Introduction to Carbonate Equilibrium
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The activity asks students to make observations about what occurs when two effervescent antacid tablets are placed into a beaker of water. The Students work together in groups. There are three parts to the activity. In the first part, the tablets are dropped into tap water and student groups (2-4 students) must complete a series of question sheets (one per group) that guide them through thinking about the event. In the second part, a presentation on chemical equilibrium for the carbonate system is given. The starting point is the answers received in the first part. Basic chemical reactions for the carbonate system are presented including equilibrium expressions for each reaction and discussion about open and closed systems. At the end of class, a handout is given to the students. In the third part, three beakers (acidic, neutral and basic solutions, but not indicated) are placed together and two tablets are placed into each beaker. Students are split into two groups (8-12 students) and are asked to describe why the reactions are different. Discussion follows collection of student responses in each part. Once the chemical reactions and equilibrium expressions are presented, they are involved and referenced in all discussions.
The class is an introduction to fundamental physical and chemical Earth processes for environmental science and geology majors. Students "should" have taken physical geology and chemistry I, and they "should" be enrolled in chemistry II.
Skills and concepts that students must have mastered
Students should have a basic understanding of chemical reactions and equilibrium.
How the activity is situated in the course
The course is team-taught and includes 2 one-hour lectures and a two-hour lab per week. The exercise is presented as part of the lab section during the start of the second half of the semester. It serves as the transition point from rocks and minerals to the carbonate system.
Content/concepts goals for this activity
The main content/concept goal of this exercise is to get students thinking about chemical equilibrium and the carbonate system.
Higher order thinking skills goals for this activity
The main higher order thinking goal for this exercise is for the student to understand the importance of pH and the distribution of carbonate species between the gas, aqueous and solid phases as a function of pH.
Other skills goals for this activity
Other skills goals include making and recording observations of an event, working in both small and larger groups. In addition, one student in each group must summarize the findings to the class. The majority of the students will be required to take a geochemistry class in two years. The discussion of chemical equilibrium in an environmental system lays the groundwork for this class.
Description and Teaching Materials
Teaching Notes and Tips
No introduction is provided prior to the start of the exercise. In the first part, students are placed into groups and the tables are dropped into the beaker. Brakers, water and tables are distributed to each group (2-4 students). Students place the tablets into the water and are asked to observe the reaction. The first page of "Group Questions for Introduction to Carbonate Equilibrium" is distributed. Students are given 5-10 minutes to complete. Once complete the sheets are collected and page 2 is given out. Students are given 5-10 minutes again. The sheets are collected and the third sheet is handed out and students are given 5-10 minutes to complete it.
Once the three sheets are collected a presentation on the carbonate system is given. See "Student Handout for Introduction to Carbonate Equilibrium" for overview. The handout is not given out till the end of class. In the third part, three beakers (acidic, neutral and basic solutions, but not indicated) are placed together and two tablets are placed into each beaker. Students are split into two groups (8-12 students) and are asked to describe why the reactions are different. Discussion follows collection of student responses in each part. Once the chemical reactions and equilibrium expressions are presented, they are involved and referenced in all discussions.
Active participation during discussion
References and Resources