Teaching Plan: Balancing Chemical Reactions

Teaching Plan: Balancing Chemical Reactions

Standards:

NGSS: Disciplinary Core Ideas
    PS1: Matter and its Interactions
PS1.B: Chemical Reactions

Chemical processes, their rates, and whether or not energy is stored or released can be understood in terms of the collisions of molecules and the rearrangements of atoms into new molecules, with consequent changes in the sum of all bond energies in the set of molecules that are matched by changes in kinetic energy. (HSPS1-4),(HS-PS1-5)

The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions. (HS-PS1-2),(HS-PS1-7)


Pre-Assessment – short assessment where students have to identify different types of chemical reactions (replacement, synthesis, decomposition, etc.)

Section I – Balancing single-replacement, double-replacement, synthesis, and decomposition reactions

A. Presentation: Balancing chemical reactions

Presentation in Pear Deck which describes how to balance chemical reactions.  All presentations follow the gradual release model.  Included in the presentation are:
• examples of how to balance a reaction
• Short videos on YouTube visually depicting chemical reactions and what balancing them entails
• a live draw-it slide where the teacher can balance a reaction while the students watch
• Several draw-it slides where the students can either work in pairs or independently to balance reactions, which are then reviewed by the class
B. Independent practice time on blackboard worksheet, which releases an answer key to the students that they can view once they have submitted their assignment.  Students who are struggling can be grouped together for small group instruction while students are working independently.

Section II – Balancing combustion reactions, and reactions with the same element on both sides

A. Presentation: Balancing complex chemical reactions

Presentation in Pear Deck which describes how to balance chemical reactions when the same atom is present multiple times on the product or reactant side.  Included are:
• Visual animations of the reaction types that are more difficult to balance
• a live draw-it slide where the teacher can balance combustion while the students watch
• Several draw-it slides where the students can either work in pairs or independently to balance complex reactions, which are then reviewed by the class

B. Group Project (formative assessment)  – Demonstrating complex reactions
• In groups, students take atomic cutouts and arrange them on a sheet of paper showing what is happening during a complex chemical reaction.  Arrows are drawn showing how atoms are being rearranged during the reaction.  The students must perform this for 5 reactions, ranging from simpler ones to one that is very complex and will require a lot of thinking.  Once all groups have completed the project, correct diagrams will be projected for all to check their answers.

Section III – Writing and balancing net ionic equations

A. Short refresher on solubility rules for compounds

B. Presentation: What are net ionic equations, and how to balance them

Presentation in Pear Deck which describes the writing of net ionic equations by writing soluble compounds as ions, then identifying and removing spectator ions in the equation.  Presentation includes:
• A graphical depiction of separation of soluble compounds within a reaction using periodic table magnets on the whiteboard.
• Identification and removal of spectator ion magnets, which are on both sides of the reaction
• What magnets are left after removal of spectators is the net ionic equation.

C. Independent practice time on writing net ionic equations using chosen reactions from section I and II.  Students can work individually or in groups on this assignment, and can utilize their chemistry model kits to help them visualize what is going on.

Section IV – Writing and balancing oxidation/reduction reactions

A. Presentation: What are redox reactions and how are they balanced?

Presentation in Pear Deck which introduces and describes how to balance redox reactions.  .  Included in the presentation are:

• A description of redox, and the movement of electrons in a reaction
• A visual list of oxidation states and rules for the elements
• A description of half-reactions
• A stepwise example on how to balance redox reactions, including:
   o Balancing everything except O and H
   o Adding H2O to balance oxygen
   o Adding protons to balance hydrogen
   o Balancing charges with electrons
• a live draw-it slide where the teacher can balance a redox reaction while the students watch
• Several draw-it slides where the students can either work in pairs or independently to balance reactions, which are then reviewed by the class

B. Redox Practice -  a worksheet on blackboard where students use a stepwise approach to balance redox reactions.  A sample, along with a visual depiction of the reactions, is at the top of the worksheet.  Each problem has a place to write each of the 5 steps to balancing a redox reaction, and the students must complete each step to move onto the next.  The teacher does the first problem with the students to model how to do the assignment, then performs small group instruction as needed.

Assessment – Students are given an assessment with 20 reactions, 10 simple reactions in part A, and 10 complex reactions in part B.

Part A – Students must choose any 5 of the 10 reactions, and balance them correctly (4 points each).  20 points total.

Part B – Students must choose any 5 of the 10 reactions and balance them in as many ways as they can.  Points that can be earned:
Balancing performed correctly – 3 points
Net ionic equation written correctly – 2 points
Redox equation balanced correctly – 1 points
30 points total.

Students can balance all the equations and earn 35 of 50 points for a C, if everything is done correctly.
Students can earn extra points for writing and balancing net ionic equations, increasing points earned up to 45 of 50 for correctly balanced equations.
Students can earn the last 5 points by writing half reactions and balancing redox reactions, bringing them up to 100%
Students, at their option, can choose any one reaction in Part A or Part B and balance it to potentially replace any errors they may have made.