Lesson Plan

Predicting Products

Objectives

In this lesson, students will be able to look at chemical reactions, both on paper and in a lab setting and predict the products of the reaction. This is the last step in the process of writing a chemical equation. Students will:

  • predict the products of the five basic reaction types.

  • write correct formulas for the reactants and products.

  • balance chemical equations.

  • recognize when to incorporate diatomic molecules into a chemical equation.

Essential Questions

Vocabulary

  • Diatomic Elements: Chemical elements whose stable form at STP consists of diatomic molecules. The diatomic elements are H2, N2, O2, F2, Cl2, Br2, and I2.

  • Cations: Positive ion.

  • Anions: Negative ion.

  • Ionic Compound: A compound formed from a metal and a nonmetal.

  • Synthesis Reaction: Two or more elements/compounds combine to form a more complex product.

  • Decomposition Reaction: One chemical species breaks down to simpler elements/compounds.

  • Single Replacement Reaction: An uncombined element replaces a less reactive element in a compound, creating a new compound and a single element.

  • Double Replacement Reaction: Involves two ionic compounds (in solution) that trade cations, creating two new compounds.

  • Combustion Reaction: A hydrocarbon (or other organic molecule) burning in oxygen, producing carbon dioxide and water.

Duration

90 minutes/2 class periods

Prerequisite Skills

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Materials

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Formative Assessment

  • View
    • The formative assessment for this lesson occurs when students are answering review questions regarding ionic bonding and nomenclature, as this is an important skill for predicting products.

    • Assess student interaction and responses during the guided instruction.

    • Have students practice the material in a lab setting, as they address the chemical reactions they experienced during the previous lesson.

Suggested Instructional Supports

  • View
    Scaffolding, Active Engagement, Explicit Instruction
    W:

    Students will use their knowledge of reaction types to predict the products for synthesis, decomposition, single-replacement, double-replacement, and combustion reactions.

    H:

    The beginning of this lesson involves students reviewing nomenclature and ionic formulas. They will use this skill as they predict the products of chemical reactions. There is a guided review as well as an in-class review worksheet.

    E:

    Upon completion of the guided instruction portion of the lesson, students will work with their lab groups to complete the lab from Lesson 2. In this portion of the lab, students will complete the chemical equations from the reactions they produced in the lab demonstration in Lesson 2.

    R:

    This lesson incorporates content from Lessons 1 and 2. Students will spend the initial portion of the lesson reviewing ionic compound nomenclature and will complete the lab from Lesson 2.

    E:

    The teacher will guide each lab group as students write balanced chemical equations from the lab. Additionally, students will be assessed as they review ionic nomenclature. During the guided instruction portion of the lesson, the teacher will give feedback and answer questions regarding the practice problems.

    T:

    The lesson is tailored so that students are provided time for nomenclature review before being asked to predict products. The lesson also provides students an opportunity to look back at a lab that will ultimately synthesize the unit’s material. Additionally, there are extensions provided in the lesson that will provide students with enrichment opportunities.

    O:

    The lesson serves as a summative piece, bringing in review material from a possible previous unit, and building upon material taught in Lesson 1 and Lesson 2 of this unit. Students will review ionic nomenclature, learn new material, and then apply that material to the lab conducted in Lesson 2.

Instructional Procedures

  • View

    Much of this lesson requires students to use previous knowledge involving writing ionic formulas. They may need to start with some review, which is shown below.

    Ionic Compounds Nomenclature

    • Metals (cations) are listed first, followed by nonmetals (anions).

    • When writing ionic formulas, the final compound needs to be neutral.

    • Reference the Periodic Table to determine the ion that each atom forms.

    • The name of the metal stays the same, but the ending on the anion changes to
    “ide.”
    • For transition metals that can have more than one charge, the charge on the metal is indicated with Roman numerals.

    • For compounds with polyatomic ions, the polyatomic ion names stay the same. The endings are not changed to “ide.”

    Writing Formulas

    Show students how compounds are formed, using the crisscross method with the ions.

    A) Li and S               Li+1 and S-2               Li2S

    There must be two lithium ions for every one sulfur ion to make a neutral compound.

    B) Zn and N                Zn+2 and N-3           Zn3N2

    There must be three zinc ions for every two nitrogen ions to make a neutral compound.

    C) Al and OH           Al+3 and OH-1           Al(OH)3

    There must be three hydroxide ions for every one aluminum ion to make a neutral compound.

    Naming Examples

    A) NaCl           sodium chloride

    B) Mg3N2          magnesium nitride

    C) CaI2          calcium iodide

    D) KCl               potassium chloride

    E) NH4OH          ammonium hydroxide

    F) Na2SO4          sodium sulfate

    G) LiOH           lithium hydroxide

    If you feel that some students need reinforcement, have them complete the Ionic Compounds Practice worksheet (S-C-3-3_ Ionic Compounds Practice Worksheet and KEY.doc).

    Once you have reviewed writing and naming ionic compounds, you are ready to begin the lesson on predicting products. This lesson works through each type of reaction as a means to understanding the products.

