Wednesday, 19 April 2017

Ocean Acidification Inquiry Activity (Grades 7-12)

Ocean Acidification Inquiry Activity (Grades 7-12)

An iceberg covered with gulls in Conception Bay, NL, Canada.


The first lesson I would like to post on my blog is an Ocean Acidification Activity. Ocean Acidification is a serious matter. Each year human combustion activities pump 50 million metric tonnes of carbon dioxide into the atmosphere (Schnoor, 2013). Carbon dioxide in the air dissolves freely into the oceans (Byrne, 2014, p. 5352) and this is creating problems with ocean chemistry (Schnoor, 2013). For the oceans, "the massive amount of CO2 absorbed, about 1 million tonnes per hour, generates large-scale changes in seawater chemistry that are collectively referred to as anthropogenic ocean acidification" (Gattuso, Mach, &  Morgan, 2013, p. 726). The acidification result from processes that convert carbon dioxide into carbonic acid (Byrne, 2014) and results in pH changes in the ocean (Schnoor, 2014; Schnoor, 2013).

Watch the video! 

Not many students are aware of the ocean facts related to this phenomenon:

1. If it were not for the sea's ability to absorb carbon dioxide the planet would likely be much warmer - thank you ocean! 
2. Carbon dioxide dissolves into the ocean and forms carbonic acid. 
3. The pH of the ocean is currently above pH 8. It was 8.2 but has decreased to 8.1, not acidic but becoming more acidic. Many studies suggest the pH of the ocean is decreasing (by 25% in the past 200 years).
4. The current level of pH of the ocean allows organisms to make shells using calcium carbonate (due to the low solubility of CaCO3 above pH 8). A decrease in pH diminishes some species ability to make their shells. Many of these organisms are the bottom of the food chains or base of ecosystem energy pyramids. 
5. If the pH of the ocean decreases many organisms will be impacted, and it may change the balance of the ecosystems in the oceans.
6. We are the cause of the problem. However, we are also the solution to this issue (keep it positive, we need students to help our oceans!).

The goal of the lesson is to help students make connections between the physical change in ocean water and the over production of carbon dioxide by burning fossil fuels. The trick to making the lesson "turn the tide" of realization of the human impacts on our planet. I suggest you start with a simple task – examining basic the pH of an ocean water sample and seashells. This will require two sessions, one to conduct activities and a second for evaluation and discussion. It is possible to piece together the events in another order: this is your choice, and I would be interested to hear how it goes (I love changing things up).  

Materials Required: 
1L of seawater or artificial seawater (see recipe*), 100 or 200 ml beakers, clean drinking straws, safety goggles, seashells (not snail shells and they must be free of allergens), Vinegar, Bleach, LabQuest2 with pH and CO2 probes, or Litmus paper (red and blue) or bromothymol blue solution (there are three different strategies to collect data for pH change). 

*If you have no access to seawater you can make a sample with tap water and table salt. A tested recipe is 1 teaspoon NaCl per 200 ml of tap water (this makes a sample of about 30-35 ppt). If you have some limewater you could add 30-40ml to the 200 ml of salt solution. The pH will not be 8 but the water should be alkaline (you may also raise the pH by adding drops of bleach until you get the pH you desire). Once you have your sample prepared and tested, set it aside until required.

Steps of the lesson (steps 1 and 2 may be switched):
  1. Break into lab groups and answer an information question related to the carbon cycle. The intention is to start a discussion about the problems of excess carbon dioxide.
  2. Introduce a discrepant event and use POE (follow this link for an explanation of POE -
  3. Use the discrepant event to make a connection to the ocean and have student lab groups conduct investigations that relate to the carbon problem.
  4. Students report their data to the class. Discuss how they results relate to the problem of CO2 levels and ecological changes on Earth. Class analysis and recommendations.
  5. Conduct an extension activity (another POE) and ask students to make recommendations based upon the results of the experiments. 

