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.

An Example of Project Based Learning in Groups

Here is a lesson for use during units on classification.  Students should find it challenging, fun, and rewarding!


Classification and Cladistics - Who is Related?

Standards addressed in this lesson:

NGSS: Science and Engineering Practices (9-12):

Practice 2. Developing and using models

Modeling in 9–12 builds on K–8 experiences and progresses to using, synthesizing, and developing models to predict and show relationships among variables between systems and their components in the natural and designed worlds.

Develop, revise, and/or use a model based on evidence to illustrate and/or predict the relationships between systems or between components of a system.

NGSS: Disciplinary Core Ideas (9-12)

LS3: Heredity: Inheritance and Variation of Traits

LS3.B: Variation of Traits

Environmental factors also affect expression of traits, and hence affect the probability of occurrences of traits in a population. Thus the variation and distribution of traits observed depends on both genetic and environmental factors. (HS-LS3-2),(HS-LS3-3)

Learning Outcomes

Students will be able to:

Develop a model of evolutionary relationships of marine organisms.

Describe how groups with similar traits are related based on common ancestry

Infer how environmental factors affect traits of organisms.

Essential Question

How have the traits of marine organisms changed as life has advanced, and how do we use them to develop a model of how these animals evolved?

Lesson Description

Cladistics and Taxonomy are two sciences that are constantly evolving, and as such are always a source of debate and disagreement in the scientific community.  In the present day, the use of DNA analysis has answered many questions about relationships between animals and their lineages, however this wasn’t always the case.  While the Linnean system is still used occasionally as a kind of file cabinet for classifying species, organizing organisms into clades according to their lineages is becoming far more common as DNA gives us direct solid evidence.  It wasn’t always this way, however, and scientists often struggled to classify animals as they had little more to go on than physical features and appearances.

During this project, students in small groups will be tasked with taking a group of 30 marine organisms and organizing them into a cladogram, which shows not only relationships but shared traits possessed by different clades.  The goal is to get them as close as possible to what their DNA suggests without having any DNA data available – they can only go by physical appearance like scientists years ago.  They are given a couple starter traits to look for:  symmetry and overall body plan. 

Grouping for this project can be done with mixed, heterogeneous groups or by using homogeneous groups of students of similar level.  The general design is for heterogeneous groupings with students supporting each other, however uniform groups can be used with varying levels of difficulty added for more advanced students.

The Lesson in Action

The students are given a large piece of butcher or construction paper, and the 30 organisms on a sheet of paper.  They cut out the 30 organisms and start to organize them into groups.  During this period, students should question each other to try and figure out which animals form groups of closely related organisms.  Some of the questions they should ask:

What is the general shape of the organism?
What supporting structures does the organism possess? (shells, bones, exoskeletons)
How does the organism move?
Where does the organism likely live?
How does the organism get its energy?
Does the organism have advanced features? (warm blood, intelligence, social groups)

Other questions can be suggested as necessary. Students will struggle at first, so I suggest they break them into the two large groups of vertebrates and invertebrates, and then go through the questions from there.

Once the students are satisfied with their classification, they should arrange them on the butcher paper and insert lines in the form of a cladogram showing what they think their relationships are according to their traits.  On the lines of the cladogram, they should be noting the traits of each group, gleaned from the questions they asked.  Major traits that are conserved should go on the main line of the cladogram, while minor group traits go on the branches.

Once they get their cladogram complete, they write two paragraphs which describe their classification system and why they put each animal where they put it.  The paragraphs should explain which major traits have appeared as new animal groups evolved, as well as which specialty traits the groups of organisms possess.

Information Sharing

At the culmination of the project, students should share their findings with other groups.  Constructive discussion should take place, and as the students present their cladograms and paragraphs, the teacher should be recording which groups were popularly formed by the students and the reasons those groups chose them.  After the data are shared, the teacher should show the students a cladogram of the true evolutionary relationships.  While very few student groups will come close to the true cladogram, let them know that science is trial and error, and without DNA evidence scientists made the same classifications they did for years.  Students should then write a short reflection comparing their findings to the true cladogram, and evaluate what they learned and would do different if they were presented with this project again.

Optional, for one to one classes: After the final discussion, students should be invited to paste their paragraphs into iBooks author, along with a photograph of their cladogram.  The teacher can then assemble these into an iBook for the period, which can be published on iTunes.

Lesson Pacing

The lesson takes two to three block periods

• Project explanation by instructor: 10-15 minutes
• Prepare cutouts and classify into groups: 30-40 minutes
• Affix cutouts to butcher paper, draw in cladogram, and label traits: 20-30 minutes
• Writing of descriptive paragraphs: 20-30 minutes
• Presentation of cladograms and findings: 5-10 minutes per group
• Project wrap-up, comparison to true cladogram: 20-30 minutes
• Student reflections: 15 minutes

This project is largely student based, the instructor should support the students as needed, but let them work through things without offering too much information

Grouping and Differentiating the Project

Groups can be done many ways, but generally I let the students choose their own groups provided the makeup of the group is acceptable.  All groups must be cleared through me before they start the project.  

The project can be differentiated in several ways.  I generally ensure heterogeneous groups, where the more capable students are helping their peers who are more challenged with the project.  Alternatively, groups can also be homogeneous, with more detail being required of advanced students, while certain aspects of the project can be removed for lower grade levels or for classes with students with learning challenges.  Layers of difficulty can also be added/removed from the project, such as:

• requiring multiple traits for each group, or simply requiring students to only include major traits
• requiring advanced students to try and figure out what the animals are without research, while allowing challenged students the scaffold of iPads or other research methods
• adding or removing elements from the written paragraph according to student needs

A link to the project and the animal cutouts can be found here:

Classification of Organisms

 Animal Images