Ocean Acidification: Lab Report
Collaborators:
David Delgado and Jared David
David Delgado and Jared David
Introduction & Problem:
How and why does carbon dioxide affect the pH of water? This is the question that is addressed throughout the lab, and it is a significant topic being that the "surface ocean pH is estimated to have decreased from approximately 8.2 to 8.1 between 1751 and 1994" (Monterey Bay Aquarium). This topic is significant because it could provide us with a deeper understanding of the chemical processes that go on in the ocean. The purpose of this lab is not just to determine if pH increases or decreases as the ocean absorbs more CO2, but also to determine why this change poses a serious environmental threat. Prior knowledge of this exists through the carbonate buffering system, which is losing its ability to maintain equilibrium as seawater becomes more acidic. This threatens to lower the "carbonate ion concentration and saturation states of biologically important calcium carbonate minerals" (PMEL Carbon Program). Overall, protecting the biodiversity of marine ecosystems cannot be addressed without understanding the chemical processes that occur when carbon dioxide is absorbed by water. Reducing carbon dioxide emissions would be a great accomplishment, but addressing this issue must begin with awareness.
Hypothesis:
If the amount of carbon dioxide absorbed by ocean water is increased, then the pH of the water will decrease because it will have a higher concentration of hydrogen-ions as more CO2 dissolves in the solution.
Parts of the Experiment:
Materials and Methods:
a) Materials:
b) Method:
Data & Data Analysis:
a) Data Table:
How and why does carbon dioxide affect the pH of water? This is the question that is addressed throughout the lab, and it is a significant topic being that the "surface ocean pH is estimated to have decreased from approximately 8.2 to 8.1 between 1751 and 1994" (Monterey Bay Aquarium). This topic is significant because it could provide us with a deeper understanding of the chemical processes that go on in the ocean. The purpose of this lab is not just to determine if pH increases or decreases as the ocean absorbs more CO2, but also to determine why this change poses a serious environmental threat. Prior knowledge of this exists through the carbonate buffering system, which is losing its ability to maintain equilibrium as seawater becomes more acidic. This threatens to lower the "carbonate ion concentration and saturation states of biologically important calcium carbonate minerals" (PMEL Carbon Program). Overall, protecting the biodiversity of marine ecosystems cannot be addressed without understanding the chemical processes that occur when carbon dioxide is absorbed by water. Reducing carbon dioxide emissions would be a great accomplishment, but addressing this issue must begin with awareness.
Hypothesis:
If the amount of carbon dioxide absorbed by ocean water is increased, then the pH of the water will decrease because it will have a higher concentration of hydrogen-ions as more CO2 dissolves in the solution.
Parts of the Experiment:
- The control group is constituted by the 10 mL of distilled water.
- The experimental group is made up of the 10 mL of ocean water, which will have CO2 added to it.
- The independent variable is the amount of carbon dioxide added to both solutions.
- The dependent variable is the pH of the solutions after carbon dioxide is added to them, which is measured by the universal indicator.
- The controlled variables include the amount of solution (ocean & distilled water) added to each of the test tubes, the amount of CO2 and universal indicator added to both solutions, the room temperature, and the rest of the materials used in this lab.
Materials and Methods:
a) Materials:
- 2 test tubes
- 20 mL of diluted universal solvent
- 10 mL of salt water
- 10 mL of distilled water
- graduated cylinder
- crushed calcium carbonate (CaCO3)
- straw
- stopwatch
b) Method:
- Use a graduated cylinder to measure 10 mL of ocean water. Pour it into test tube #1. Add 10 mL of the diluted universal indicator (or use 1 mL of the original). Stir and record the pH on the data table.
- Use a graduated cylinder to measure 10 mL of distilled water. Pour it into test tube #2. Add 10 mL of the diluted universal indicator to the test tube as well. Stir and recored the pH on the data table.
- Pull out a stopwatch in order to record the following.
- Place a straw inside of the ocean water sample and blow into it until the color of the solution changes. Record the time that it takes for the solution to change its color from the time that the bubbling begins.
- Repeat step 4 using the sample of distilled water. Record the data in the data table.
- Add crushed calcium carbonate to the ocean water and distilled water test tubes. Record your observations.
