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Investigating Ocean and Marine Algae Mark as Favorite (3 Favorites)

LESSON PLAN in Solubility, pH. Last updated April 14, 2023.


In this lesson, students will learn about coccolithophores, unicellular marine algae that inhabit the upper layer of the ocean. These phytoplankton form calcium carbonate, calcite, scales called coccoliths and are the biggest calcite producers in the ocean. First, students will observe photos of algal blooms of different types and analyze the photos for similarities and differences. Next, students will be introduced to types of marine algae including coccolithophores and to how ocean pH changes are impacting the availability of carbonate for use in the formation of calcite shells and coccoliths. Students will then plan and carry out a small-scale laboratory to investigate the relationship between the solubility of calcium carbonate and pH. To conclude, students will read an abstract of recent research into coccolithophores and ocean acidification and compare and contrast those findings with their own investigation’s results.

Grade Level

High school

NGSS Alignment

This lesson will help prepare your students to meet the performance expectations in the following standards:

  • 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-ESS3-5: Analyze geoscience data and the results from global climate models to make an evidence-based forecast of the current rate of global or regional climate change and associated future impacts to Earth systems.
  • Scientific and Engineering Practices:
    • Analyzing and Interpreting Data
    • Planning and Carrying Out Investigations
    • Constructing Explanations and Designing Solutions


By the end of this lesson, students should be able to:

  • Describe coccolithophores as marine algae.
  • Explain the impact of ocean acidification on the relative levels of carbonate ions, bicarbonate ions, and carbonic acid in the ocean.
  • Predict how changes in pH will impact the solubility of calcium carbonate.
  • Explain how the availability of carbonate in the ocean could negatively impact calcite forming organisms such as coccolithophores.

Chemistry Topics

This lesson supports students’ understanding of:

  • Solutions
  • Solubility
  • Solubility Equilibrium
  • Acids
  • pH
  • Chemical Reactions


Teacher Preparation: 60 minutes
Lesson: 90-120 minutes

Materials (per group)

  • 4-6 pieces of Marble Chips
  • 5 mL Vinegar
  • Well-plate
  • 2 Pipettes
  • Balance
  • pH paper (broad scale paper)
  • Water
  • Optional: A drying oven or method of drying samples would be beneficial


  • Reference the SDS for Calcium Carbonate
  • Reference the SDS for Vinegar
  • Always wear safety goggles when handling chemicals in the lab.
  • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
  • Students should wash their hands thoroughly before leaving the lab.
  • When working with acids, if any solution gets on students’ skin, they should immediately alert you and thoroughly flush their skin with water.

Teacher Notes

  • Students should work in groups of 2 to 4 depending upon the size of the class and available resources.
  • Calcium carbonate powder or small limestone pebbles could be substituted for the marble chips. If substituting, be sure that the pebbles are small enough to fit into the well plates.
  • Small cups or beakers could substitute for the well plates.
  • Dropper bottles could substitute for the pipets.


  • The term “marine algae” is used to describe a diverse group of eukaryotic organisms that engage in photosynthesis.
  • The types of marine algae include green algae, red algae, brown algae, golden algae, and dinoflagellates. Coccolithophores and diatoms are often grouped into the golden algae category.
  • Algal blooms occur when algae or cyanobacteria grow at a rapid pace. They may appear like a film or layer on the surface of the ocean. The color and appearance of the bloom can vary depending upon the type of algae.
  • Coccolithophores are unicellular marine algae that live in the photic zone. These phytoplankton form small plates made of calcite across the surface of the cell that are called coccoliths. See The Magical World of Coccolithophores for SEM images of four different species of coccolithophores.

Figure 1. Image courtesy of the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

  • Coccolithophores contribute from 1 to 10% of the primary productivity at the ocean’s surface.
  • They are also the largest producer of calcite sediment in the ocean, serving as a critical means for carbon sequestration as calcite.
  • When coccolithophores form an algal bloom, it often appears to be cloudy white or pale blue in the water due to the coccoliths being shed. In the satellite imagery in Figure 1, the coccolithophore bloom has been denoted with a yellow arrow. White clouds in the atmosphere are obscuring some of the bloom. Other algae/phytoplankton would appear green, brown, or even red.
  • Ocean pH has decreased from approximately 8.25 to 8.14 since the 1750s. This is attributed to the increased concentration of carbon dioxide gas in the atmosphere due to the combustion of fossil fuels throughout the industrial revolution. The higher the concentration of carbon dioxide in the atmosphere, the more dissolved carbon dioxide exists in ocean water.
  • Ocean acidification reduces the availability of the carbonate ion in the ocean for organisms such as coccolithophores for use in the formation of calcite (calcium carbonate).
  • As pH decreases, a smaller percentage of inorganic carbon in the ocean is available as carbonate See Figure 2 below for the graph that depicts the relative quantities of carbonate, bicarbonate, and carbon dioxide at different pH levels.

