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. And on a side note, I have put in an order for Argument-Driven Chemistry as well. I can't wait to delve into the labs offered there.
First, some background that might provide context and food for thought. The students in my HL Chemistry class generally have had a year of introductory chemistry in grades 9 and/or 10 that includes the mole and stoichiometry. Our stoichiometry lab in the introductory course is a bit more "cookbook" but it's still a lab I like. (Copy below within the resources.) It asks the students to calculate along the way, and I really enjoy hearing the students comment about how close their product mass is to their stoichiometric prediction. It has value in that part of the curriculum for my students.
But for my IB Chemistry students, I'm always looking to challenge them - and Ben's stoichiometry lab did just that. But before the stoichiometry lab, I had the classic "Empirical Formula of Magnesium Oxide" lab. I even modified this one from the typical cookbook to something a bit more student-designed. (Copy below within the resources.).This alone was a nice improvement over the previous cookbook, as the new method forced students to consider what data they needed to collect in order to answer the main question of the lab. Please note that even with student-driven investigations, I still talk about safety before every lab. It might give away some details about methods - but I typically give them time to discuss their plans before my safety discussion.
For stoichiometry, I used a modified version of Ben Meacham's stoichiometry lab (Copy below within the resources.). So how did it go? Fantastically, I would say. I won't rehash the way to work the lab - as Ben's post did such a fantastic job of that. Instead, I will share some feedback - and offer yet another round of encouragement for Argument-Driven Inquiry and the Claim-Evidence-Reasoning model of investigation. (I discussed using CER in a previous blog post as well.)
There were a few benefits to this lab. One such benefit is that the students were forced to make qualitative observations in order to solve the problem presented to them. I find qualitative observations often very lacking from students - and think this is partly my fault for not discussing them enough. With this lab, it is near impossible to accomplish the outcome without qualitative observations. And the sequence of the MgO lab - where qualitative observations were critical for evaluating the outcome - proved quite beneficial as well.
And for almost every group, the qualitative observations eliminated reaction 1 and 4 as possibilities right away. Which meant reaction 2 and 3 required quantitative measurements to verify. YEAH! This stumped a few groups, as they struggled to decide where to go. FANTASTIC! This lead to a nice discussion about gravimetric analysis and how it can be used in this setting - and others.
A number of students commented on how they liked the challenge of finding the reaction - rather than the simple cookbook labs they are familiar with. This has inspired me to modify my gas laws a bit as well (discussion coming in a future blog post). The main idea for me is getting students to be creative and think their way through a method that will collect the data needed to answer the research question. And I certainly still occasionally use a cookbook lab where efficiency is needed.
What have you done as modifications to your stoichiometry labs? (Or other labs, for that matter?) Do you see a benefit?
*Looks like I wasn't the only one inspired by Ben's post. Chad Husting has a recent post about his experience with this for a mole lab.
