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Ocean Acidification

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Earth and Environmental Sciences
Main Image
Earth and Environmental Sciences
Created by
Ryerson University
Activity Language
Time Needed for Activity

Students will learn how the production of carbon dioxide contributes to environment issues such as ocean acidification.

Students will investigate acids and bases in water systems and their effects on the environment. This lesson will introduce acids and bases in familiar products and use cabbage indicator to identify them. Students will learn how the production of carbon dioxide contributes to environmental issues such as ocean acidification and will be tasked to produce carbonic acid. 

What You Need

Cabbage Juice Indicator + Egg Shell Demonstration

  • Cups (51 total, 6 per group plus 2 for egg demo, plus one extra)
  • Masking tape to label cups
  • Vinegar (approx. 320 mL)
  • Baking soda (approx. 125 g or 1/4 of box)
  • Salt (approx. 125g)
  • Lemon juice (approx. 24 mL)
  • Red cabbage juice (approx. 300 mL)
  • Markers (9)
  • Boiled eggs, or just the egg shell from one egg (collected earlier)
  • Droppers (9)
  • Straws (9)
  • Spoon
  • Paper towel

To prepare the cabbage juice

  • Red cabbage (one)
  • Blender or food processer
  • Water
  • Mason jar or air tight container

Activity Guide:

Safety Notes

Ensure you are familiar with Let's Talk Science's precautions with respect to safe virtual delivery to youth.

Remind students not to consume/drink any of the liquids in this workshop.

Red cabbage juice may stain if spilled on carpet or clothes. 

As an allergy precaution, ensure that the educator is aware that the workshop includes the use of lemon juice, vinegar, red cabbage and eggs. No direct contract with these substances is required however inadvertent contact may occur.

What To Do

Pre-Activity Prep

  • Prepare red cabbage juice prior to the activity date.
    • Remove the outer leaves of the red cabbage and discard. 
    • Tear up the red cabbage leaves into smaller chunks and place in the blender or food processer. Use mostly the leafy part of the red cabbage and less of the stems for better results.
    • Fill the blender or food processor approximately 3/4 full with leaf chunks.
    • Add water so that all the leaf chunks are submerged (do not add more than that).
    • Let soak for 15 minutes.
    • Blend until all large chunks have been blended. Let soak again for 15 minutes.
    • Strain the liquid and store in an airtight container to use in the experiment. Discard the blended bits of cabbage. The straining does not have to be perfect.
    • You should have approx. 300mL of cabbage juice now. Refrigerate until the day of the activity.
  • Collect egg shells from one egg prior to the activity date.

Egg Shell Demonstration

  • Fill one clear plastic cup half-full with water, and the other half-full with vinegar. 
  • Divide the egg shells between the two cups and submerge the shells. 
  • Have students make observations about what they see. Record these observations on the classroom board (optional).
  • Set the cups aside. 
  • Come back to the egg shells at the end of the session. There should be some bubbles forming on the shell in the vinegar and some of the shell may be dissolved.
  • Ask students to share their observations with the class.
  • Discuss the impact of acid in our oceans on animals that have shells (crustaceans and some mollusks).
  • The egg shells can be left in the cup with the teacher for the students to make more observations at the end of the day and/or the next day (the egg shell in vinegar should totally dissolve in a few hours).

Cabbage Indicator Experiment

  • Separate students into groups of 3 (the materials are enough for 8 groups). Each group should have 6 cups, 1 dropper and 1 straw.
  • Introduce the concept of acids and bases.
  • Label the cups 1-6 and have students fill them 1/3 of the way with:
    • Water
    • Half vinegar and half water
    • Water and 1/2 tsp of baking soda
    • Water and 1/2 tsp salt
    • Water and 3 mL of lemon juice (3 full droppers)
    • Cabbage juice 
  • Have students gently swirl their cups until all the salt and baking soda are dissolved.
  • Instruct students to add 2-3 droppers full of cabbage juice from cup #6 to each of the other cups (#1-5). Discuss the colour changes they see (note these on the classroom board) and label each cup an acid, base or neutral.
    • Purple/blue represents a neutral solution.
    • Pink represents an acidic solution.
    • Blue represents a basic solution. 
  • Introduce the concept of ocean acidification and Henry's Law. Use the classroom board to illustrate the concepts (optional).

