Download Sydney Dunigan Ocean Acidification Lab AP Environmental Science

Sydney Dunigan
Ocean Acidification Lab
AP Environmental Science Heritage High School
Collaborator:
Taylor Cielo
Introduction:
Within the past 300 years, the acidity of the ocean’s pH is estimated to have increased from 8.2 to 8.1,
or a 26% increase in acidity. 26% increase is enough to hinder the balance of the ocean; the ocean must
remain at a specific level of chemicals and pH level in order to support the marine life. If this rise persists, it
could end an overwhelming loss of biodiversity in ocean’s ecosystems. Through this experiment, the matter of
carbon dioxide raising or decreasing the acidity of the ocean will be addressed. According to NASA, “The ocean
would continue to soak up more and more carbon dioxide until global warming heated the ocean enough to
slow down ocean circulation. Water trapped at the surface would become saturated, at which point, the
ocean would slow its carbon uptake”. Buffering is the hope for the ocean, a hope that it can resist the change
in acidity and stop soaking up the harmful CO2.
Problem: How does carbon dioxide affect the pH of water?
Hypothesis: If carbon dioxide is added to the water, the pH of the water will then lower, thus, an acidic ocean.
Parts of the Experiment:
Control Group: The 10 mL of distilled water is the control group.
Experimental Group: The 10 mL of ocean water is the experimental group.
Independent Variable: The type of water (ocean or distilled) used is the independent variable.
Dependent Variable: The color of the universal indicator is the dependent variable, or the pH.
Controlled Variables: The materials, the room temperature, the amount of water poured into each
graduated cylinder, and the amount of carbon dioxide and universal indicator added to the water are
the controlled variables.
Materials:
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Two test tubes
Graduated cylinder
Two plastic pipets
Universal indicator
Salt water
Distilled water
One straw
Methods:
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Put 1ml of universal indicator into 10 ml of ocean water, record the pH
Put 1 ml of universal indicator into 10 ml of distilled water, record the pH
Sydney Dunigan
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Using a straw, slowly breathe into the test tubes, record the time it takes for the color to change
Add 1g of crushed CaCO3 to each test tube, record the results
Data: Below are the stages of the ocean water test tubes:
pH Start
Time for pH
change
pH End
pH with CaCO3
Ocean
Water
5
to 15 seconds
6
8
Distilled
Water
6
7 seconds
4
7
Data Analysis:
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Ocean water changed color slower than the distilled water, this was because of a buffering system
within the ocean water
When calcium carbonate, a base, was added to the ocean water, the solution turned from a dark
orange to yellow-green, to blue.
When calcium carbonate was added to the distilled water, the solution turned from yellow to green.
Conclusion:
The pH of the ocean is on average, recently, about 8.1. The acidity of the “ocean water” that we used was
about a 5, but a lot of different elements could have accounted for this. For instance, we had clean water that
was added to with salt. In an actual ocean, there are many bacteria and germs in the water, which could very
well raise the pH to be basic. Or, materials could have been contaminated previous to the lab. The ocean
water showed a greater pH change by the end of the experiment. It rose from a 5 to a 6 when carbon dioxide
was added to it, and then spiked to an 8, which is not the expected outcome I predicted. Ideally, the starting
pH of the “ocean water” would be close to that of the actual ocean. However, the distilled water changed in a
different way, first decreasing and then spiking. Whether or not this experiment is a valid way to measure the
effects of carbon in the water, the ending pH were relatively similar. This could lead one to believe that yes,
carbon affects ocean water, but not because it contains salt. It affects distilled water as well, giving both of
them similar levels of pH. When calcium carbonate was added to the water, both samples became more basic.
One faster than the other, but they still ended up around the same level. The ocean water rose from a 6 to an
8, and the distilled from a 4 to a 7. Both of these pH levels were close to that of our oceans, an outcome one
could easily predict, thus the point of the experiment.
Citations:
The Power of PH: Changing Ocean Chemistry. N.p.: Monterey Bay Aquarium Foundation, 2010. PDF. 2015 Jan.
28
Riebeek, Holli. "The Ocean's Carbon Balance : Feature Articles." The Ocean's Carbon Balance : Feature Articles.
Earth Observatory, NASA, 30 June 2008. Web. 28 Jan. 2015.