OCEAN Acidification
Contextualize
Ocean acidification offers a rich, relevant, and interesting context for introducing, exploring, and analyzing central concepts in chemistry like solubility in water, chemical equilibrium, and acid-base reactions using a systems thinking approach. It creates opportunities for discussing how physical and chemical interactions between chemical species produced during human activities induce changes in aquatic systems that affect living organisms and the communities that depend on them for their subsistence.
Focus
The following infographic depicts the systems in interaction analyzed during the lesson. CO2(g) in the atmosphere dissolves in water in oceans, lakes, and rivers, participating in chemical reactions that affect their pH. These changes affect the availability of substances required by aquatic organisms, in turn impacting human systems:
Define
Central Ideas
The physical and chemical interaction between atmospheric components and water in rivers, lakes, and oceans have major consequences for life below water.
Physical interactions (intermolecular forces) between water molecules and molecules of atmospheric components determine their solubility in liquid water.
Interactions between positive and negative centers in molecules can induce chemical transformations, such as the transfer of protons (H+) in acid-based reactions.
Acids and bases react with water via proton transfer and alter the concentration of H3O+ and OH- ions in solution (change the pH). The extent of these reactions is determined by the equilibrium constant for each process.
Chemical substances released into the atmosphere during human activities can react with water, alter its pH, and induce shifts in multiple chemical equilibria that affect living organisms.
Core Practices
Analyze data to infer patterns and correlations between the behaviors of relevant components and properties in interacting systems.
Develop and apply molecular models to predict and explain the outcome of physical and chemical interactions between components in the systems of interest.
Build explanations and generate arguments about the effects of human products and activities on aquatic systems in our planet.
Systems Thinking Skills
System Composition: Identify the chemical composition and properties of substances in the atmosphere and hydrosphere involved in ocean acidification.
System Structure: Explore and identify the physical and chemical interactions and relationships between substances involved in ocean acidification.
System Behavior: Infer the effects of different interactions on the properties and behavior of systems and subsystems affected by ocean acidification.
System Effects: Identify and analyze ocean acidification's effects on marine life and the communities that depend on them for subsistence.
Socio-environmental Competencies
Evaluate the environmental, economic, and social impact of human activities that lead to ocean acidification.
Design
The following presentation includes a sequence of content and activities for a proposed two-week lesson (approximately six 50-minute sessions) that engages students in the development and application of chemical systems thinking to the understanding of ocean acidification. The lesson is designed for an introductory general chemistry lecture course at the university level.
Ocean Acidification.pptxThis example lesson introduces and applies the following chemistry concepts: Dynamic physical and chemical equilibria, equilibrium constant, gas solubility, acids and bases (definition, strength, pH), and perturbations to chemical equilibria.
This example lesson assumes students already have a basic understanding of the particulate model of matter, molecular structure, polarity, intermolecular forces, and matter and energy transformations during chemical reactions.
The following diagram depicts a suggested schedule for the implementation of this example lesson:
The example lesson includes a set of interspersed activities (labeled "Let's Think") that students are expected to complete in small collaborative groups and then share their ideas in whole class discussions. These activities ask students to share and explore chemical concepts, actively engage in core science practices like analyzing data, making predictions, applying models, and generating explanations, and practice systems thinking skills. The specific system thinking skills that each activity may help foster are highlighted using representative icons. They also create opportunities for the instructor to formatively assess student learning and provide specific feedback to advance their understanding.
Map Out
During the "map out" phases of a lesson, students are introduced to the socioenvironmental problem under analysis to identify the systems in interaction. This phase should allow them to develop an overall view of the nature and complexity of the problem or phenomenon to be analyzed. As illustrated in the example lesson on ocean acidification, this can be accomplished by engaging students in analyzing relevant data that helps them identify major components, behaviors, patterns, or relationships we seek to understand during the lesson. These activities create a need to know and opportunities for students to activate and share prior knowledge and experiences related to the phenomenon. For example, consider this activity in the introductory "map out" phase of the example lesson where students are asked to analyze trends in atmospheric CO2, ocean CO2, and ocean pH and brainstorm ideas about their causes and effects:
Zoom In
During the "Zoom In" phases of a lesson, students engage in activities that help them identify the main components in the systems of interest, analyze their properties, and characterize their interactions at levels of granularity that are productive in making sense of the problem or phenomenon under consideration. In the example lesson on ocean acidification, students first explore physical interactions between atmospheric components and water in the hydrosphere at the molecular level, as illustrated by the following "Let's Think" activity:
In the second part of the lesson, students explore chemical interactions between components at various granularity levels, including the atomic and electronic levels as illustrated below:
Zoom Out
Once students model and understand the phenomena of interest at submicroscopic levels of granularity, it is important to "zoom out" using activities that help them recognize system-level properties and behaviors that emerge from the interactions between components. For example, in the proposed lesson on ocean acidification, students are asked to derive information about the directionality and extent of critical chemical processes once particulate-level mechanisms for chemical equilibria have been discussed and understood:
Students are also asked to predict and explain how different factors affect the properties and behaviors of the system using chemical mechanisms at the molecular level. Consider the following activity as an example:
Connect
In the "Connect" phases of the lesson, students engage in activities that allow them to explore the effects of interactions between relevant subsystems, as illustrated below:
As well as apply their knowledge in making decisions and suggesting or implementing individual or collective actions directed at addressing the societal and/or environmental problem under consideration:
Evaluate
The "Let's Think" activities interspersed in the example lesson create diverse opportunities to formatively assess student learning and provide specific feedback to advance their understanding to meet the lesson's learning objectives. These activities also help students evaluate strengths and areas needing improvement in their learning. As part of the summative assessment, we suggest implementing an activity that requires students to apply their understanding to analyze a different system of interest. This summative assessment could be completed individually or in small groups, inside or outside the classroom. An example of this type of summative assessment is included at the end of the example lesson as a "Let's Apply" (LA) activity focused on Acid Rain.
Reflect
During the implementation of the lesson, it is important to systematically gather information about student learning and performance that can help us critically reflect on aspects of the lesson that need to be modified to support student learning of the central ideas, core practices, and socio-environmental competencies targeted by the lesson.