn determines the structures of compounds (and diatomic elements and allotropes), and structure determines a compound s properties. Activate lesson with by asking students to list what they know about these three compounds. Then inform the class that all three have the same empirical formula, CH 2 O. Build on the understandings developed thus far in this unit to discuss the importance of recognizing that properties are tied to structure, and that the true molecular formula can be a multiple of the empirical formula. Teach the stoichiometry for determining molecular formula. Students practice. Monitor, assist, adjust, re-teach as needed. Students turn in work for formative assessment. Homework Practice and study for quiz on determining formulas from empirical data. Give quiz on formula writing and naming and calculating empirical formulas and molecular formulas. Assign the performance task, Water you thinking? Introduce this task by reviewing the nature of water and the way its atoms are bonded in the molecule and how the water molecule is attracted to other molecules. Explain that the title draws on this understanding about water. See task details in appendix. Students will work on this task after the quiz. EQ: How are formulas written to reflect the composition of compounds? Understanding: Chemical formulas reflect the conservation of matter in bonding and can be determined experimentally. Activate this lesson by using copper(ii) sulfate pentahydrate to demonstrate what happens when hydrates are heated. Show what happens when water is added to the anhydrous form. Discuss how hydrate formulas are written and how they are named. Lab: Empirical formula of a hydrate (A version of this lab is found in many lab books.) 12

13 Teacher note on safety: Review and require students to follow all appropriate lab safety rules, including the wearing of goggles and aprons, clothing safety, procedures for handling chemicals, fire safety, and lab burner safety. Students must be thoroughly knowledgeable about the use of safety equipment including the shower, eyewash, sinks, and fire extinguisher Use this day for students to review, get help, or complete labs, in preparation for a summative assessment over bonding, compounds (naming and writing formulas), and acids and bases. Summative assessment on bonding and formulas; Water You Thinking Task is due. EQ: How can you tell if a chemical change has occurred? Student writes an analytical essay to explain how atoms and ions bond. The title alludes to the uniqueness of the bonding in and between water molecules and should prompt the students to consider the range of possibilities that exist in bonding. l if a chemical change has taken place? What are indications that chemical reactions have taken place? Understandings: Matter is neither gained nor lost in a chemical reaction but atoms and ions are rearranged into different patterns, bonds are broken and /or formed, and energy is stored or released. Evidence or indicators of chemical change include color change, formation of a precipitate or water, evolution of a gas, and changes in energy. * See teacher note found at end of the Unit Understandings, Themes, and Concepts. Begin this lesson with a DO NOW: (A DO NOW is a task that is assigned for students to do immediately when the bell rings. It should be self explanatory, freeing up the teacher for other routine tasks. The DO NOW is usually written on the board or projected. It is productive way to use the first moments of class in a way that will focus the lesson. In this case, the compounds that are the focus of the DO NOW will be used during this lesson.) The DO NOW: The teacher lists these compounds names on the board before class begins, with this instruction to the students: Copy this list in your notebook and write the correct formula for each compound. Also list any properties you know for each compound. The list: sodium hydrogen carbonate, calcium chloride, water. Launch this lesson by talking about the compounds that the students have experienced thus far. Students are developing understandings about the structure and formulas of compounds and it should be clear that they are formed by dynamic chemical changes. Briefly review the results of the empirical formula labs. Explain that now the focus of study will shift to understanding chemical changes both experimentally and mathematically. Activate this lesson with a series of demonstrations that illustrate the indications of chemical reaction. Include reactions that produce light and are exothermic (combustion of magnesium) 13

14 and that produce light without obvious heat (stir commercial product containing luminol, available from lab supply companies, into water or demonstrate a light stick); produce heat, but not light (CaCl 2 and H 2 O ); absorb heat (Ba(OH) 2 + NH 4 Cl); reactions that involve dramatic color change (KMnO 4 and NaHSO 3 ); produce odors (Ba(OH) 2 + NH 4 Cl); produce a gas (decompose H 2 O 2 ); and that produce a precipitate (AgNO 3 and NaCl ). Students create a data table to use during the demonstrations. The data table should include the formulas for the reactants and products and their observations for each reaction. Teacher note: write out the substances name on the board, but do not give the formulas. Students will write the formulas for practice. Omit this step for any compounds where the student would not be expected to know how to write the formula, for example the compounds in a light stick. After demonstrating a reaction write out the word equation and have students translate it into the chemical equation by writing the correct formulas and symbols. Model balancing the equation, explaining each step. Pick the reactions you want to balance on the board to illustrate the process of balancing equations. Discuss Law of Conservation of Matter and why we need to balance equations. Stress that the coefficients can be interpreted as formula units or as moles. Students summarize their observations to be turned in for assessment. Teacher note: Do not get bogged down today in balancing equations. Today s goal is to familiarize students with the process. For some it may be a review. The next lesson will focus more on mastering the balancing of equations. Teaching strategy: To reinforce the understanding of the indicators of chemical change, immediately begin the exploratory activity, Reaction in a Bag. Explain that the students will set up a reaction in a bag that they can consider to be a reaction system. Have students summarize this lesson by writing the word equation for the reaction, and the balanced chemical equation. (Give students the names of the final products for this task. Once they have the correct formulas the equation will be balanced). Teacher Note on Safety: Review and require students to follow all appropriate lab safety rules, including the wearing of goggles and aprons, clothing safety and the handling of corrosive chemicals and how to waft to detect odors. Students must be thoroughly knowledgeable about the use of safety equipment including the shower, eyewash, sinks, and fire extinguisher. EQ: How are atoms and ions rearranged in a chemical change? What are the types of chemical reactions and why is it useful to classify reactions? 14

