Unit Overview
C.4 Chemical Reactions in our World

Why are oysters dying, and how can we use chemistry to protect them?

Unit Summary

Why are oysters dying, and how can we use chemistry to protect them? This unit is designed to build a deeper understanding about chemical reactions by exploring reversible reactions through exploration of ocean acidification. Students watch case videos, analyze data, and read about how movement of carbon dioxide from the atmosphere to the ocean makes the ocean more acidic. They consider how oyster die-offs may affect communities that rely on oysters for a food source. Students break down this large scale problem into a few key subproblems so they can use chemistry to try to solve them. They figure out how changes in concentration of H+ ions in water leads to changes in water pH. They use their knowledge of chemical reactions and mathematical thinking (stoichiometry) to determine the amounts of a substance they could use to neutralize acidic water. Students consider engineering trade-offs, criteria, and constraints to use chemistry to develop a design solution at a specific site to address oyster die-offs. They apply their thinking in a culminating task around increasing rates of ammonia fertilizer.

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Additional Unit Information

Building Toward the Following Standards and Practices
Performance Expectations

This unit builds toward these performance expectations:

  • HS-ESS2-6† Develop a quantitative model to describe the cycling of carbon among the hydrosphere, atmosphere, geosphere, and biosphere.
  • HS-ESS3-4* Evaluate or refine a technological solution that reduces impacts of human activities on natural systems.
  • HS-ETS1-1* Analyze a major global challenge to specify qualitative and quantitative criteria and constraints for solutions that account for societal needs and wants.
  • HS-ETS1-2† Design a solution to a complex real-world problem by breaking it down into smaller, more manageable problems that can be solved through engineering.
  • HS-PS1-5 Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.
  • HS-PS1-6 Refine the design of a chemical system by specifying a change in conditions that would produce increased amounts of products at equilibrium.
  • HS-PS1-7 Use mathematical representations to support the claim  that atoms, and therefore mass, are conserved during a chemical reaction.

*This performance expectation is developed across multiple units.

†This performance expectation is developed across multiple courses.

Disciplinary Core Ideas

PS2.B: Types of Interactions

  • Chemical processes, their rates, and whether or not energy is stored or released can be understood in terms of the collisions of molecules and the rearrangements of atoms into new molecules, with consequent changes in the sum of all bond energies in the set of molecules that are matched by changes in kinetic energy. 
  • In many situations, a dynamic and condition-dependent balance between a reaction and the reverse reaction determines the numbers of all types of molecules present.
  • The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

ESS2.D: Weather and Climate

  • Changes in the atmosphere due to human activity have increased carbon dioxide concentrations and thus affect climate.

ESS3.C: Earth and Human Activity

  • Scientists and engineers can make major contributions by developing technologies that produce less pollution and waste and that preclude ecosystem degradation.

ETS1.A: Defining and Delimiting Engineering Problems

  • Criteria and constraints also include satisfying any requirements set by society, such as taking issues of risk mitigation into account, and they should be quantified to the extent possible and stated in such a way that one can tell if a given design meets them.

ETS1.B: Developing Possible Solutions

  • When evaluating solutions, it is important to take into account a range of constraints, including cost, safety, reliability, and aesthetics, and to consider social, cultural, and environmental impacts.

ETS1.C: Optimizing the Design Solution

  • Criteria may need to be broken down into simpler ones that can be approached systematically, and decisions about the priority of certain criteria over others (tradeoffs) may be needed.
Focal Science & Engineering Practices

This unit intentionally develops students’ engagement in these practice elements:

Asking Questions and Defining Problems

  • 1.2 Ask questions that arise from examining models or a theory, to clarify and/or seek additional information and relationships.
  • 1.8 Define a design problem that involves the development of a process or system with interacting components and criteria and constraints that may include social, technical, and/or environmental considerations

Using Mathematics and Computational Thinking

  • 5.1 Create and/or revise a computational model or simulation of a phenomenon, designed device, process, or system.  
  • 5.2 Use mathematical, computational, and/or algorithmic representations of phenomena or design solutions to describe and/or support claims and/or explanations.  
  • 5.5 Apply ratios, rates, percentages, and unit conversions in the context of complicated measurement problems involving quantities with derived or compound units (such as mg/mL, kg/m3 , acre-feet, etc.).