Figure 2.Relationship between equilibrium carbon dioxide, bicarbonate, carbonate, and pH.

  • pH can impact the solubility of an insoluble or slightly soluble ionic solid if the compound contains the conjugate base of a weak acid. If the anion in the solid is basic, changes in pH can cause an increase or decrease of the solubility of the solid due to Le Chatelier’s Principle.

Classroom Management:

  • To shorten the activity, the minilab could be adapted so that each group conducts one trial and the data is collected and reported out on a classroom board for analysis and discussion.


  • Teachers may differentiate this activity by the level of inquiry used in the activity. Students needing additional assistance might be provided with a suggested procedure and data table.
  • Teachers may also differentiate the activity according to the level of equilibrium calculations used in the experiment. 2nd year chemistry students would be more able to perform solubility equilibrium calculations.

Helpful Links:


Halder, K. (2018, September 25). The Magical World of Coccolithophores. JOIDES Resolution. Retrieved March 7, 2023, from https://joidesresolution.org/t....

For the Student


An algal bloom occurs when algae or cyanobacteria grow very rapidly in one area of the ocean. This causes a layer of colored material to form on the surface of the water. The satellite image below in Figure 1 shows two algal blooms occurring in the Bering Strait between Alaska and Siberia.

Figure 1. Image provided by the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

  1. Study Figure 1 closely and see if you can identify the location of the two algal blooms on the surface of the ocean. Once you have found the two blooms, describe any similarities or differences between the algal blooms below:


Figure 2. Image of a coccolithophore taken with an SEM at San Francisco University by Ina Benner. Open source image

The bloom in the right of Figure 1 consists of marine algae called Coccolithophores. These are single-celled marine algae that engage in photosynthesis in the upper layers of the ocean. Coccolithophores form small plates called coccoliths. These tiny plates are made up of calcium carbonate, the same compound found in limestone or marble rocks. These algae dump their excess coccoliths into the ocean and are the biggest producers of solid calcium carbonate, calcite, in the ocean.

Prelab Questions

  1. Write a balanced chemical equation for the dissociation of calcium carbonate in water:
  2. According to the United States Environmental Protection Agency, the pH of the ocean has dropped from 8.2 to 8.1 since the start of the industrial revolution. Make a prediction as to how this increase in acidity in ocean water will change the solubility of calcium carbonate in water.
  3. Use Figure 3 to estimate the percentage of inorganic carbon in the ocean in the form of carbonate ion at:
    1. pH of 10?
    2. pH of 9?
    3. pH of 8?

Figure 3. Relationship between equilibrium CO2, bicarbonate, carbonate, and pH.

  1. As the availability of the carbonate ion in ocean water decreases, how might this impact ocean organisms, like coccolithophores, that form shells or other body parts out of solid calcium carbonate?
  2. Write a balanced chemical equation for the reaction between acetic acid, CH3COOH and calcium carbonate, CaCO3.


How does the pH of water change the solubility of calcium carbonate?

Materials (Per Group)

  • Marble Chips, 4 to 6 pieces
  • Vinegar, 5 mL
  • Well plate
  • Pipettes
  • Balance
  • pH paper
  • Water


  • Wear safety goggles when conducting this lab.
  • Wash hands with soap and water upon completion of the lab.
  • Dispose of any waste as directed by your teacher after completion of the lab.

Plan Your Investigation

  1. Develop a procedure to observe how the pH of water changes the solubility of calcium carbonate in water. You must use the materials provided in the list above.
  2. Determine the independent variable for your investigation:
  3. What is the dependent variable for the investigation?
  4. What is the control?
  5. What constants will be maintained?
  6. Develop and record a detailed procedure in the space provided below and create a labeled data table based upon the procedure. Show your plan to your teacher for approval before beginning your experiment.


Data Table

Data Analysis

  1. In what solution was the calcium carbonate sample the most soluble?
  2. In what solution was the calcium carbonate sample the least soluble?
  3. Can you use your data to make a general statement about how pH changes calcium carbonate solubility?
  4. What were the limitations of your experiment? Identify and discuss any possible sources of error.


Using the Claim, Evidence, Reasoning (CER) format, write a conclusion about how ocean acidification may impact organisms such as coccolithophores which have calcium carbonate body parts.

Extension Activity

Read the abstract of this recent study into coccolithophores’ response to ocean acidification and warming in the Mediterranean Sea. How did these researchers’ findings fit in with your own conclusion?