1. Group questions and examining the problem (10 minutes)
Start the class by breaking into lab groups and ask students to think about the carbon cycle. Pass out some seashells (make sure they are clean and dry, if not, students with shellfish allergies may react). My students will have investigated the cycles using the “mini-earth” (that is a later blog) so I remind them of the principles of cycling demonstrated by our previous investigations. Ask the student groups or lab groups one of these questions: 

What forms of carbon exist on the planet? 
What processes add carbon to the atmosphere? 
What processes remove carbon dioxide from the atmosphere? 
What is the Greenhouse Effect?
How are humans connected to the carbon cycle?
What is carbon storage? Name some examples (the seashell is one!)
These questions require 4-5 minutes to answer and have students post written answers on a wall for review by the whole class. This warm up is a good baseline level of discussion. Add the following to the discussion: “What do scientists believe is the cause of the Greenhouse Effect?” or  “What forms of evidence offered by scientists to support their assertions?”

This line of inquiry by lab groups may not lead to the idea of ocean acidification. Students should know they produce carbon dioxide and that it is able to dissolve in water. Next, you need to use some pH indicator magic to hook the students.

2. Discrepant Event (POE) (10 minutes)
Put 100 ml of your seawater sample into a beaker. Add bromothymol blue indicator (it should remain blue if the pH is 8, make sure you test it!). Tell the students what you seawater and then ask the student lab groups "What will happen if I blow bubbles in this beaker of seawater?" Allow them to record answers and predict, then demonstrate the process. As you slowly bubble air through the water the solution, the students will observe it turn blue-green then yellow. Ask the students, what happened and why? Since the class is full of oxygen, could it be oxygen? What else could it be? Nitrogen? In groups, suggest what gas caused this change? You must ask them, what will happen if we leave this beaker overnight? (this solution will turn blue overnight as the CO2 dissolves out of solution - you can observe this the next day).

Students may make the connection to an acid being formed. If not you can tell them seawater changed because of the carbon dioxide. When you exhale CO2 into water it forms carbonic acid and this acid reduces the pH of the water, making it more acidic. You could explain pH, but I prefer to let them conduct one of two experiments and the need for knowing pH will arise from their investigations.

3. Experiments with Seawater (20-30 minutes)

Ask the lab groups to conduct an experiment and report their findings to the class. There are two experiments: 1. Measuring the pH of seawater as CO2 is bubbled through it; 2. Exposing seashells to tap water, an acid, and a base. The experiments are complementary and it is useful to have different lab groups collect observations then pass them on the other groups (using a grouping strategy that has students going to other groups to report their group's results or by posting the results in some manner, such as on the wall again). 

Experiment 1 – Bubble experiment: Each lab groups, now called the bubble groups, must obtain a straw, goggles, a beaker, and a pH-measuring device (litmus paper, calibrated pH meter (LabQuest 2 with pH probe) or bromothymol blue indicator). Ask the student to devise a protocol to examine the change in acidity. Let them struggle with the procedure and report the steps to you before they start. They must consider safety and their data must include a baseline reading, time of the bubbling, and have a “bubbling protocol” (good science controls variables to isolate the one of interest – CO2 impact on pH). For example, they should take a baseline pH reading then bubble for thirty seconds, then record pH again. They should record the pH every 30 seconds and bubble for about 2-3 minutes (exhaling normally - no need to pass out!). The pH should drop by a whole unit on the pH scale or be noticeable with the Litmus paper. This is a great opportunity for them to examine the pH scale of pH and is an opportunity to explain the logarithmic scale as you travel around visiting the lab groups. Have the groups graph the data, pH versus time (or colour versus time), and prepare to report their results for next day.

While the students conduct this experiment connect the pH probe to the LabQuest2. Run an experiment overnight to graph the pH over 24 hours - acidity will give way to a pH of over 8 once the CO2 gases off!  

Experiment 2 – Seashell experiment: This experiment will examine the effect of pH on seashells. For the shell experiment lab groups, now called the shell groups, will use three beakers, three similar sized seashells, seawater solution, vinegar, bleach (diluted to 25%) and a balance for mass determination. Ask the students to determine the protocol for exposing shells to three different liquids; safety is important as they are handling acids and bases. Procedures should involve determining the initial mass of seashells and recording the result (the mass should be ± 0.01g if possible). Have students note the features of the shells (visual and tactile inspection); pictures are advised. The shells should be dropped into the respective solutions and observations documented. Again, circulate around the groups - a gas may be evolved, the solution may get cloudy, reinforce that all these observations are important. Ask the students to consider allowing the experiment to continue overnight (the reaction is not vigorous with a weak acid). If they do, at the beginning of the next class the must rinse the shells off with water, make visual observations, dry then and obtain the mass of each shell. The group must add the data to the prepared table to report their findings to the other groups. The ‘bubble groups’ could watch the shell groups finish their data collection and this is a time to explain procedures used by the shell groups.

