Modeling the Acidification of the Ocean

By Kate Fraser on Apr 05, 2015

Recent science articles have discussed how the increase in Carbon Dioxide in our atmosphere is contributing to increased levels of carbon dioxide in the ocean.

As CO2 is added to the water, carbonic acid is created. Since CO2 is an odorless, colorless, tasteless gas, it is difficult for students to understand that additional CO2 really does change the chemistry of the water. The experiment we outline here gives all students including those with a visual impairment some concrete evidence that change has occurred! 


  • This activity uses cabbage juice as a pH indicator. This can be prepared in advance.
  • Red Cabbage Solution Indicator (can be purchased in powdered from Science Supply companies)  
  • This link has a recipe for preparing it:
  • Prior to the activity measure out the same amount of sea water into each of the beakers needed for the number of students.


  • Red Cabbage Solution Indicator 
  • Ocean water (about 6 ounces for each student)
  • Beakers (for the ocean water and distilled water)
  • Pipettes
  • Straws
  • Distilled water
  • pH scales in color, in print and in Braille
  • Color test II (available from APH) reads colors on surfaces and states the color out loud
  • Talking Vernier Lab Quest
  • pH sensor
  • Safety goggles
  • Lab aprons
  • Paper towels


  1. Measure the pH of the ocean water using the talking Lab Quest and pH sensor and record information. (Ocean water is usually slightly basic, around 8  on the pH scale)
  2. Rinse the sensor in distilled water and leave in beaker.
  3. Note the color of the cabbage juice solution, using the color tester.
  4. Add several drops of red cabbage solution to the ocean water using the pipette
  5. Note the color change of the ocean water with the color tester, and compare it to the colors on the chart. It may be blue, which indicates a slightly basic solution.
  6. Using the straw, blow into the ocean water for about 30 seconds. Since you exhale carbon dioxide, you are adding CO2 to the water.
  7. Using the pH sensor and the talking lab quest, record the pH.  The number may have decreased indicating an increase in acidity.  Reminder: each number on the pH scale represents a 10 fold change in the acidity or basicity. Even a small change downward is significant. Record your data.
  8. Use the talking color reader to record the color and compare to the color chart.  The color may have become more purple or red, which indicates neutral or slightly acid.
  9. Calculate the amount of the change in pH.  Discuss your findings with your classmates.


If you are interested in using your cabbage juice in other experiments to determine pH of solutions, store it covered in the refrigerator for no longer than one week. 

NGSS Standards:

Human impacts on Earth systems: Human activities have altered the biosphere, sometimes damaging it, although changes to environments can have different impacts for different living things. Activities and technologies can be engineered to reduce people’s impacts on Earth.
Collage of Modeling Acidification with students with visual impairments



Read more about: Earth & Space Science, Science, STEM