Challenge

  • Ask students to add more cabbage juice indicator into cup #1 (water + cabbage juice indicator).
  • Each group will assign someone to make bubbles using the straw provided for 2 minutes. The rest of the group members will be in charge of observing what happens in the cup as their partner blows bubbles.
  • Compare the colour changes at the end of the 2 minutes. Why did the colour change?

Titration Challenge (optional)

  • Ask the students to take their cup of vinegar solution and try to make it neutral. 
  • Encourage students to use their eye dropper to mix solutions so they do not accidentally add too much. 
  • If they finish that quickly, they can start with their basic solution and add the lemon juice solution to make it neutral too.

Wrap-up

  • Ask students to clean up their experiment: the dropper will need to be filled with clean water 2-3 times to rinse it out. All of the cups from the experiment should be rinsed and dried.
  • Discuss possible careers related to the topics mentioned and what they will need to do (schooling, experience, etc.) in order to get into those careers.

Discovery

What's Happening?

pH is a measurement of a number of small molecules, called hydrogen ions (H+), in a liquid. If you have a lot of H+, you will be at the low end of the pH scale and be very acidic. If you have fewer H+, you will be on the high end of the pH scale and will be very basic. An acid/base indicator is a chemical that changes colour when an acid or base is present in a liquid. Red cabbage juice is a natural pH indicator, it will turn pink in the presence of an acid and blue in the presence of a base.

Oceans absorb roughly half of the carbon dioxide in the air because of Henry's law. Henry's Law states that at a constant temperature, the amount of given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in a liquid. This means that the amount of a certain gas in the air is roughly equal to the amount of that gas dissolved in a liquid. As more carbon dioxide is released into the atmosphere, more is dissolved in the oceans, increasing the concentration of H+ ions (making the ocean more acidic). Ultimately this results in a reduction of carbonate ions, which is required for the formation of many animal shells in the ocean.

What's Happening?

pH is a measurement of a number of small molecules, called hydrogen ions (H+), in a liquid. If you have a lot of H+, you will be at the low end of the pH scale and be very acidic. If you have fewer H+, you will be on the high end of the pH scale and will be very basic. An acid/base indicator is a chemical that changes colour when an acid or base is present in a liquid. Red cabbage juice is a natural pH indicator, it will turn pink in the presence of an acid and blue in the presence of a base.

Oceans absorb roughly half of the carbon dioxide in the air because of Henry's law. Henry's Law states that at a constant temperature, the amount of given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in a liquid. This means that the amount of a certain gas in the air is roughly equal to the amount of that gas dissolved in a liquid. As more carbon dioxide is released into the atmosphere, more is dissolved in the oceans, increasing the concentration of H+ ions (making the ocean more acidic). Ultimately this results in a reduction of carbonate ions, which is required for the formation of many animal shells in the ocean.

Why Does It Matter?

Calcium carbonate is the building block for animal shells in the ocean. When carbonate is not available to react with calcium, there is less available for crustaceans and mollusks to build their shells with. As a result, their shells become softer and weaker- less able to protect them.

Corals also use calcium carbonate to build their skeletons, so the increased acidification in the ocean limits the availability of these building blocks. Corals form the basis for the complex ecological system, so many organisms that rely on corals will also be affected by the decay and reduction in coral.

Why Does It Matter?

Calcium carbonate is the building block for animal shells in the ocean. When carbonate is not available to react with calcium, there is less available for crustaceans and mollusks to build their shells with. As a result, their shells become softer and weaker- less able to protect them.

Corals also use calcium carbonate to build their skeletons, so the increased acidification in the ocean limits the availability of these building blocks. Corals form the basis for the complex ecological system, so many organisms that rely on corals will also be affected by the decay and reduction in coral.

Investigate Further

  • For younger grades or to save time, you may want to prepare the liquids for each group before the activity starts. 

Investigate Further

  • For younger grades or to save time, you may want to prepare the liquids for each group before the activity starts. 

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