Using the pH Scale and Carbonic Acid Formation to Understand the Effect of Ocean Acidification on Organisms with Calcium Carbonate Shells.

This page authored by Richard Rueb, Clackamas Community College, based on an original activity by Sheila Alfsen, Linn Benton Community College.
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Initial Publication Date: March 31, 2014 | Reviewed: July 21, 2015


In this lab activity, students work with the pH scale and the reaction of carbon dioxide with water to understand how anthropogenic carbon dioxide causes ocean acidification. Next students use weight loss from shell pieces in solutions of different pH values to examine the effect of acidification on calcite dissolution. Then students graph atmospheric and oceanic carbon dioxide levels over time to see how the ocean is responding to increased levels of carbon dioxide in the atmosphere. Finally, students make predictions regarding how oceans might be affected by anthropogenic carbon dioxide.

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Learning Goals

The concepts students should learn from this activity are that there is a relationship between anthropogenic carbon dioxide and ocean acidification and that ocean acidification may have an effect on marine organisms with calcium carbonate shells. Higher-order thinking skills developed by this activity include analysis of experimental and graphical data and the critical thinking necessary to understand the relationship between human activities and marine life.

Context for Use

This activity is a lab intended for use in an introductory environmental science course for non-science majors at a community college. Class size is typically twenty-four students per lab. It is anticipated that this activity will take approximately two hours in each of two consecutive labs held one week apart. There is no special equipment necessary and there are no skills or concepts students should have already mastered before encountering this activity. This activity is integrated into the topic of air pollution. Other related topics covered in the same term include fossil fuel recovery and use and climate change.

Description and Teaching Materials

This activity is divided into five parts. Parts 1-3 are done in the first week, and parts 4 and 5 are done in the second week. In Part 1, students answer basic questions about the pH scale using a pH scale that includes the pH values of pure water, seawater and various household solutions. In Part 2, students blow into a solution of distilled water and bromothymol blue to observe the effect of adding carbon dioxide to water on its pH. In Part 3, students observe the effect of vinegar on a piece of chalk and then weigh shell pieces, place them in solutions at various pH values, and measure weight changes after one week in the solutions. In Part 4 students graph atmospheric and oceanic carbon dioxide concentrations over time to determine how the ocean is responding to increased atmospheric carbon dioxide levels. In Part 5, students read an online article and make predictions about the effects of anthropogenic carbon dioxide on the oceans.

Teaching Notes and Tips

The most likely area of confusion is why the pH value of a solution decreases as its acidity increases because most non-science majors have little background in either chemistry or math. Regarding safety, students should wear goggles, gloves and aprons when working with the solutions of different pH values.


The best assessment strategy for this activity is to make sure that students are able to correctly answer the questions asked in each of the parts of the activity.

References and Resources

The one web resource for this activity is, which is the article "Acid Ocean" written by Mark Floyd, assistant director of communications at Oregon State University, and published in Terra Magazine. Atmospheric carbon dioxide data is taken from readings at Mauna Loa by Earth System Research Laboratory (NOAA) and C. David Keeling (Scripps Institute of Oceanography). Oceanic carbon dioxide data is modified from a presentation by Burke Hales, associate professor of oceanographic and atmospheric sciences at Oregon State University, at a COSEE (Center for Ocean Sciences Education Excellence) workshop in July, 2010. The pH scale referred to is in Environmental Science by Botkin and Keller, 8th ed.