Acid Base Equilibrium
At a Glance
Discipline
- STEM
- Chemistry
Instructional Level
- University
Course
- Chem120 (General Chemistry 2)
Tasks in Workflow
Social Plane(s)
- Individual
- Group
Type of Tasks
- Solving problems
- Reviewing & assessing peers
- Reading
Technical Details
Useful Technologies
- Paper & Pencil
Class size
- Very Large (>250)
Time
- Single class period (< 90 mins)
Overview
In this activity, students problem solve and review their peers. In the first part, they learn how to apply Henderson-Hasselbalch equation (pH/pKa relation) by solving specific examples. In the second part, they have the opportunity to review the thinking of another group to identify potential misunderstandings and common mistakes. At the end of the class they get to answer one challenge question.
The instructor begins class with a lecture that follows the subject of previous two classes (basics on Acid-Base equilibria including acid-base definition, conjugate acid-base pairs, pH determination, acid-base strength, polyprotic acids, definition/application of pKa). The lecture covers Henderson-Hasselbalch equation, and provides a deeper explanation of how to apply the equation. The students apply their understanding to a biologically relevant molecule. They work in small groups to determine which ionization state of a polyprotic acid is most prominent at a particular pH.
With the help of the TA and instructor, the class is divided in groups of no more than 6 students each. Each group is given one of 8 distinct questions. Of the 8 questions there is a pair that relate to each of the four cases. Working on a shared paper, the students discuss to determine which case matches their problem. Once they decide, they work together to answer the question. Students will need around 10-15 minutes to determine the case and calculate the answer. They will determine the case that they are working on, and show their answer.
For the second part, the instructor and TAs help groups identify another group with a related question. Groups switch with one another to be able to review each other’s determination of the case and calculations. The activity ends with a class-wide review of the questions and answers by the instructor, and one challenge problem.
The instructor provides the questions and answers to students online for them to practice other cases.
Instructional Objectives
Students learn to…
- Apply Henderson-Hasselbalch equation to a biological system
- Understand the relevance of pH-pKa relations
- Determine the relation between acidic/basic components, and relate conjugate acid-base pairs
- Evaluate and assess peer’s work
Workflow & Materials
Activity Workflow
Contributor's Notes
Pallavi Sirjoosingh
McGill University, Montreal
- Improves students’ conceptual understanding of acids/bases and ability to solve problems.
- Provides students an opportunity to assess/evaluate other students’ work in a low stakes situation (no grade associated)
- Students can assess their understanding of a recently completed module in class.
- The switchover from writing the answers to grading them, may be difficult for larger classrooms. The instructors will need help from TAs to manage this.
- Students may not be familiar with peer assessment, and may not critically evaluate other student’ work or feel shy about being critical. The rubric should be clear and concise. Give examples on grading/assessment
- Time may be an issue
- This activity should be performed at a point in the course where students have become familiar with several concepts in equilibria (especially writing equilibrium constant for an equation).
- Students should have also completed a lecture that introduces them to basics of acid-base equilibria (Acid/base theories, Conjugate acid/base pairs, autoionization of water, and pH)
- It is highly recommended to have at least 1 TA for 6 groups.
Applied Strategies
Published: 26/01/2021
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