Exploring the Connection between Atmospheric Carbon Dioxide and Ocean Acidification through a Python Coding Exercise

Human-driven carbon emissions have resulted in increased levels of dissolved carbon dioxide in the Earth’s oceans. This dissolved carbon dioxide reacts with water to form carbonic acid, which impacts ocean acidity as well as the solubility of carbonate-containing compounds, with far-reaching impacts on marine ecosystems and the human communities that depend on them. Exploring these connected chemical processes offers a rich opportunity to connect chemistry to current environmental issues while illustrating how to quantitatively approach equilibrium in complex chemical systems. Generally, nonlinear algebraic methods are used to determine the equilibrium concentrations of chemical species in systems with multiple equilibrium processes. Because these methods are cumbersome to solve manually and may be unfamiliar to chemistry students, we designed an activity that introduces students to the use of Python coding for solving systems of nonlinear equations. Students wrote code to calculate pH as a function of PCO2 in a freshwater system and compared their Python calculations to experimental pH measurements made on a system of deionized water pressurized with carbon dioxide. An instructor-supplied Python notebook in Google Colaboratory enabled students to further their learning by exploring the effect of PCO2 on model marine systems in which temperature, salinity, and calcium carbonate were added as variables. To support adoption of the Python notebooks for students and instructors with differing levels of coding experience, we provide multiple stand-alone resources that teach the basic coding tools needed to solve equilibrium problems.