15 Understandings: Matter is neither gained nor lost in a chemical reaction but atoms and ions are rearranged into different patterns, bonds are broken and /or formed, and energy is stored or released. Most reactions can be described by one of five basic patterns and are identified as synthesis, decomposition, single replacement, double displacement, or combustion. A system is all the components that define what is being observed or studied. s 19, 20 Teacher Note: This lesson will consist of demonstration and lecture on the types of chemical reactions. Demonstrate the reactions of each type; then model balancing the equation. Give students models for balancing the equations. The following are some possible demonstrations and discussion points. Model and exercise appropriate lab safety throughout this lesson. If you are not familiar with a demonstration seek more information and instruction before doing the demonstration in your classroom. Students should take careful notes as the demonstrations proceed. If needed provide a guided note taking sheet. Activating strategy: The first demonstration is a good hook; it is showy enough to get the class involved. For this first demonstration write the balance equation on the board. The students will not be able to write the product formula without further explanation. See the explanation below. Use the accepted terminology for reactants, products, yields, subscript, and coefficient. Demonstration 1: Synthesis Reactions: Burn steel wool in oxygen. 3Fe+ 2O Fe 3 O 4 (s) Teacher note: Carry out this reaction in a gas collecting bottle full of oxygen behind a shield. Fill bottle from an oxygen cylinder and leave inverted on a glass plate until ready to use. If an oxygen cylinder is not available in the science department, it may be possible to obtain the oxygen from a tank in the vocational department where welding or automotive courses are taught. A third option is to first generate and collect the oxygen in the lab as a demonstration of the decomposition of potassium chlorate or hydrogen peroxide. Then go back to this reaction. Hold the steel wool with tongs until it is red hot in a burner flame and then plunge it into the waiting oxygen bottle. Use extreme care. The bottle will sometimes crack. Do not substitute any other kind of container for the gas collecting bottle. After the demonstration probe for understanding. Ask students to explain what happened. (Two substances were chemically united into one substance, new bonds were formed, etc.) Probe with questions about the energy involved, and the evidences of reaction. (New product is visible, energy was released.) Ask the students about the mass of the reactants and the products. Ask the students to propose a way to determine if the mass of the reactants and product are equal. Have them discuss their ideas. Next, show students steel wool that has been allowed to set in a moist environment for several days. 4Fe + 3O Fe 2 O 3 (rust) 15

16 Explaining the results and balancing the equations: At this point the teacher can go into more detail about the Fe ++ and Fe +++ ions and the energy differences involved in the formation of the two iron oxides demonstrated in this lesson. A third iron oxide, FeO, oxidizes to Fe 2 O 3 when exposed to air. The Fe 3 O 4 produced in the first demonstration can be thought of as a combination of Fe 2 O 3 and FeO and can be called Iron (II, III) oxide. Demonstration 2: Decomposition Reactions Decompose hydrogen peroxide rapidly by using manganese dioxide as a catalyst. Pour 250 ml of H 2 O 2 into a graduated cylinder that has a thin layer of MnO 2 on the bottom. 2H 2 O 2 2H 2 O + O 2 Discuss the reaction, have students write and balance the equation. Discuss the role of the catalyst in this reaction and expand the discussion to the role of catalysts in general. Teacher note: There are several very dramatic versions of this type of reaction. 30% hydrogen peroxide can be decomposed, but handle with caution. (A local source of 30% hydrogen peroxide is a beauty supply store where it is sold as a bleaching agent.) This demonstration is called elephant toothpaste and there are numerous versions of it on the internet. This demonstration is a good place to introduce the topics of kinetics, oxidation/reduction, catalysts and gas production or limiting reagents. Details of the reaction are found at: Resources: classes.mhcc.edu/enh/ch223_mr/s3/sp02/toothpaste_jpg.html Another variation is to chop up some liver (chicken, beef, or pork) and put into a graduated cylinder. Pour hydrogen peroxide onto the liver. The Hydrogen peroxide will decompose rapidly in the presence of the catalase enzyme which is abundant in the liver. This approach is very messy but has a certain yuck appeal. It is also a great opportunity to connect this course to a vital biochemical process. For background, refer to a biology text. A Demonstration 3: Synthesis Decomposition Pop the top on a soft drink. Pour some into a beaker. Ask students where the bubbles come from. Explain that under pressure, the CO 2 that is forced into the solution tends to combine chemically (but loosely) with the H 2 O forming carbonic acid. When the pressure is reduced (you reduce the stress on the system when you pop the top, and one of the products escapes), the carbonic acid decomposes. H 2 CO 3 CO 2 + H 2 O In the unopened can, at any given instant, both reactions are occurring in a state of equilibrium, so that this is a reversible reaction. 16