The following practices are also key to the sensemaking in this unit:

Developing and Using Models

  • 2.2 Design a test of a model to ascertain its reliability.
  • 2.3 Develop, revise, and/or use a model based on evidence to illustrate and/or predict the relationships between systems or between components of a system.  
  • 2.4 Develop and/or use multiple types of models to provide mechanistic accounts and/or predict phenomena, and move flexibly between model types based on merits and limitations.
  • 2.6 Develop and/or use a model (including mathematical and computational) to generate data to support explanations, predict phenomena, analyze systems, and/or solve problems.

Planning and Carrying Out Investigations

  • 3.1 Plan an investigation or test a design individually and collaboratively to produce data to serve as the basis for evidence as part of building and revising models, supporting explanations for phenomena, or testing solutions to problems. Consider possible confounding variables or effects and evaluate the investigation’s design to ensure variables are controlled.  
  • 3.6 Manipulate variables and collect data about a complex model of a proposed process or system to identify failure points or improve performance relative to criteria for success or other variables.

Constructing Explanations and Designing Solutions

  • 6.3 Apply scientific ideas, principles, and/or evidence to provide an explanation of phenomena and solve design problems, taking into account possible unanticipated effects.
  • 6.5 Design, evaluate, and/or refine a solution to a complex real-world problem, based on scientific knowledge, student-generated sources of evidence, prioritized criteria, and tradeoff considerations.

Engaging in Argument from Evidence

  • 7.1 Compare and evaluate competing arguments or design solutions in light of currently accepted explanations, new evidence, limitations (e.g., trade-offs), constraints, and ethical issues.  
  • 7.4 Construct, use, and/or present an oral and written argument or counter-arguments based on data and evidence.
  • 7.5 Make and defend a claim based on evidence about the natural world or the effectiveness of a design solution that reflects scientific knowledge and student-generated evidence.
  • 7.6 Evaluate competing design solutions to a real-world problem based on scientific ideas and principles, empirical evidence, and/or logical arguments regarding relevant factors (e.g. economic, societal, environmental, ethical considerations).
Focal Crosscutting Concepts

This unit intentionally develops students’ engagement in these practice elements:

Cause and Effect

  • 2.1 Empirical evidence is required to differentiate between cause and correlation and make claims about specific causes and effects.
  • 2.2 Cause and effect relationships can be suggested and predicted for complex natural and human designed systems by examining what is known about smaller scale mechanisms within the system.
  • 2.3 Systems can be designed to cause a desired effect.

Scale, Proportion, and Quantity

  • 3.1 The significance of a phenomenon is dependent on the scale, proportion, and quantity at which it occurs.
  • 3.3 Patterns observable at one scale may not be observable or exist at other scales.
  • 3.4 Using the concept of orders of magnitude allows one to understand how a model at one scale relates to a model at another scale.

Stability and Change

  • 7.1 Much of science deals with constructing explanations of how things change and how they remain stable.
  • 7.2 Change and rates of change can be quantified and modeled over very short or very long periods of time. Some system changes are irreversible.
  • 7.4 Systems can be designed for greater or lesser stability.

This unit does not claim any crosscutting concepts as key to sensemaking.

Connections to the Nature of Science

Which elements of NOS are developed in the unit?

  • Scientific Knowledge Assumes an Order and Consistency in Natural Systems: Science assumes the universe is a vast single system in which basic laws are consistent. (HS-PS1-7)

How are they developed?