4. Reporting the Findings (Next day, 20 minutes)
The student scientists now need to report their data. It is exciting to start with the results, then open the floor for the students to question each other in terms of procedures, safety considerations and standardization of measuring practices. This activity can be conducted in a smaller, safer environment by matching a ‘shell group’ with a ‘bubble group’. They will describe their data to each other and then clarify if the data was collected in a sound manner with minimal sources of error. Both groups then combine to produce two recommendations to the class based upon their observations. These will be posted on the wall for the whole class to see (counting down time is useful to urge groups to be efficient).

5. Discrepant Event Number 2 (another POE, 20 minutes or more)
Once the two recommendations are posted, have the students gather around and predict what will happen if you drop a seashell in an acid solution (your solution will be a strong acid – all students should “goggle up” before they approach you). They will be expecting small bubbles. Instruct them to watch as you drop a seashell into a strong acid solution (200 ml beaker with 50 ml of 1M HCl works well). This reaction will be vigorous and produce a significant amount of gas (CO2 but do not tell them). Ask them: what gas is being produced? How can you prove that? Let them figure it out.


Since the shells are composed of CaCO3 this must be CO2. Have students suggest answers. Then demonstrate that the gas will extinguish a flame – proof that is CO2. Next, comes this big question: What is the connection between acidity, shells dissolving and global warming?

One the students have tried this redo this and connect the CO2 probe to the LabQuest2. The graph produced will be an exponential spike in CO2. If you allow this to run over night the CO2 levels return to normal!  

Use this question and all the student recommendations to develop a focus on the problem with ocean acidity. Many school labs do not permit stressful examination of organisms and these experiments take months. However, evidence suggests CO2 is the cause of global warming. Have groups must consider the following (thanks, Bill Nye): What if the pH of the ocean decreases and the CO2 storage ability of the ocean decreases? How will a warmer ocean store CO2? Now you can have a meaningful investigation and discussion – ask the lab groups to reform. The task of the lab groups to use the evidence collected to convince the government we have a significant problem. Write a letter to the Minister of the Environment and express your concerns and use your experimental evidence to support your claims. The letters can be reviewed by the class and if possible, emailed or posted to the Minister of the Environment (federal and provincial).

These experiments generate a lot of discussion and conflict with student conceptions about many things such as – the fragility of the powerful ocean, problems with rising temperatures, and direct connections to their behaviours and our planet’s geochemical cycles.

Teaching Resources 

Below are useful Sites to build your knowledge or for student investigations. There are some great videos and the content is grades 7-12 appropriate.

Digital Resources 

  • DFO - pdf which explains the problem in detail suitable for grades 7-12.
  • DFO -
  • NOAA Ocean Acidification Site -
  • Smithsonian -
  • Review of the Federal Ocean Acidification Research and Monitoring Plan (US).

Useful Scientific References (Canadian and US)

Curran, K. J. (2012). In Azetsu-Scott K., Canada. Department of Fisheries and Oceans and Bedford Institute of Oceanography (Eds.), Ocean acidification: State of the Scotian shelf report. Dartmouth, NS: Dartmouth, NS: Fisheries and Oceans Canada, Bedford Institute of Oceanography.
National Research Council (US) Committee on the Review of the National Ocean Acidification Research and, Monitoring Plan, National Research Council (US) Ocean, Studies Board, & National Research Council (US) Division on Earth and Life Studies, issuing body. (2013). Review of the federal ocean acidification research and monitoring plan. Washington, D.C.: National Academies Press.

Byrne, R. H. (2014). Measuring ocean acidification: new technology for a new era of ocean chemistry. Environ. Sci. Technol.48 (10), 5352–5360. DOI: 10.1021/es405819p
Gattuso, J. P., Mach, K. J., & Morgan, G. (2013). Ocean acidification and its impacts: an expert survey. Climatic Change117(4), 725-738.
Schnoor, J. L. (2013). Ocean acidificationEnviron. Sci. Technol. 47 (21), 11919–11919
DOI: 10.1021/es404263h
Schnoor, J. L. (2014). Ocean Acidification: The Other Problem with CO2. Environ. Sci. Technol. Vol.48(18), pp.10529-30

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