A discussion of how students solve stoichiometry problems.
In my class, I use the illustration of a mountain to help students push through the challenges of chemistry. Stoichiometry is the top of chemistry mountain. As we progress through the year, I say things like “the mountain is getting steep here!” or “there is not a lot of oxygen up here!” or “I will carry you up chemistry mountain if I have to!” to keep students motivated. When students finally get to the top of chemistry mountain (mid quarter 3), the air is thin, they are tired and they are ready to base jump off the mountain (see illustration from a former student below).
Inspired by Ben Meacham's post on stoichiometry, I looked to modify the lab sequence for my IB Chemistry class for our unit on stoichiometry. I will describe my experience modifying a typical empirical formula lab, along with using a modified version of the lab Ben shared.
Teaching students the proportional reasoning skills needed for stoich doesn’t have to be that daunting. By adjusting how your students talk about stoich, you will adjust how they think about it; eventually, they’ll proportionally reason in a more effective manner.
This post was submitted for the 2017 ChemEd X Call for Contributions: Creating a Classroom Culture.
In a recent post, I shared sample quiz questions as to how I have differentiated assessment within the mole unit. Here, I share a specific multi-day sequence within the stoichiometry unit. I have written extensively about the project that drives this unit (within the following blog posts: Why consider trying project based learning?, Backwards planning your PBL unit - An Overview of an Entire Unit and What ARE my students actually learning during this long term project (PBL)?), but very little about specific learning tasks. Below is a two day sequence of stoichiometry practice that I set up in my classroom. Stations are set up around the room and students rotate as necessary.
A few months ago I was searching the internet, looking for a better way to teach stoichiometry to my pre-AP chemistry students. While my methods of dimensional analysis “got the job done” for most students, I would still always lose students and many lacked true understanding of what was happening in the reaction. I wanted to try something new that would promote a better chemical understanding. In my search for this elusive stoichiometry method, I came across Dena Leggett’s ChemEd X blog post entitled “Doc Save Everyone”, as well as other posts about BCA tables from Lauren Stewart, Lowell Thomson, and Larry Dukerich.
In this blog post I'll describe a recent attempt at using BCA Tables for teaching stoichiometry. I discuss the method I used with one introductory chemistry class to teach both the algorithm method and BCA tables to learn more about a technique I've been curious about for a while.
A perfect storm starts to form. We are on the concept of moles and I have some students who are struggling mathematically. It is a rough time of year to get kids excited. Many students are struggling with ACT and SAT prep and as a teacher, I am tired of test...test...test. Also, I had about two dozen 2 liter bottle "pre forms" that I needed to find something to do with.
Stoichiometry is arguably one of the most difficult concepts for students to grasp in a general chemistry class. Stoichiometry requires students to synthesize their knowledge of moles, balanced equations and proportional reasoning to describe a process that is too small to see. Many times teachers default to an algorithmic approach to solving stoichiometry problems, which may prevent students from gaining a full conceptual understanding of the reaction they are describing.
There is a traditional stoichiometry lab I have done before. It involves adding dilute hydrochloric acid to sodium bicarbonate, boiling off the fluid and then getting the mass of the sodium chloride. Students then can solve the percent yield for the sodium chloride based on the amount of sodium bicarbonate they use. It is not a bad lab. Something about having hot ceramic watch glasses with acid just makes me a bit nervous. I am not sure where I got this new lab, but it has been one that has evolved over the years It is quick, dirty, relatively simple and uses over the counter (mostly) materials.