This lesson is part of a three-day lab. In the first day students design their lab, which includes solving a stoichiometry problem. On the second day they conduct the lab, and on the third day they write and critique their lab report.
In this third lesson students will use a Lab Report Rubric written by our science department to evaluate a stoichiometry lab report that they have already written.
This lesson aligns to the NGSS Disciplinary Core Idea of HS-PS1-7: use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction by asking students to demonstrate stoichiometry at the lab bench.
As such, it aligns to the NGSS Practice of the Scientist of Analyzing and interpreting data and Using mathematics and computational thinking because students must interpret and evaluate the data they collected from their lab. It also aligns with Obtaining, evaluating, and communicating information by affording students the opportunity to communicate their findings from the lab bench.
It aligns to the NGSS Crosscutting Concept of Changes of because this lab report illustrates how matter in a system can be described in terms of matter flows out of that system.
In terms of prior knowledge or skills, students in my class have already completed the Stoichiometry Lab as found in this lesson. At this point they should have a clear understanding of how to write a lab report and how to use stoichiometry.
There are no special materials needed for this lesson; however, students will use a word processor.
Do Now: I begin class by asking students to text code their lab report using letter number
combinations found on this rubric. For example, for each location where the student has answered a background question, she should write B2.
I reason that this is a good way to start class because I want students to evaluate their own lab report at the start of class because they will work on revising their lab reports in class today, and so when I
begin instruction they will already have spent some time thinking about the quality of their work.
Activator: I ask students to identify how many times they have written B2. My hope is that students have written this code three times—one for each of the background questions found in the lab report directions.
I have chosen this approach because the background questions are easily quantifiable, and this is pretty clear-cut example of how to answer the question, “Is your lab report complete?”
Mini-lesson: During this time I review the rubric and the lab report directions, starting with Part E—Data. (We have already spent time reviewing the first half of the lab report, in this lesson.)
During this lesson I am pointing to parts of the rubric and directions while I am explaining. I note that students should have a data table and a graph, and that both should have labels that denote units. I note that each should have a title that explains their purpose, and that the title should be labeled Figure 1, Figure 2, etc.
I note that the Analysis/Results section is where you try to make sense of your data. This can be accomplished by using a percent yield, and by discussing outliers. I expect students to create an average for their trials. I note that item 5 is not relevant to this lab because we are all doing different experiments. However, comparing results to theoretical yield does meet the goal of this item by giving students something with which to compare their results. We discuss significant figures; I remind students that their final answers should reflect the precision of the balance they used.
For the conclusion section I note that there are 4 conclusion questions. I note that in the analysis and conclusion section it asks that “discrepancies between data and known values or class averages are explained” while in the conclusion section it says “relevance of data is assessed by comparing results of experimenter to known values and/or class data sets.” I ask students what they think this means.
My hope is that students understand that the first mention of discrepancies is to name them, while the second mention’s goal is to determine if the discrepancies call into question the relevancy of the data.
This Critiquing the Lab Report summarizes some of the expectations I have for the final draft of the lab report.
This instructional choice reflects my experience in receiving lab reports. Many of the items in the rubric need to be explicitly taught and discussed. I will be use this first formal lab report of the year to set teaching goals for the rest of the year.
Student Activity: During this time students have the choice of working with a partner, critiquing each other’s work, or critiquing their own. I encourage them to critique a partner’s work because a fresh set of eyes will sometimes uncover mistakes that the author has repeatedly overlooked. After critiquing the work students are then tasked with revising their work.
I want students doing this revision work because I believe that they will become smarter about scientific practice. Specifically, I want them to really evaluate their data and make a conclusion based on how confident they are that their data is error-free because of the accuracy with which they conducted their experiment.
During this time I walk around the room answering questions. I can also use software to look at each students laptop screen as they write, and I can send them messages about what I am reading and about their progress.
To wrap this lesson up I ask students to share out some things that they have revised today in their lab report.
Ending class this way allows me to let students remind the class about what the expectations are for the lab report. This diversity of voices increases the likelihood that students will internalize the expectations; they often respond better to their peers.
The finished product can be seen in student work sample 1, student work sample 2 and student work sample 3. I was pleased with the format and most of the writing in this assignment. The one thing that I kicked myself for as I was reading the reports is how many times students made the claim that more carbon dioxide was produced than the stoichiometry predicted. This claim shows a certain lack of understanding about what a percent yield of more than 100% indicates. As I explained to students afterwards, this discrepancy more than likely indicates a measurement error rather than a break in natural law--you cannot get more of a product than the theoretical yield predicts.