Data & Data Analysis:
a) Data Table:
b) Photos:
[#1]
|
[#2]
|
[#3]
|
c) Data Analysis:
The first thing that I noticed while conducting this lab is that both the distilled water and salt water started with a pH of about 7. Upon absorption of our CO2, the pH of both solutions decreased dramatically. This result was anticipated, for our background information told us that the hydrogen-ion concentration would increase as more CO2 dissolved in the solutions. However, it is interesting to note that the pH of the ocean water took slightly longer to finally decrease. I believe that the reason for this observation can be attributed to the carbonate buffer system, which makes this task of absorbing CO2 a natural process for the ocean. Furthermore, this statement can be supported by the observations I made upon adding calcium carbonate to both samples of water.
The distilled water went from a pH of 2 to a pH of 8 after the addition of calcium carbonate, while the ocean water changed significantly more. As can be see by picture #2, the ocean water changed to a blue color with a foamy solute at the bottom. This color indicates a pH of 10, which is more basic than the pH of the distilled water after adding calcium carbonate. I believe that this observation is due to the ocean water's ability to use carbonate in order to maintain equilibrium. In accordance with the background information, it appears that the excess hydrogen ions that we added to the ocean water, which was done by blowing air into the test tube, fixated on the carbonate ions in order to form carbonic acid. This process is part of the carbonate buffering system, which regulates the pH of sea water. If my observations are correct so far, then they would imply that as more carbon is added to the ocean water, there is a lower concentration of calcium carbonate. Although this process may be regulating the pH of ocean water, it is also robbing marine ecosystems of calcium carbonate, which is essential to these communities.
Conclusions:
a) Conclusion Questions:
1. What is the most common pH of surface ocean water?
According to the Monterey Bay Aquarium, the most common pH of surface ocean water is about 8.1.
2. How does your pH of ocean water compare to that reported in the background information? If there is a difference, provide possible explanations.
The background information reports the effects of current in emissions on ocean acidification. The reason that they record a pH of 8.1, while our group observed a final pH of 10 for ocean water is that we did not expose our sample to the excess amount of hydrogen ions which are currently being released into the ocean. Therefore, our results do not depict the the severity of ocean acidification. A pH of 10 is still too basic, for their is not enough CO2 being dissolved in our experiment to show how the ocean'c carbonate buffering system is tipping out of equilibrium.
3. Did the distilled water and ocean water respond differently to the added carbon dioxide? Explain your results.
The distilled water and ocean water both experienced a decrease in pH upon adding carbon dioxide to them. However, the difference lies in the seconds it took for the pH to decrease in both solutions. This change occurred more quickly in the distilled water, while the stimulated ocean water experienced a slower change in pH. A possible explanation to his could be the carbonate buffering system, which regulates the pH of ocean water as a natural process.
4. Explain what happened when calcium carbonate was added to the water samples.
When calcium carbonate was added to the water samples, the pH of both water samples increased. The solutions became less acidic because of the fact that we added a base to them. Calcium carbonate actually neutralized the acidic solutions, which caused the change in color (see data table above).
5. Do you feel the [straw] experiment is a valid model for ocean absorption of carbon dioxide? Explain your answer.
I would not say that the straw experiment is the most valid model for ocean absorption of carbon dioxide. However, we are clearly getting a change in pH, and furthermore the dissolved carbon dioxide decreases the pH of water. This observation seems to substantiate the validity of the experiment, since the background information states that dissolved CO2 increase the hydrogen-ion concentration in ocean water. The only fault (and a major one at that) I see in this model is that it doesn't depict the true amount of CO2 being absorbed by ocean water currently, which downplays the impact of carbon emissions. Nevertheless, it does serve as a valid model and if interpreted correctly, then we can still reach the same general conclusion as other scientists.
b) Conclusion:
The results of the experiment support the hypothesis that if the amount of carbon dioxide absorbed by ocean water is increased, then the pH of the water will decrease because it will have a higher concentration of hydrogen-ions as more CO2 dissolves in the solution. When adding CO2 to both solutions of water, carbonic acid was formed. Then, this carbonic acid differentiated into a hydrogen ion and a bicarbonate ion. These phases are part of a natural process that occurs in the ocean, which I retrieved from the Monterey Bay Aquarium Foundation. In addition, the results of this experiment answered the "why" of this phenomenon, which is very significant to understanding the lab.
