OOOOH. Chemistry Math. Why does this word – stoichiometry – conjure up so many feelings of unease in our students? They come to chemistry class with each of the necessary skills; they don’t trust them.
What are these skills, you ask?
- Calculating a percent? They do this with their grades all the time
- Converting units? They just did this with moles in the previous unit. They do it all the time in math.
- Determining how much of something they can make? They do this anytime they craft something. They need to know how much product their current resources can make.
But throw in some molar masses and mole ratios, and their confidence can tank. It’s our job to keep their confidence high because they CAN complete these calculations.
And they absolutely CAN understand the meaning of the math without following a “mole map.” No shade at teachers who use them, but I hate them. I used one during my first year teaching, and so many students couldn’t answer this question: “and what does that answer tell us about XYZ?”. They would shrug their shoulders and point at the mole map.
Reference tools like mole maps or mole bridges, to me, seem to remove logical reasoning from the problem-solving process. Yes, some students need that visual aid. I get that it’s a great way of reinforcing this simple process. But y’all, some of the mole maps or mole bridges out there look so intimidating. If you want to use one, go for it. I don’t, and my students are fully capable of completing stoichiometric calculations without it.
Stoichiometry Lesson Plans
Total Duration: 8-11 days
Note: a day refers to 45-50 minute periods.
| Topic & Timeline | Tasks | Description |
| Molar Relationships 1 day | Recipe Discussion Introduction to Mole Ratios Notes + Practice | I like to start our discussion of stoichiometric relationships by displaying a recipe. It doesn’t matter what the recipe is, but I often pick something simple. As a class, we talk about how we can double or even triple the recipe. What about half? What if we only have a fraction of what the recipe calls for? How much can we make? We then move on to my Mole Ratio Notes. They look at balanced chemical reactions (the recipe) and figure out how many moles of product or reactant we need. |
| Stoichiometry and theoretical yield 1 day | Stoichiometry Notes + Practice | In a perfect world, how much product can we make? Now that my students feel comfortable with stoichiometry coefficients and ratios, we move on converting from grams of one chemical to grams of another. Or liters. Or atoms. Referring to the recipe example from yesterday, sometimes the chef/baker doesn’t use the unit provided. So they must convert it to a unit they do use. I like to teach my students stoichiometry using BCA tables or mole tables. They reinforce the idea that in order to convert from one compound to another, they must convert to moles first. I also use traditional dimensional analysis, but I find that BCA tables help my students understand stoichiometric calculations way better for the majority of my gen chem students. |
| Stoichiometry Lab 2-3 days at the start of class 1 day for calculations | Nail Lab | I love this particular lab. I don’t use a lab paper for this one- I have my students create a data table and complete indicated calculations. At the start, I tell them to record the mass of EVERYTHING. For clarification, I’ve linked a complete lab procedure for you in the task column. The gist of this lab: Students make a copper (II) chloride solution, taking care to record the mass of CuCl2 used. They then place 1-3 nails (depending on the size) in this solution. The reaction can sit until the end of class or overnight. When they are ready, students remove and clean the nails. Then they clean and dry the remaining solid. While they wait for their solids to dry, students should calculate the theoretical yield of FeCl2 from the mass of iron used. Once they have a mass of FeCl2, they determine the limiting reactant and percent yield. |
| Limiting Reactant Intro 1-2 days | Limiting Reactant Simulation (pHet) S’more Activity (paper) | After the first part of the nail lab, it’s time to adjust to reality and introduce limiting reactants to the mix. I like to use the pHet simulation because it’s more visual. Students build sandwiches and determine the limiting reactant based on what runs out. We move on to a s’mores activity. Students use a given recipe for a s’more, written as a balanced chemical reaction. They then determine the limiting reactant (graham, chocolate, or marshmallow) based on different scenarios. If you can give your students food, I HIGHLY recommend making s’mores in the classroom when you’ve finished this activity. |
| Limiting Reactants 1 day | Limiting Reactants Notes + Practice | Now let’s calculate how many grams of a product can be made based on the limiting reactant! BCA tables make this process a dream, but they are not required. Either way, students compare the theoretical yields of both reactants and select the smaller yield to determine their limiting reactant. |
| Percent Yield 1 day | Percent Yield Notes + Practice | Now we know it all—mole conversions, gram-to-gram, and even determining the limiting reactant. Finding the percent yield is the final step. Just how efficient was our reaction? Relating this to our recipe example- how much stuff did we waste? |
| Review 1-2 days | Vocabulary Practice Study Guide | I like to use the Sample of Every Type of Problem from the chemistry modeling curriculum for stoichiometry review. You have to be a member to access it. Just so you know, it that is has EVERY type of stoichiometry problem: molar mass review, mole conversions (mole, L, atoms), mole-to-mole, gram-to-mole, gram-to-gram, gram-to-liter, theoretical yield, limiting reactant, percent yield). |
| Assessment1 day |
Further Reading
The Chemistry Particle’s Guide to Teaching High School Chemistry, The Chemistry Particle
How to Increase Student Confidence In Stoichiometry with Mole Tables, The Chemistry Particle
How to Increase Student Confidence In Stoichiometry with Mole Tables, The Chemistry Particle
Using Visual BCA Tables to Teach Limiting Reactants, ChemEdExchange
5 Ways to Get Students Energized About Stoichiometry, LabsterStoichiometry Notes Bundle, TeachersPayTeachers
