Ocean Acidification Lab
Collaborators: Sarah Pippin and Amanda Goodale
Introduction and Problem
The goal of this Ocean Acidification lab is to understand how carbon dioxide
affects the pH of water. This topic is highly invaluable in understanding the causes of
ocean acidification and ways in which humans can work to reduce it. Ocean acidification
has become a growing problem in the world’s bodies of saltwater as it presents a
significant danger to most of marine life. Ocean acidification occurs when carbon
dioxide is absorbed by seawater, which creates chemical reactions that reduce the pH of
the water and carbonate ion concentration (PMEL Carbon Program). Excessive amounts
of carbon dioxide to the ocean waters from human processes like the burning of fossil
fuels have the potential to be harmful to many ocean organisms, especially calcifying
species. Calcium carbonate minerals are essential to the process of building shells and
skeletons for marine organisms. When carbon dioxide reacts with water, it produces
hydrogen ions, which lower the ocean’s pH and compete with the shells for carbonate.
Therefore, the more carbon dioxide absorbed by the ocean water and the lower the pH,
the less carbonate available for marine organisms’ shells and skeletons. The ocean is
considered one of the world’s largest carbon sinks, as it absorbs about a quarter of the
carbon dioxide released into the atmosphere, and while it keeps a lot of carbon dioxide
out of the air, it also is detrimental to a lot of the sea life (Ocean Acidification: The Other
Carbon Dioxide Problem).
Hypothesis
This experiment is testing the compared changes in the pH of distilled and ocean
water when both carbon dioxide and calcium carbonate are added. When we add carbon
dioxide and calcium carbonate to both ocean and distilled water, I predict that the pH of
the distilled water will change more than the pH of ocean water because of the ocean
water’s carbonate buffer system.
Parts of the Experiment
Control group- distilled water
Experimental group- ocean water
Independent variable- type of water , either ocean or distilled
Dependent variable- pH of water
Controlled variables- test tubes, universal indicator, carbon dioxide, calcium
carbonate
Materials and Methods
The materials utilized in this experiment include two test tubes, universal
indicator, ocean water, distilled water, and straw. The first step in the Ocean
Acidification Lab was to measure 10mL of ocean water with a graduated cylinder and
pour it into a test tube labeled #1. Next, 10mL of universal indicator was added, the
product was stirred, and the pH was recorded. A similar procedure was followed for
distilled water: 10mL was measured using a graduated cylinder, it was poured into
another test tube labeled #2, 10mL of universal indicator was added, the product was
stirred, and the pH was recorded. A straw was then partially inserted into the solution of
ocean water and used for the experimenter to blow carbon dioxide into test tube #1 until
bubbles were seen. As soon as the solution began bubbling a stopwatch was used to
mark the start time. When the color changed the stopwatch was immediately stopped to
mark the end time. The results were recorded. This was repeated for test tube #2 and the
results recorded. Finally, crushed calcium carbonate was added to each of the two test
tubes, and the observations were recorded.
Data and Data Analysis
Solution
Ocean Water
Distilled
Water
Measured
pH
7
Measured
pH after
adding
CO2
3
Time (in seconds) for pH to
change
10 seconds
7
6
12 seconds
Observations with calcium
carbonate
more basic than distilled water
changed from acidic to basic
1. According to this lab, the most common pH of surface ocean water is 7, because when
we applied the universal indicator to the saltwater, the color changed to green,
representing the neutral pH.
2. We found in this experiment that the pH of ocean water is 7, while in the background
information it approximates the ocean’s pH to 8.1. In any experiment, one tries to mimic
what happens in the natural world, but it is not always completely accurate. It also might
depend on whether the salt water we used in this experiment was actually ocean water, or
whether it was just water with salt added to it.
3. The distilled water and ocean water responded differently to the added CO2. While
both solutions became more acidic after the addition of CO2, the ocean water’s pH
became much lower than that of the distilled water, showing that it was more acidic. The
universal indicator showed the color of ocean water change from the neutral green pH
color to red, indicating a pH of about 3 or 4. The distilled water transformed from green
to a yellowish color, indicating a pH of approximately 6 after the CO2 addition to the
solution.
4. When calcium carbonate was added to the water samples, both turned a light blue
color, indicating they became more basic at around a pH of 9. The ocean water, though,
was a slightly darker shade of blue than the distilled water, showing it was a little more
basic.
(The left test tube is distilled water, and the right is ocean water.)
5. I feel the ocean acidification lab was a valid model for ocean absorption of CO2. The
lab shows the changes in pH through a visual demonstration using universal indicator and
color. It thoroughly exhibits the change in ocean water when CO2 is added by showing
the color change of pH from around neutral to significantly acidic, from the color green
to red.
Conclusion
At the beginning of this lab, I hypothesized that the pH of distilled water would
change more when carbon dioxide and calcium carbonate were added because of the
ocean water’s carbonate buffer system. But once we performed the lab, I discovered that
this hypothesis was not valid, because the ocean water’s pH actually changed more than
the distilled in response to the CO2 and calcium carbonate. This is because an increased
amount of carbon dioxide into the oceans has caused an excessive amount of hydrogen
ions released into the salt water. This causes the ocean to become more acidic and
creates imbalance in the carbonate buffering system. The article “What is Ocean
Acidification?” by NIWA explains, “The carbonate buffer system… is a series of
reactions, in which dissolved CO2 is converted to bicarbonate using carbonate as a
buffer, that has kept the level of H+ protons (and therefore pH) constant. The amount of
CO2 entering the surface ocean has increased over the last century and exceeded the
natural replenishment rate of carbonate, with the result that the H+ has increased, making
the water more acidic.”
Understanding how carbon dioxide affects ocean water is one of the first steps in
learning how to fix it. Excess amount of carbon dioxide originally produced from many
of earth’s man-made systems, like burning fossil fuels, tips the ocean’s buffering system
and causes the saltwater to increase in acidity. This process is commonly referred to as
ocean acidification and is detrimental to many of the ocean’s creatures, especially
calcified organisms. “What is Ocean Acidification?” by Oceana claims, “If we continue
on our current emissions trajectory, by 2050 ocean pH will be lower than at any point in
the last 20 million years.” Actions must be taken now to attempt to resolve or reduce the
issue of human processes that put the natural world at risk.
Works Cited
"Ocean Acidification: the Other Carbon Dioxide Problem." PMEL Carbon Program.
N.p., n.d. Web. <http://www.pmel.noaa.gov/co2/story/Ocean+Acidification>.
"PH and Color Change." Middle School Chemistry. American Chemical Society, n.d.
Web. <http://www.middleschoolchemistry.com/lessonplans/chapter6/lesson8>.
"What Is Ocean Acidification?" NIWA Taihoro Nukurangi. NIWA, n.d. Web.
<http://www.niwa.co.nz/coasts-and-oceans/faq/what-is-ocean-acidification>.
"What Is Ocean Acidification?" Oceana: Protecting The World's Oceans. Oceana, n.d.
Web. <http://oceana.org/en/our-work/climate-energy/ocean-acidification/learn-act/whatis-ocean-acidification>.
"What Is Ocean Acidification?" PMEL Carbon Program. N.p., n.d. Web.
<http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F>.