Evidence-Based Methods for teaching Balancing Equations
In this post, I have used the literature in educational research to outline the best methods for teaching balancing chemical equations to high school chemistry students in order to achieve conceptual understanding and mastery.
The Traditional Approach is not the best approach
To understand chemistry students must be comfortable representing chemical changes with chemical equations. However, the balanced equation which forms the basis of reaction stoichiometry has been identified as an area of difficulty for many chemistry students.
Many of the issues with balancing chemical equations stem from incomplete or inappropriate foundational knowledge (Read 4 Common Mistakes Students Make when Learning to Balance Chemical Equations).
Traditionally, teachers have focused on the symbolic level of representing chemical reactions and rely heavily on the use of formulaic steps in order to solve problems on reaction stoichiometry.
According to Laugier and Dumon (2004), novices tend to view balancing simple equations as the application of a set of rules, and do not make the necessary connections between the symbolic representation (the chemical formulae and reactions) and the observable chemical transformations that are occurring at the macroscopic level.
Recommendations from the Research
Research into student difficulties with these concepts recommends that educators place an emphasis on the visual aspect of chemistry by using diagrams to represent the submicroscopic level (i.e. molecular, atomic, and sub-atomic particles) (Ben-Zvi et al. 1987; Sanger, 2005).
This coincides with the research of Mayer (2002) who contends that students learn by the active selection, organization, and integration of information from auditory and/or visual inputs.
When teachers employ the use of descriptive tools such as diagrams or images learners are able to develop mental models for the concept.
Johnstone (1993) and Devetak et al. (2004) assert that by allowing students to engage with the material using multiple representations (symbolic, macroscopic, and submicroscopic) increased conceptual understanding and student performances are seen.
The Best Approach for teaching Balancing Chemical Equations
1. Start with the law of conservation of Matter by Performing an Experiment (the macroscopic level of representation).
Why do we balance Equations?
This is a great lesson introduction. Students need to understand why they are balancing equations.
Instead of explaining that "the number of atoms of each element must be equal on both sides of the equation" you need to explain why they must be equal.
Piaget and Inhelder (1974) stressed that students' reasoning is governed by their perceptual experience (macroscopic).
In the realm of balancing chemical equations, you MUST begin with a thorough explanation and demonstration of the law of conservation of mass.
I have seen many teachers gloss over the law of conservation of mass or skip it all together. This isn't beneficial as it leads to student difficulty in topics such as the mole concept and mole calculations later on.
Have students observe and verify the law of conservation of mass by doing a simple laboratory practical.
Some experiments to try out:
An acid carbonate reaction (closed and open systems)
A combustion reaction
A precipitation reaction
This specific selection is based on the discovery of the existence of student misconceptions in the research of Yarroch (1985); Piaget and Inhelder (1974); Anderson (1986); Hesse & Anderson (1992).
You can try the combustion experiment with accompanying results discussion and analysis sheet here.
Probe student's understanding of the practical
For the lab activity ask students to:
predict whether the mass of the system would change, and ask them to provide a reason for their response.
2. ask students to determine whether the law of concertation of mass has been obeyed and to account for any expected or unexpected readings seen at the end of the practical.
In the example below students were asked to assess the law of conservation of mass for the precipitation reaction which occurs between sodium sulfate solution and barium sulfate solution.
Piaget and Inhelder (1974) explain that students oftentimes harbor the misconception that when a precipitate is formed the system becomes heavier (i.e. mass increases) because "solids are heavier than liquids" .
This indicates a naïve model of matter which is dependent on student sensory perception.
By providing students with observable examples of the law of conservation of matter, and accounting for any discrepancies seen in the experimental results, you can provide students with an answer to the why do we balance equations question.
2. Show why equations need to be balanced using the symbolic level of representation
Depending on the topics you have covered or whether or not your students know how to define (and calculate) relative atomic mass and relative formula mass, the previous activity can be extended to demonstrate how a balanced equation obeys the law of conservation of mass.
To do this use simple examples where students will be required to calculate the Relative Molecular Mass for the products and reactants of an unbalanced, then balanced chemical equation as seen in the example below:
Two or three of these examples will suffice in getting your point across. This is also a good introduction to a lesson and begins to link the macroscopic with the symbolic level of representation.
3. Have students balance equations using visual representations in three phases (Submicroscopic level of representation)
Phase 1 Use Concrete Examples
This phase is optional and is usually used when introducing the topic to younger students or for students in need of remediation.
This phase involves the use of physical manipulatives such as MolyMods™ or other items ( such as candy) or digital manipulatives.
During distance learning I used this digital Google slides activity where colored shapes were used.
This is demonstrated in the video below:
With this activity each group of shapes represents the "chemical formula" and the proportion of different shapes cannot be changed.
Students begin to see the significance of coefficients/ multipliers when balancing equations.
Phase 2: Use diagrams of sub-microscopic particles.
This activity is similar to the first, but instead of using shapes, students begin to deal with actual formulae, represented pictorially in order to stimulate the visual processing channel (Mayer, 2009).
Here, students begin to make the necessary connections between the symbolic and submicroscopic levels of representation.
As seen in the video chemical formulae are represented using the pictorial representation of particles.
Students will now be able to count the atoms of each element and use multipliers (coefficients) in order to balance the equation.
Phase 3: Move on to the abstract
Once students have a good handling of using coefficients to balance these equations visually then they can move on to balancing symbol equations.
Because they were able to activate their visual learning channels during the first two phases, they will now be capable of connecting the symbolic representation with the sub-microscopic representation.
The following video demonstrates this.
You can download these Google Slides™ digital resources here.
4. Balancing Equations by Inspection (the "Ping Pong" Method)
Students should only be encouraged to balance equations by inspection when you are confident that they understand the reason behind what they are doing and have a grasp of writing chemical formulae, and the difference between coefficients and subscripts.
If your students need practice writing and understanding chemical formulae, you can check out this resource.
Balancing by inspection involves counting the number of atoms of each element in the reactants and counting the number of atoms of each element in the products then adding coefficients in order to get the number of atoms of each element equal on both sides of the chemical equation.
As with every group of students, some will have a full understanding of chemical formulae and the use of coefficients while others will simply attempt to balance the equation by trial and error.
Niaz and Robinson (1992) warn that the trial and error method (or inspection without conceptual understanding) can pose difficulties for students as it places a high demand on their reasoning ability as well as their ability to handle ratios and proportions.
If your students are experiencing difficulty balancing chemical equations or having issues solving stoichiometric problems you may need to teach this topic using multiple levels of representation in order to develop student conceptual understanding as recommended by Johnstone (1999).
All these resources can be purchased form my TPT store
Investigating the Law of Conservation of Mass Practical Activity
Introduction activity to the law of conservation of mass
Balancing Chemical Equations
Students Practice Phase 1 and 2.
Balancing Chemical Equations Add-On
Students practice Phase 3: Balancing Symbolic equations
Writing and Understanding Chemical Formulae
Address students misconceptions and difficulties when learning to balance chemical equations