    Say, “During this unit, you have learned to balance chemical equations and classify chemical reactions. Now, your task is to predict what the products of those chemical reactions will be and write balanced equations. We will work through all five reaction types and predict what the products will be. When we are done, your lab group from yesterday will meet to analyze the products from the lab’s reactions. Let’s start by looking at a decomposition reaction first.” Write on the board:

    CO2

    Ask students why this reaction would be classified as a decomposition reaction. They should recognize that it only has one reactant. Ask, “What are the elements from which CO2 is composed? Once you determine the atoms that make up CO2, you will write them separately as products, like this” (write on the board):

    CO2 C + O

    Continue with, “Some of you may notice that the reaction does not satisfy the law of conservation of matter. It is not balanced. Before you put a coefficient of 2 in front of the oxygen on the product side, you must know whether carbon or oxygen is a diatomic element. Please record the definition of this in your notes.” Provide students with the following definition:

      Diatomic elements: Chemical elements whose stable form at STP consists of diatomic molecules. The diatomic elements are H2, N2, O2, F2, Cl2, Br2, and I2.

    Notice that oxygen is alone on the product side but is a diatomic element. This means that oxygen is unstable alone and will be found in nature as a pair. Therefore, you will need to add a subscript of 2, not a coefficient of 2 to oxygen. The only time that you can add a subscript in an equation is when there is a diatomic element. The equation is now balanced without adding any coefficients.” Write on the board:

    CO2 C + O2

    Try these decomposition examples with the class:

    A) H2O2

    H2O2 H2 + O2

    B) Cu2O

    2Cu2O 4Cu + O2

    Tell the class, “Now that you can predict the products of a decomposition reaction, you will be able to predict the products of a synthesis reaction. Keep in mind that decomposition reactions are essentially the opposite of synthesis reactions. Decomposition reactions will have one reactant, whereas synthesis reactions will have one product. Let’s look at a few examples.” Write on the board:

    A) O2 + H2 H2O2

    B) 2Na + Cl2 2NaCl

    C) 8Fe + S8 8FeS

    Guide students to the next reaction by saying, “The next two types of reactions are single replacement and double replacement. They are closely related in terms of how you will predict the products of the reaction. Let’s try a single replacement reaction first.” Write on the board:

    NaCl + K

    Distribute copies of the metal reactivity series shown below (S-C-3-3_Metal Reactivity Series.doc).They will use it to determine how the reaction will progress.


    l3-01reactives.PNG

    Say, “In the example shown above, potassium is more reactive than sodium so it will replace sodium and the reaction will proceed. Potassium forms a +1 cation and chlorine forms a -1 anion. When they form an ionic compound, it will be written as KCl. There is a redistribution of charge when metals and nonmetals are charged (e-). “When you are predicting the products of a displacement reaction it is helpful to write out each ion and the charge that it forms. Knowing that every ionic compound is made from a cation and an anion (metal and nonmetal), you will form new products with the ions you have.” Sodium is the element that was replaced and will be written by itself as one of the products. It is not a diatomic element. The balanced reaction looks like this. The charges are shown so that you can see how they are redistributed.” Write on the board:

    Na+1Cl-1 + K0 K+1Cl-1 + Na0

    Ask students to try these practice problems. Remind them to look for diatomic elements.

    A) BaCl2 + 2K 2KCl + Ba

    B) 2AlN + 3Cl2 2AlCl3 + N2

    Students will now try predicting the products of a double displacement reaction. Write the following example on the board:

    l3-02Ageq.PNG

    It is helpful to draw arrows to show how the compounds 'switch partners.' Break both ionic compounds apart into ions.” Begin writing the following equations on the board, while continuing to instruct students. “Make a list like the one I’m writing. When you write the new products, write the cation first and the anion second and then neutralize the compound if needed.”

    l3-03AgCl.PNG

    Try a double-replacement reaction using an ionic compound containing a transition metal like copper. Students will have to look at the formula given to determine which copper ion to use.

    Cu+2O-2 + Mg+2Cl2-1

    Notice that copper in CuO is the Cu+2 ion. Therefore the balanced reaction will be:

    CuO + MgCl2 CuCl2 + MgO

    Practice reactions:

    A) Li3N + NaCl

    Li+1

    N-3

    Na+1

    Cl-1

    Li3N + 3NaCl 3LiCl + Na3N

    Introduce the last reaction by saying, “The last reaction type to predict is a combustion reaction. These are the most straightforward, because the products will be the same each time: CO2 and H2O. You will not incorporate ions because combustion reactions deal with hydrocarbons, which form covalent bonds. Here is an example.” Write the following on the board:

    CH4 + 2O2 CO2 + 2H2O

    Note: For the purpose this lesson, the products of combustion reactions will ALWAYS be carbon dioxide and water.

    At this time, direct students to form the lab groups they were in on the previous day. They should work together to complete the balanced reactions for each of the six reactions from the lab. Walk around and guide students and answer questions. Remind them to watch for diatomic elements and to use their valence sheets (S-C-3-3_Valence Sheet.doc), and also the periodic table to look up the correct charges for each ion.

    Extension:

    • All of the practice reactions require students to predict products of a chemical reaction using formulas. You may choose to incorporate the same reactions, including chemical names as well as formulas. This will allow students to practice naming formulas.

    • This lesson refers to the metal reactivity series. You may wish to incorporate a nonmetal reactivity series with some of the halogens. Information is available at

    http://www.nelsonthornes.com/secondary/science/scinet/scinet/reaction/react/halogs.htm

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DRAFT 11/19/2010
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