  • Students engage deeply with the idea that atoms and mass are conserved during a chemical reaction, especially using the mole for conversion from the atomic to the macroscopic scale. The unit emphasizes assessing students’ use of mathematical thinking, especially in Lessons 8, 9, 10, and 15.
Connections to Engineering, Technology and Applications of Science (ETS)

Which elements of ETS are developed in the unit?

  • Influence of Science, Engineering, and Technology on a Society and the Natural World:  New technologies can have deep impacts on society and the environment, including some that were not anticipated. Analysis of costs and benefits is a critical aspect of decisions about technology. (HS-ETS1-1)

How are they developed?

  • Students analyze a number of chemical engineering technologies for mitigating oyster die-offs and they include how these solutions may cause other problems in the larger ocean systems. They  analyze a number of costs and benefits to several interested groups.
Unit Information
Where does this unit fall within the OpenSciEd Scope and Sequence?

This unit is the fourth in the OpenSciEd High School Chemistry course sequence, and it is designed to build on previously developed understanding about kinetic molecular theory and patterns in how elements react to apply these ideas to oyster larvae die-offs due to ocean acidification. Four of the Performance Expectations (PEs) in this unit are shared across other units and across OpenSciEd High School Biology B.2.

  • ESS3-4 and ETS1-1 are shared with OpenSciEd Unit C.5: Which fuels should we design our next generation vehicles to use? (Fuels Unit).
  • ESS2-6 and ETS1-2 are shared with b2 OpenSciEd Unit B.2: What causes fires in ecosystems to burn and how should we manage them? (Fires Unit).


In the first unit of OpenSciEd HS Chemistry, students developed ideas around kinetic molecular theory in the context of polar ice melt due to global climate change from increased atmospheric carbon dioxide causing sea level rise around the world. In the second unit of the course, the differential damage caused by lightning in different countries motivated the need for students to build a detailed explanation of how charge (in the form of subatomic particles called electrons) moves between objects. In the third unit of the course, students used the search for another world for human habitation and the  unique properties of water as a context to investigate subatomic structures and identify patterns in how different elements interact in different ways. This fourth unit pushes students to bring together different strains related to kinetic molecular theory and patterns in elements’ interactions and apply them to the new situation of combatting the effects of another problem created by humans pumping carbon dioxide into the atmosphere – ocean acidification. This engineering context necessitates the use of stoichiometry to quantify and track matter, quantification of how much carbon is moving between Earth’s systems, and careful consideration of how reversible reactions and differing reaction rates work at the particle level.

What is the anchoring phenomenon and why was it chosen?

For the anchoring phenomenon, students use the novel phenomenon of oyster larvae die-offs, overnight events that became widespread in the Pacific Northwest in the mid-2000s as ocean pH reached a new low in that area. Ocean acidification causing larvae die-offs provides the context in which to investigate acids and bases, reversible reactions and chemical equilibria, stoichiometry, reaction rates, carbon’s movement through Earth’s systems, and how people can apply ideas from chemistry and Earth science to decrease the effects of ocean acidification on oysters.


Ocean acidification’s effect on oysters was chosen for this unit after examining previously collected student interest data and consulting with our state advisory panel.

How is the unit structured?

The unit is organized into three main lesson sets. Lesson Set 1 (Lessons 1-6) focus on developing science ideas about acids and bases, how ocean acidification occurs, and an introduction to reversible reactions. In this Lesson Set we begin using our progress tracker to organize our thinking and identify possible solutions to help protect oysters Lesson Set 2 (Lessons 7-10) shifts the focus to determining how we can quantify substances using stoichiometry and how we specifically intervene to promote shell formation in oyster larvae.  Lesson Set 3 (Lessons 11-14) shifts the focus to better clarifying criteria and constraints and applying our learning to develop solutions that will help oysters in specific situations. Students apply these ideas in a transfer task in Lesson 14.

What modifications will I need to make if this unit is taught out of sequence?