Even though the pH of the ocean water was not as low as I had expected, it began to make more sense as I started thinking about the results. The main thing to understand is that this experiment was just a small-scale representation of what goes on in the ocean as more and more CO2 is absorbed. In this experiment, our breath was the only thing providing CO2 to the solution, while in the environment there are billions of people producing CO2, of which almost 50% of is absorbed by oceans (Levitt, Tom). Thus, the fact that our lab was done on a smaller scale emphasizes the current issue with ocean acidification. The excessive amount of hydrogen ions being released into ocean waters (as with the absorption of excess atmospheric CO2) causes the ocean to become more acidic and tips the carbonate buffering system of the ocean (PMEL Carbon Program). This means that ocean water is becoming so acidic that the ocean is using an excessive amount of carbonate ions in order to maintain equilibrium. In turn, this impedes calcification, and many organisms that depend on calcium carbonate for survival are facing a serious threat. Within the lab, the carbonate buffering system was able to neutralize the acidic solution, but this task was easy being that the water absorbed very little CO2. In addition, the data could be misleading due to other factors, such as errors within the experiment.
Understanding the chemical processes behind ocean acidification leads to a very important conclusion. As humans continue to produce more carbon emissions, ocean water will become more acidic, and natural processes will no longer be able to maintain equilibrium. In fact, "estimates of future carbon dioxide levels, based on business as usual emission scenarios, indicate that by the end of this century the surface waters of the ocean could be nearly 150 percent more acidic" (PMEL Carbon Program). Although we have not reached this point yet, the decrease in ocean water's pH is already endangering several marine organisms, which disrupts the food chain in and out of these ecosystems. In addition, "current estimates suggest 30% of coral reefs will be endangered by 2050...because of the effects of ocean acidification and global warming(Levitt, Tom). It is obvious that humans cannot wait until the last minute to act. It is our responsibility to care for the ecosystems which provide us with much of the oxygen that we breathe, and the best way to do so is by reducing CO2 emissions. If this is not done, then not only will marine ecosystems be affected, but humans will also be affected by the loss of biodiversity in the ocean.
Citations:
Levitt, Tom. "Overfished and Under-protected: Oceans on the Brink of Catastrophic Collapse." CNN. Cable News Network, 01 Jan. 1970. Web. 04 Sept. 2014. <http://www.cnn.com/2013/03/22/world/oceans-overfishing-climate-change/>.
The Power of PH: Changing Ocean Chemistry. N.p.: Monterey Bay Aquarium Foundation, 2010. PDF.
"What Is Ocean Acidification?." PMEL Carbon Program. National Oceanic and Atmospheric Administration, n.d. Web. 2 Sept. 2014.
The first thing that I noticed while conducting this lab is that both the distilled water and salt water started with a pH of about 7. Upon absorption of our CO2, the pH of both solutions decreased dramatically. This result was anticipated, for our background information told us that the hydrogen-ion concentration would increase as more CO2 dissolved in the solutions. However, it is interesting to note that the pH of the ocean water took slightly longer to finally decrease. I believe that the reason for this observation can be attributed to the carbonate buffer system, which makes this task of absorbing CO2 a natural process for the ocean. Furthermore, this statement can be supported by the observations I made upon adding calcium carbonate to both samples of water.
The distilled water went from a pH of 2 to a pH of 8 after the addition of calcium carbonate, while the ocean water changed significantly more. As can be see by picture #2, the ocean water changed to a blue color with a foamy solute at the bottom. This color indicates a pH of 10, which is more basic than the pH of the distilled water after adding calcium carbonate. I believe that this observation is due to the ocean water's ability to use carbonate in order to maintain equilibrium. In accordance with the background information, it appears that the excess hydrogen ions that we added to the ocean water, which was done by blowing air into the test tube, fixated on the carbonate ions in order to form carbonic acid. This process is part of the carbonate buffering system, which regulates the pH of sea water. If my observations are correct so far, then they would imply that as more carbon is added to the ocean water, there is a lower concentration of calcium carbonate. Although this process may be regulating the pH of ocean water, it is also robbing marine ecosystems of calcium carbonate, which is essential to these communities.
Conclusions:
a) Conclusion Questions:
1. What is the most common pH of surface ocean water?
According to the Monterey Bay Aquarium, the most common pH of surface ocean water is about 8.1.
2. How does your pH of ocean water compare to that reported in the background information? If there is a difference, provide possible explanations.
The background information reports the effects of current in emissions on ocean acidification. The reason that they record a pH of 8.1, while our group observed a final pH of 10 for ocean water is that we did not expose our sample to the excess amount of hydrogen ions which are currently being released into the ocean. Therefore, our results do not depict the the severity of ocean acidification. A pH of 10 is still too basic, for their is not enough CO2 being dissolved in our experiment to show how the ocean'c carbonate buffering system is tipping out of equilibrium.