17 CO 2 + H 2 O H 2 CO 3 This is an opportunity to help students build conceptual understanding of a chemical system, equilibrium, reversible reactions, Le Chatelier s Principle, and properties of gases which are covered in greater detail in later lessons. Demonstration 4: Single Replacement Mg + 2HCl ---- MgCl 2 + H 2 Have students discuss the reaction, write and balance it. Then ask students to think back to what they learned about trends on the periodic table and predict what would happen if iron were used instead of magnesium. Discuss the activity series and how to use it to predict whether a single replacement reaction will happen. If time permits, use one class period for an activity series lab. Demonstration 5: Double Replacement K 2 Cr 2 O 7(aq) + 2AgNO 3(aq) --- Ag 2 Cr 2 O 7(s) + 2KNO 3(aq) This demonstration is most effective on a light box or overhead projector. Use a dilute solution of potassium dichromate. Use just enough to get a pale orange solution. Add silver nitrate solution using a plastic pipette. This reaction produces a vivid brick red precipitate, silver dichromate. Follow up this double replacement by stirring a small amount of NaCl into the beaker that contains the silver dichromate. Ag 2 Cr 2 O 7(s) + 2NaCl( aq ) --- Na 2 Cr 2 O 7(aq) + 2AgCl (s) The sodium dichromate will be light yellow and the silver chloride will be a white precipitate. Allow the precipitate to settle to show the class. Discuss the ionic nature of this reaction and demonstrate how this type of reaction can be represented in ionic form. Introduce the idea of net ionic equations and illustrate with these reactions. Demonstration 6: Combustion Define combustion as exothermic, rapid oxidation. Burn several different hydrocarbon compounds to illustrate combustion where water and carbon dioxide are formed. Light a paraffin candle, light a lab burner, strike a match. Since paraffin is a mixture of alkanes, its formula is represented as C n H 2n+2. The generic equation for the combustion of an alkane compound is: 17

18 C n H 2n+2 + O CO 2 + H 2 O Explain that the combustion of methane, the simplest alkane, which is often added to propane, would react with oxygen in the following way. CH 4 + 2O CO H 2 O Propane which is the gas used in many labs, would react in this way: C 3 H 8 + 5O CO 2 + 4H 2 O Have students list all the similarities of these reactions. Have the students develop the definition of combustion of a hydrocarbon based on these similarities. After this definition is established, the following applications and extensions can be addressed. Explain the difference in complete combustion and incomplete combustion of a hydrocarbon. Discuss the conditions under which each occurs. (Incomplete combustion occurs at lower temperatures and when the oxygen supply is the limiting reagent. Under these conditions carbon monoxide is produced. This is a real world application of the effect of a limiting reagent and/or the effect of temperature on a reaction.) Compare cellular respiration to combustion of sugar as an extension and connection to biology. Point out that not all combustion reactions are hydrocarbon combustions. The burning of steel wool was a combustion reaction as well as a composition reaction. Another demonstration of combustion of a non-hydrocarbon is the burning of sulfur in an oxygen bottle; set this up the same way as the steel wool was set up for the first demonstration. Have students extend their definition to compounds that are not hydrocarbon compounds. Summarizing Task: List several reactions on the board. Have students write the word equation, the chemical equation and then practice balancing these. The final step is to identify what kind of reaction each is. Examples: Combustion of magnesium Addition of zinc to hydrochloric acid The reaction between lead nitrate and potassium iodide Formation of calcium oxide and carbon dioxide from calcium carbonate. Resource for many other demonstration options: Links - Demonstration Experiments - Chemistry Fak_IV/Organische _Chemie/Didaktik/ Keusch/link.htm 18

