Balancing Equations, Candy and an Evolving Activity

“What are we doing to help kids achieve?”

I feel like every year I face the same old dilemma. It starts with an idea in mind of what and how something should be taught. This idea is fine until it is discovered that students this year are different than students last year. The idea is changed or “tweaked”. The process is feels similar to having to “reinvent” the wheel each year. This gets exhausting.

The present group of students were struggling with balancing equations. The students could balance them on paper. They also could explain the conservation of mass with experiments. Students really struggled with showing, developing and explaining models. They were not able to clearly show or explain how the reactants are used up and the products are formed. Students did well on the Atomsmith balancing activity. It became clear through this activity that they still needed a more hands on approach.

In the past, students had completed an activity from Grand Valley State University Target Inquiry Program. The activity called “How many reactants does it take to make a product” by Sarah Toman had students physically construct and deconstruct reactants and products with models of interlocking blocks. This was met with some success in the past but it was felt that this group of students would require adaptations to the activity.

Students were given a small cup of different colored candies. They were instructed to separate out the green “G”, blue “B” and red “R” candies and the rest went in a second cup that they would get to eat later after successful completion of the activity.

The “reactor” was the only person allowed to “build” as many compounds with the green, blue and red candies. He or she had to construct as many units of the compound “R2B” and the separate element “G” as possible. Students had to record the number of compound and elements. Any extra candies could be eaten.

The “producer” had to examine the products. The formed products were the compounds “GBR” and “R2”. The ONLY person allowed to pass reactants to products was the “Gatekeeper”. The “Gatekeeper” could not tear apart any compounds from the reactants. The “Producer” was instructed to arrange the compounds and elements from the “reactors” to match the products “GBR” and “R2”. There could be no stray elements. They had to match “GBR” and “R2” or they had to stay as the reactants. Students were told to record ALL reactants and products both before and after the process.

It should be noted that we stopped as a class at three key stages. First, there was the "reactant" stage. The next stage was explaining the "gatekeeper". The last stage demonstrated how the "producer" should make the products. This was modeled at each stage by the instructor, me. Students were required to keep track of the reactants and products and record data.

At the end of these three stages, we looked at the data as a class. Students were asked to place the data in a table that had the headings: "Before", "Change", and "After" (BCA tables). This idea is used widely by people that use Modeling Instruction strategies.

So, what was the end result? One result is that over the three class periods, the activity evolved. Students from some periods had a wide range of academic and language abilities. In some cases, a bit more modeling and/or direct instruction was required on my part. I also discovered that it was really helpful for the students and myself to break the activity down into the stages of "Before", "Change" and "After". It was advantageous to have groups of four people. One person was the "Reactor", one the "Producer", one the "Gatekeeper" and one person who recorded data for the group. Each person had a specific role. Data from every group was slightly different but the data fit extremely well into "BCA" tables. Teacher notes can be found below this post as Supporting Information. The ratio of reactants to products in the "Change" row always provided the balanced equation. Students quickly picked up on the idea of "limiting reagents", "excess reagents" and fundamental stoichiometry which is our next topic. It is true that we never react "candies". Students saw a demonstration of sodium in water forming sodium hydroxide and hydrogen gas. They compared the symbols in that reaction to the one with the candies and found them to be practically identical. Finally, the candy provided a great motivator for tired students at the end of the semester.

Have you "morphed" or "evolved" an activity due to student abilities? Did you find that it worked better than expected? I would love to hear from you.

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BCA table

Megan Burns | Mon, 03/09/2020 - 14:15

Hi!

I like this idea, but I'm having a hard time conceptualizing how the students draw the BCA table at the end. How did you get 6, 24, 0, 0 then -6/3=2, -6/3=2, +6/3=2, +3/3=1, and finally: 0, 18, 6, 3?

Thanks for the comment.

Chad Husting | Tue, 03/10/2020 - 18:42

Megan - Thanks for the comment.  I totally get how this might be a bit confusing.  Sometimes it is hard to convey in writing what takes place in the classroom.  Let me try again.

Here is the balanced reaction for the "candy" reaction.

2 R2B  + 2 G    yields   2 GBR   +   1 R2

Students start with 6 R2B  and 24 G.  Before anything reacts they have 0 GBR and 0 R2

Next they start making the products and record the change.  This is the second line.

For every 6 R2B used, they also have to use 6 G and then they gain 6 GBR and 3 R2.

At the end the show what is left in the After row.  This is 0 R2B, 18 G, 6 GBR and 3 R2.

When we were finished I went back and showed the kids that if they reduce the ratio in the "Change" column to the lowest ratio (by dividing by 3) then they would get the same ratio as the balanced reaction.

I hope this helps.  Sorry for the confusion.