3. Did the distilled water and ocean water respond differently to the added carbon dioxide? Explain your results.
The distilled water and ocean water both experienced a decrease in pH upon adding carbon dioxide to them. However, the difference lies in the seconds it took for the pH to decrease in both solutions. This change occurred more quickly in the distilled water, while the stimulated ocean water experienced a slower change in pH. A possible explanation to his could be the carbonate buffering system, which regulates the pH of ocean water as a natural process.
4. Explain what happened when calcium carbonate was added to the water samples.
When calcium carbonate was added to the water samples, the pH of both water samples increased. The solutions became less acidic because of the fact that we added a base to them. Calcium carbonate actually neutralized the acidic solutions, which caused the change in color (see data table above).
5. Do you feel the [straw] experiment is a valid model for ocean absorption of carbon dioxide? Explain your answer.
I would not say that the straw experiment is the most valid model for ocean absorption of carbon dioxide. However, we are clearly getting a change in pH, and furthermore the dissolved carbon dioxide decreases the pH of water. This observation seems to substantiate the validity of the experiment, since the background information states that dissolved CO2 increase the hydrogen-ion concentration in ocean water. The only fault (and a major one at that) I see in this model is that it doesn't depict the true amount of CO2 being absorbed by ocean water currently, which downplays the impact of carbon emissions. Nevertheless, it does serve as a valid model and if interpreted correctly, then we can still reach the same general conclusion as other scientists.
b) Conclusion:
The results of the experiment support the hypothesis that if the amount of carbon dioxide absorbed by ocean water is increased, then the pH of the water will decrease because it will have a higher concentration of hydrogen-ions as more CO2 dissolves in the solution. When adding CO2 to both solutions of water, carbonic acid was formed. Then, this carbonic acid differentiated into a hydrogen ion and a bicarbonate ion. These phases are part of a natural process that occurs in the ocean, which I retrieved from the Monterey Bay Aquarium Foundation. In addition, the results of this experiment answered the "why" of this phenomenon, which is very significant to understanding the lab.
Even though the pH of the ocean water was not as low as I had expected, it began to make more sense as I started thinking about the results. The main thing to understand is that this experiment was just a small-scale representation of what goes on in the ocean as more and more CO2 is absorbed. In this experiment, our breath was the only thing providing CO2 to the solution, while in the environment there are billions of people producing CO2, of which almost 50% of is absorbed by oceans (Levitt, Tom). Thus, the fact that our lab was done on a smaller scale emphasizes the current issue with ocean acidification. The excessive amount of hydrogen ions being released into ocean waters (as with the absorption of excess atmospheric CO2) causes the ocean to become more acidic and tips the carbonate buffering system of the ocean (PMEL Carbon Program). This means that ocean water is becoming so acidic that the ocean is using an excessive amount of carbonate ions in order to maintain equilibrium. In turn, this impedes calcification, and many organisms that depend on calcium carbonate for survival are facing a serious threat. Within the lab, the carbonate buffering system was able to neutralize the acidic solution, but this task was easy being that the water absorbed very little CO2. In addition, the data could be misleading due to other factors, such as errors within the experiment.
Understanding the chemical processes behind ocean acidification leads to a very important conclusion. As humans continue to produce more carbon emissions, ocean water will become more acidic, and natural processes will no longer be able to maintain equilibrium. In fact, "estimates of future carbon dioxide levels, based on business as usual emission scenarios, indicate that by the end of this century the surface waters of the ocean could be nearly 150 percent more acidic" (PMEL Carbon Program). Although we have not reached this point yet, the decrease in ocean water's pH is already endangering several marine organisms, which disrupts the food chain in and out of these ecosystems. In addition, "current estimates suggest 30% of coral reefs will be endangered by 2050...because of the effects of ocean acidification and global warming(Levitt, Tom). It is obvious that humans cannot wait until the last minute to act. It is our responsibility to care for the ecosystems which provide us with much of the oxygen that we breathe, and the best way to do so is by reducing CO2 emissions. If this is not done, then not only will marine ecosystems be affected, but humans will also be affected by the loss of biodiversity in the ocean.
Citations:
Levitt, Tom. "Overfished and Under-protected: Oceans on the Brink of Catastrophic Collapse." CNN. Cable News Network, 01 Jan. 1970. Web. 04 Sept. 2014. <http://www.cnn.com/2013/03/22/world/oceans-overfishing-climate-change/>.
The Power of PH: Changing Ocean Chemistry. N.p.: Monterey Bay Aquarium Foundation, 2010. PDF.
"What Is Ocean Acidification?." PMEL Carbon Program. National Oceanic and Atmospheric Administration, n.d. Web. 2 Sept. 2014.