This is the fourth unit of the High School Chemistry Course in the OpenSciEd Scope and Sequence. Given this placement, several modifications would need to be made if teaching chemistry before biology, or teaching this unit earlier in the Chemistry course. These include the following adjustments:

  • If taught before OpenSciEd High School Biology, supplemental teaching of carbon cycling due to photosynthesis, respiration, and decomposition will be required.
  • If taught earlier in the school year, supplemental teaching of the kinetic theory of matter, ionic bonding and balancing chemical equations may be required.
  • If taught as part of an AP Chemistry course, be prepared to provide students with additional support around rate laws, reaction mechanisms, catalysis, equilibrium constants and solubility equilibria, calculation of pH/pOH/pKa, and properties of buffers.
  • If this unit is taught before OpenSciEd Unit C.1: How can we slow the flow of energy on Earth to protect vulnerable coastal communities? (Polar Ice Unit), consider using lesson set 1 from C.1 Polar Ice before you begin this unit in order to establish anthropogenic climate change.
How do I shorten or condense the unit if needed? How can I extend the unit if needed?

We recommend allocating time so that the entire course can be taught. Depending on your priorities for physical and earth and space science, you may condense and focus students on the following parts. If you condense the unit, you will lose important sensemaking for students.

  • Lessons 1-8 focus on acid-base interactions (especially HS-PS1-5 and HS-PS1-6).
  • Lessons 6-10 focus on stoichiometry and reversible reactions and equilibrium (especially HS-PS1-7). This is where key components of water chemical engineering occur when the  “what is killing oysters” question gets answered.
  • Lesson 11-15 focuses on balancing the needs of interested parties in solving a difficult chemical engineering problem (ETS1-1, ETS1-2, and ETS1-3).

To extend or enhance the unit, consider following all lesson extensions

  • A number of lessons have extension opportunities and alternate activities. See lessons 4, 5, 10, 11, and 15 for built-in extensions.
  • Spend more time on carbon cycle thinking and sequestration, building from storing carbon in rocks in Lesson 13. You could accomplish a number of DCI-related objectives related to PS and ESS and ETS thinking, especially in the context of an Earth Science course or focus. A carbon sequestration focus could lead into C.5 Fuels unit coherently.
  • Investigate how pH levels fluctuate in the natural world, such as in aquariums, soil, or in other living things, beyond what is presented in Lesson 4 Home Learning.

Additional guidance for extensions are given within each teacher guide. There are several throughout the unit.

Unit Acknowledgements
Unit Development Team
  • Nicole Vick, Revision Unit Co-Lead, Northwestern University
  • Kerri Wingert, Revision Unit Co-Lead, University of Colorado Boulder
  • Dan Voss, Field Test Unit Lead, Northwestern University
  • Melissa Campanella, Writer, University of Colorado Boulder 
  • Michael Novak, Writer, Northwestern University
  • Kathryn Ribay, Writer, Stanford University 
  • Michelle Zhang, Writer, Oak Park & River Forest HS District 200
  • Imani Black, Science Advisor, Minorities in Aquaculture
  • Elizabeth Moses, Science Advisor
  • Alana Quintasket, Science Advisor, Swinomish Tribal Community
  • Ann Rivet, Advisor on ESS Integration, Teachers College Columbia University
  • Stuart Thomas, Science Advisor, Swinomish Tribal Community
Production Team
  • Madison Hammer, Production Manager, University of Colorado Boulder
  • Erin Howe, Project Manager, University of Colorado Boulder
  • Stephanie Roberts, Copy Editor, Beehive Editing
Unit External Evaluation
NextGenScience’s Science Peer Review Panel

An integral component of OpenSciEd’s development process is external validation of alignment to the Next Generation Science Standards by NextGenScience’s Science Peer Review Panel using the EQuIP Rubric for Science. We are proud that this unit has earned the highest score available and has been awarded the NGSS Design Badge. You can find additional information about the EQuIP rubric and the peer review process at the nextgenscience.org website.