Exploring Students’ Understanding of Acid/Base Buffers in a Laboratory Setting

Authors: Friesen, Katherine A; Ghodsian, Roghaieh; Turov, Yevgeniya
Contact: Katherine Friesen: kfriesen@uwlax.edu
Course Name: General Chemistry II Laboratory

Course Description:
General Chemistry II (CHM 104) is the 2nd course in a two semester sequence of introductory chemistry. It is a mandatory course for students who are required to have one year of chemistry in their program. Students typically complete the General Chemistry I (CHM 103) and II sequence in the first two semesters of their freshman year if they meet the math prerequisite. CHM 104 significantly broadens student understanding of fundamental chemistry concepts and, unlike CHM 103, builds on topics throughout the semester. As a result, students often have difficulty with the course since a misunderstanding can carry through to multiple topics. Students also often have difficulty connecting material they learn in lecture with the hands-on experiments they perform in the laboratory, especially related to the equilibrium and acids/bases chapters. This lesson study focuses on the CHM 104 course’s 6th laboratory experiment, Acids and Bases II: Preparing and Using a pH Buffered Solution, which is the second experiment dealing with acid/base chemistry. Experiment 6 is preceded by an introductory lab to acids and bases that was featured in a previous lesson study undertaken by Drs. Turov and Friesen along with colleagues Dr. Melissa Anderson and Dr. Nadia Carmosini and is followed by an experiment that explores acid/base titrations.

After the successful redevelopment of Experiment 5 in a previous lesson study, it gave us the opportunity to revisit the next experiment in this acid/base series and work on improving student understanding of buffers, a challenging topic for most students in CHM 104. Though students are usually able to complete the relevant calculations for buffers in lecture, they generally are lost in a laboratory setting when they need to perform the relevant calculations and actually prepare a buffer on their own. A significant portion of the laboratory period is spent on describing buffer preparation and calculations; however, students still seem confused by the procedure and need quite a bit of assistance with the calculations. For this lesson study, we have prepared pre-lab videos that showcase the preparation of the buffer and also streamlined the experiment to only focus on one type of buffer system, which has helped shorten the pre-lab lecture and alleviated some confusion about preparation. We also found that a modified data sheet allowed the students to guide themselves through the calculations and also helped them relate their thought process to the material they learned in lecture. We are still working on ways to help students bridge the gap between experiment and calculation.

Exploring Students’ Understanding of Acid/Base Buffers in a Laboratory Setting Final Report