19 21,22 E.Q. How are atoms and ions rearranged in a chemical change? What is a balanced chemical equation and what does it tell us? What are the types of chemical reactions and why is it useful to classify reactions? Understandings: Matter is neither gained nor lost in a chemical reaction but atoms and ions are rearranged into different patterns, bonds are broken and /or formed, and energy is stored or released. Most reactions can be described by one of five basic patterns and are identified as synthesis, decomposition, single replacement, double displacement, or combustion. Activate this lesson with this hook: Have students go back to their notes from 18. Review the reactions and ask students to determine what kind of reactions they were. Teach the details of balancing equations. There are many useful website resources. One such source that can be used to teach and reinforce conservation of matter, the types of reactions and the skills of balancing a chemical equation is: Use distributed practice; monitor and adjust instruction so that all students develop this skill and understanding. Summarize lesson with a brief formative assessment over balancing equations. Homework: Give students sets of reactions to write the formulas, determine the kinds of reactions and balance the equations. This assignment could be differentiated in level of complexity and length. Also assign a quiz over balancing equations to be given during the next class. 23 E.Q. How are atoms and ions rearranged in a chemical change? What is a balanced chemical equation and what does it tell us? What are the types of chemical reactions and why is it useful to classify reactions? Understandings: Matter is neither gained nor lost in a chemical reaction but atoms and ions are rearranged into different patterns, bonds are broken and /or formed, and energy is stored or released. Most reactions can be described by one of five basic patterns and are identified as synthesis, decomposition, single replacement, double displacement, or combustion. Today students will carry out a laboratory exercise to gain first hand experience with the five types of reactions. There are various versions of this lab available in most lab books or on-line. Homework: Assign performance task, Analysis of Reactions to be turned in on

20 24 Teacher note on safety: Review and require students to follow all appropriate lab safety rules, including the wearing of goggles and aprons, clothing safety, procedures for handling chemicals, fire safety, and lab burner safety. Students must be thoroughly knowledgeable about the use of safety equipment including the shower, eyewash, sinks, and fire extinguisher. This day will be used for students to complete lab work and reports. Time can be used to review the understandings of this unit, and to work on the performance task, Analysis of Reactions. Teacher will conference with individuals to facilitate this task. 25 Summative Assessment: Test over compounds, reactions, and equations. Constructed response item to include is the Reaction Types Concept Map. Misconceptions Students may think that if a balanced chemical equation can be written, the reaction can occur. Students may think of these pairs of words as synonyms: atom and element molecule and compound Students may think that the elements are found in their elemental form in nature. Language Chemical bond; ionic bond; covalent bond; molecule; formula; ion; cation; anion; precipitate; empirical formula; molecular formula; subscript, hydrate, anhydrous, reactant, product, yield, coefficient Web Resources: This website has a wealth of links and resources for this unit as well as for other chemistry topics. Ionic bonding and properties: Atoms and subatomic particles United streaming has several video clips available on chemical reactions (including teacher guides and black line masters for students). systems can obtain access and passwords. This site gives a comprehensive treatment of the topics in this unit. for 2 and other helps

21 Other Resources The formula construction materials are available from various chemistry supply companies in kits, but can be homemade. Most lab books have an empirical formula lab, and a formula of a hydrate lab available. 21

22 Appendix PERFORMANCE TASKS FOR UNIT THREE Properties of Compounds Give students labeled samples of ionic and covalent compounds. Do not indicate whether they are ionic or covalent. Some examples include sugar, salt, vinegar, dilute HCl, dilute NaOH, and oil (if you don t mind getting messy!). Student pairs or teams will design procedures for testing and recording data on the properties such as conductivity, solubility, hardness, brittleness, and melting point. After teacher approval, students will carry out their procedures, and collect their data. In order to analyze their data, students should research the general properties of ionic and covalent compounds. After doing this, each sample should be identified as ionic or covalent. Students incorporate all these steps into a complete lab report. Teacher notes: a. All safety rules must be strictly enforced, including the wearing of goggles and aprons, fire, heat, and electrical safety, and safe handling of chemicals and glassware. I mini-lesson on some of the necessary techniques, equipment, and procedures should precede this lab. b. Conductivity testers can be constructed using 9-volt batteries, and LED bulbs. c. Construct rubric and discuss with students during the pre-lab. Dihydrogen Monoxide Environmental Issue Project This project can be done if time allows and could be a project done near the end of the year. It impresses on students the importance of multiple data sources and careful data analysis. Students research DHMO and write a persuasive letter with a petition to ban DHMO. They must get at least 10 adults to sign their petition. Only after obtaining signatures do they reveal the common name for DHMO. This can be done by sending an official memo from the chemistry department explaining that DHMO is really water, and that the students were conducting an exercise in the importance of basing judgments on thorough data. Students love to pull this one on teachers and administrators. As this activity gets repeated, successive groups of students will have to seek out the new teachers and other adults to find those who do not already know about DHMO. For more on DHMO go to 22