Exploring The Impact of Increased Acid Levels in Ocean Waters on Coral

Dharshi Bopegedera, The Evergreen State College

Summary

In this experiment students will explore the impact of increased acidity of ocean waters on corals. It is designed to use the chemistry concepts and lab techniques learned earlier in the academic year to explore an important problem scientists are trying to understand and solve. The "big idea" in sustainability is the impact of acidification of oceans on marine life and "big ideas" in chemistry are acid/base chemistry, stoichiometry, pH, and the relationship between pH and acid concentration. Lab techniques such as using an analytical balance, calibrating and using a pH meter, and preparing solutions of desired concentrations are involved. Students will use Microsoft Excel for recording, analyzing, and graphing of data.

Learning Goals

The goal of this laboratory is to help students understand that burning fossil fuels, which results in an increase in the acidity of ocean waters, has a detrimental impact on marine life (specifically coral but also other organisms that have calcium carbonate based shells).

In completing this work students will use the "big ideas" in chemistry they learned in the classroom combined with the laboratory techniques to quantitatively investigate a 'big idea" in sustainability.

The "big idea" in sustainability is the impact of acidification of oceans on marine life and "big ideas" in chemistry are acid/base chemistry, stoichiometry, pH, and the relationship between pH and acid concentration.

It is hoped that by doing this work, students will recognize that the decisions they make in their lives have an impact on other organisms on earth. Students will re-visit many of the chemistry concepts and laboratory techniques they learned earlier in the year which will help strengthen these concepts and skills.

Context for Use

This lab is designed to take place towards the middle of the academic year in a three-quarter or two-semester general chemistry sequence. It will take one lecture period and two lab periods of three hours each. In addition, students will spend time outside of class on the library assignment, analysis of data, and writing the lab report.

Possible Use in Other Courses: This lab could also be conducted in an environmental chemistry course.

Description and Teaching Materials

The Learning Activities

To help set the stage, each group of students (3 or 4 students per group) will be directed to the campus library to find an article from a book or a peer reviewed journal on ocean acidification and its impact on marine life. They will study this article and write a short summary.

Each group will share their information in short oral reports with their peers during lecture. They will provide copies of their article to the rest of the class (or put articles on a Web site for easy access for other students) and take notes of others' presentations. These articles will be used later when students write their formal lab reports.

Students will then conduct an experiment in the lab to determine the change in the amount of calcium carbonate in coral samples after being exposed to various levels of acidity. Calcite will be substituted for coral (since calcite is easy to find than coral and the main chemical in both materials is calcium carbonate).

During the first lab period, students will prepare the acid solutions of desired concentrations, determine their pH, weigh out the calcite samples with an analytical balance, and place them in the labeled acid solutions. The samples will sit in acid for one week. During the second lab period, the acid solutions will be drained and disposed properly, the beakers rinsed clean with DI water, the calcite samples dried in an oven, cooled, and weighed using an analytical balance.

As post lab work, students will input their lab data into a Microsoft Excel Spreadsheet and calculate the change in weight of each of the calcite samples. They will then calculate the amount of calcium carbonate lost per gram of calcite and graphically plot this information as a function of pH using Microsoft Excel. They will look for any visible trends in their data. The results of this experiment will be written as a formal lab report and a discussion on the health of marine life in the face of increased acidity of oceans (using the articles collected earlier in the library and presented in lecture) will be included as a part of this report. Students will be directed to recognize that their experiment represents a "closed system" compared to the ocean which is an "open system." A statement comparing these two systems will also be included in the report.
Students can be further encouraged to present their results to another class, a student club, in the dorms, at a local school, or at a science fair so they can educate others.
  • Library Assignment: Students collect articles from the campus library (from a book or a peer reviewed journal) on the impact of an increase in the acidity of ocean waters on the health of marine life and then write short summaries of the articles. Lecture Discussion: Students bring copies of the article for the entire class (or put articles on a website for easy access for other students), and give a short oral report on the article to the class. Students take notes on their peers' presentations.
  • Lab Work:Over two lab periods, students conduct the experiment in pairs, gather data, write reports (individually) incorporating lab data, and present their results in the context of the lecture discussion on the impact of acid rain on the health of marine life. To this report, students attach the article they collected, the annotated bibliography, and notes taken in class during the discussion.
  • Presentation of Lab Work: If possible provide an avenue for students to present their lab work to another class, in the dorms, to a student club, a local school, or at a science fair.

Teaching Notes and Tips

The amount of calcium carbonate in calcite could also be determined using a back titration (for an honors chemistry course).

Assessment

The instructor will evaluate the lab reports, the summaries of the articles, and notes taken in class during the lecture discussion.

References and Resources

The campus library will be used as a resource. Students can also be connected to the EPA web site on acid rain at http://www.epa.gov/acidrain/ for further information.

Evergreen State College