Section 3 - Introduction to Ocean Acidification: How does CO2 cause change in the pH of water?
Overview and Purpose
This lesson reinforces the fundamental concept of ocean acidification: water becomes more acidic as carbon dioxide (CO2) is absorbed from the atmosphere. Students will design and conduct an experiment to test this concept, using indicator solutions to measure changes in acidity. This activity builds upon previous lessons covering carbon, the greenhouse effect, and the basics of ocean acidification, providing students with hands-on experience in scientific inquiry.
NGSS STANDARDS
5-ESS3-1
Obtain and combine information about ways individual communities use science ideas to protect the Earth’s resources and environment.
HS-PS1-2
Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.
MS-LS2-1
Analyze and interpret data to provide evidence for the effects of resource availability on organisms and populations of ecosystems.
Science and Engineering Practices:
- Developing and Using Models
- Planning and Carrying Out Investigations
OBJECTIVES
- Students will design and conduct an experiment to demonstrate how CO2 causes water to become more acidic.
- Students will practice using indicator solutions (bromothymol blue, pH strips, pH meter, or cabbage indicator) to measure changes in pH.
- Students will develop and use models to represent the process of ocean acidification.
- Students will analyze and interpret data to draw conclusions about the relationship between CO2 and water acidity.
MATERIALS NEEDED
- Student worksheets (including experimental design prompts and analysis questions)
- Presentation slides: What is Ocean Acidification, Ocean Acidification investigation (PowerPoint or equivalent)
- Teacher demonstration materials: 1 cup, straw, water, bromothymol blue
- Student group materials:
- Paper or reusable straws (1-2 per group)
- Clear cups (2 per group)
- Water (enough to fill each cup halfway)
- Bromothymol blue solution (Buy on Amazon, or here)
- pH indicator (pH meter, pH test strips, or homemade with cabbage (see instructions here)
PROCEDURE
Part 1:
- Using slide presentation 3a: What is Ocean Acidification?, introduce students to the relationship between atmospheric CO2 and ocean acidification.
Part 2:
- Before class: Acquire supplies, arrange for enough supplies for each group. Also, modify slide 11 to reflect the instructions that apply to your pH indicator.
- Use slide presentation 3b: Ocean Acidification investigation slides.
- (5 min) Display the aim and do now as students arrive. Encourage students to come up with answers with classmates.
- (5 min) Elicit answers and assess whether brief review is needed (available on next two slides).
- (15 min) Establish today’s goal, to conduct an experiment. Have students brainstorm materials and procedures. If you’ve already set out materials, have students think about how each will be used.
- (5 min) Distribute materials and worksheets.
- (10 min) Students read questions 1-4 to themselves, then the teacher runs the videos and performs the demonstration as they answer.
- (15 min) Students plan their experiment by responding to 6 a-e on the worksheet. Allow productive struggle as students attempt to answer with their groups. Circulate and facilitate discussion.
- Differentiation: Use slide 9 to work through questions as a class.
- Extension: Have students sketch the two experimental setups.
- (10 min) Have students conduct experiment. Encouraging productive struggle will allow students to figure out the steps themselves.
- Differentiation: Use slide 10 to work through steps as a class.
- (15 min) Clean up and Analysis questions: Have students clean up their area, then return to their seats. Now they will work independently to answer the three conclusion questions, in order to make sure each student individually achieved the goals of this lesson.
- Differentiation: Use slide 13 to complete the conclusion questions together as a class
- Extension: Students may select 1 or more of Extension and Analysis questions to explore the topic in depth.
DIFFERENTIATION
Support
- Provide guided worksheets with simplified instructions.
- Use visual aids and diagrams to explain concepts.
- Conduct parts of the experiment as a whole class.
- Use slides to go over the experiment, and conclusion questions.
Extension
- Have students design variations of the experiment to test different variables.
- Ask students to research and present on the effects of ocean acidification on specific marine organisms.
- Have students sketch the experimental set up.
ASSESSMENT
Successful students will be able to explain what each component of the activity is demonstrating with respect to ocean acidification. Observe student participation in group discussions and experimental design. Evaluate student experimental setups and data collection. Assess student responses to the analysis questions on the worksheet. Review student concept maps for accuracy and completeness.
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