I decided to take a different approach to the stoichiometry unit for my chemistry sections this year. Instead of jumping right into the algorithmic approach of "3-step" problem solving, I decided to have the students complete an Excel Spreadsheet activity. It was my hope that students would see that you could actually obtain the coefficients for a balanced equation through experimental data...and if they saw this, I hoped they would see that you could then use the coefficients to solve experimental problems (the reverse process). In essence, they would see that solving a stoichiometry problem is no more difficult than setting up the correct mass relationship. Then, I could go on to show them the 3-step approach and show them how it accomplishes the same goal.
For the Excel activity, I had the students collect "experimental" data using the following simulation:
http://www.chemfiles.com/flash/mass_relationship1.swf
Students were asked to run at least five different trials and record the data in an Excel spreadsheet. Then, I had the students manipulate the data to arrive at the mass relationship for the amounts of reactants used and amounts of products produced. After determining the simplest mass ratio for the substances, I had the students calculate the simplest mole ratio. The students were then asked to balance the chemical equation in order to see the coefficients and mole ratio numbers match up. From the coefficients, I took them through calculating the simplest mass relationship to show that it was the same as all the other trials. Using the mass relationship, I asked them to answer a stoichiometry question I had asked earlier in the unit...most were able to quickly see the answer.
It seemed rather redundant to take them through so many steps that yielded the same results, but I felt is was important in reinforcing the concepts. I explained that while we wouldn't always have experimental data to help us find the simplest mass ratio...we could get the same information just as easily from the balanced chemical equation. Thereby, setting up the importance of a "balanced" chemical equation to solving stoichiometry problems.
The results so far have been very promising.
Here's a link to the movie tutorials I created for the activity:
- Setting up the Spreadsheet
- Calculating Amount of Reactants Used
- Determining the Simplest Mass Ratio
- Determining the Simplest Mole Ratio
- Wrapping it Up!
Here's an example of a completed Excel file:
- Mass Relationship Spreadsheet
Sidenote: If students don't have access to Microsoft Excel, they might find Google Spreadsheets extremely useful.
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