Lab 2 Ocean Acidification

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Dec 6, 2023

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Success Criteria: Explain what ocean acidification is and why it is happening. Describe ways in which individual species and marine ecosystems might respond to ocean acidification. Describe how ocean acidification may impact the ability of oceans to store carbon in deep sea sediments. Learn about pH chemistry in sea water Conduct a short experiment to investigate the relationship between increased CO2, acidity and pH Analyze and compare times series data sets of atmospheric CO2, sea surface CO2 and ocean pH Introduction: Historically, changes in climate have been influenced by a combination of human and natural factors, but these days climate c hange is mostly due to human activity, like fossil fuel use and modern agricultural practices. (The words "climate" and "weather" are sometim es used interchangeably, but there is a clear distinction between them: weather indicates the current state of atmospheric conditions , whereas climate reflects weather over many years.) Greenhouse gases are needed for Earth to retain heat from the Sun. But human activity has created an excess of these gases, so that now too much of the Sun's heat gets trapped in our atmosphere. The increase in greenhouse gas emission also affects our ocean. The ocean is a natural carbon sink that accumulates and store s carbon- containing chemical compounds. By absorbing much of the excess carbon and heat from the atmosphere, the ocean helps regulate the Earth’s temperature. In fact, the ocean absorbs approximately 25-30% of human produced carbon dioxide. Chemical compounds, such as carbon dioxide from the atmosphere, dissolve into the ocean's surface through diffusion and then move into the deep ocean. CO 2 reacts with water in our oceans to form a weak acid called carbonic acid: CO 2 (aq) + H 2 O (l) --> H 2 CO 3 (aq) This process is responsible for the acidification of our oceans. Ocean acidity, as measured by pH, has increased by 30% since the industrial revolution and scientists predict pH will continu e to change as increasing amounts of carbon dioxide are absorbed by oceans. Because the chemistry of the oceans is important to life, subtle changes in that chemistry may have significant effects on the health of individual species and on entire ecosystems. Corals and other shell -builders such as oysters, lobsters and pteropods may be at risk as ocean pH chemistry becomes more acidic. In this experiment, you will carry out a class experiment to test the effects of increased amounts of CO 2 on pH. This will be done by analyzing the process of two distinct chemical reactions. Experiment 1 will simulate the reactions that have been occurring in factories throughout the industrial revolution. You will simulate the effect of industry produced carbon dioxide by combining acetic acid and sodium bicarbonate. Pre-Lab Activity: Create your Red Cabbage pH Indicator Red Cabbage Basics: Red cabbage contains a pigment molecule called flavin (an anthocyanin). This water-soluble pigment is also found in apple skins, plums, poppies, cornflowers, and grapes. Very acidic solutions will turn anthocyanin into a red color. Neutral solutions result in a purplish color. Basic solutions appear in greenish-yellow. Therefore, you can determine the pH of a solution based on the color that it turns the anthocyanin pigments in red cabbage juice. The color of the juice changes in response to changes in its hydrogen ion concentration; pH is the -log[H+]. Acids will donate hydrogen ions in an aqueous solution and have a low pH (pH 7). Red cabbage • Blender or knife • Boiling water • Filter paper (coffee filters work well) • One large glass beaker or another glass container • Materials You Will Need: Lab 2: Ocean Acidification Friday, September 18, 2020 9:03 PM Unit 1 Climate Change Page 1

Chop the cabbage into small pieces until you have about 2 cups of chopped cabbage. Place the cabbage in a large beaker or oth er glass container and add boiling water to cover the cabbage. Allow at least 10 minutes for the color to leach out of the cabba ge. Alternatively, you can place about 2 cups of cabbage in a blender, cover it with boiling water, and blend it. 1. Filter out the plant material to obtain a red-purple-bluish colored liquid. This liquid is at about pH 7. The exact color you get depends on the pH of the water. 2. Pour about 50 – 100 mL of your red cabbage indicator into each 250 mL beaker. 3. Add various household solutions to your indicator until it changes color. Use separate containers for each household solution — you don't want to mix chemicals that don't go well together. 4. Procedure Red Cabbage pH Indicator Colors pH 2 4 6 8 10 12 Color Red Purple Violet Blue Blue-Green Greenish Yellow Tips and Safety: This demo uses acids and bases, so use safety goggles and gloves, particularly when handling strong acids (HCl) and strong bases (NaOH or KOH). Chemicals used in this demo may be safely washed down the drain with water. You can conduct a neutralization experiment using a cabbage juice indicator. First, add an acidic solution such as vinegar or lemon, then juice until a reddish color is obtained. Add baking soda or antacids to return the pH to a neutral 7. You can make your own pH paper strips using a red cabbage indicator. Take filter paper (or coffee filter) and soak it in a co ncentrated red cabbage juice solution. After a few hours, remove the paper and allow it to dry (hang it by a clothespin or string). Cut the filter into strips and use them to test the pH of various solutions. To test a sample, place a drop of liquid on the test strip. Don't dip the s trip in the liquid because you'll get cabbage juice in it. An example of a basic solution is laundry soap. Examples of common acids include lemo n juice and vinegar. From < https://www.thoughtco.com/making-red-cabbage-ph-indicator-603650 > How will individual species and ecosystems respond as oceans become more acidic? Ocean acidification affects the ecosystems because they won't be able to as much coral making lots of fish and other creature s lose their homes. It also affects certain shellfish as they won’t be able to grow their shells. How can you identify if a solution is acidic? 2. If it is the color red on the pH scale, or if it goes under the number 7 on the pH scale. How can you identify if a solution becomes more acidic? 3. The lower the number on the pH scale. The solution will also taste sour as another indicator. What must occur in order for a solution to become more acidic? (HINT: a new substance has formed). 4. A precipitate or a chemical reaction must form/occur for a solutions to become more acidic Carbon dioxide (CO 2 ) and Ocean pH Unit 1 Climate Change Page 2

Recent estimates by scientists (Le Quere et al., 2012) have calculated that approximately 26% of all CO2 emitted from human -related activity was absorbed by the oceans during the decade 2002 - 2012. That's 2.5 billion gigatons of excess carbon that moved from the atmosphere into the ocean each year during that one decade. Some of this excess CO2 ends up in deep ocean currents that eventually upwell alo ng coastal areas bringing all that excess CO2with them and to oyster farms. Scientists have also observed that the oceans have become more acidic since the beginning of the Industrial Revolution. They project that this trend will continue in this century as indicated in the visualization pictured on the right. Scientists are concerned that oc ean acidification — a gradual acidification of seawater — could have negative consequences for marine organisms, marine food webs, and entire ecosystems. To better understand what ocean acidification is and why it happens, you will: Learn about pH chemistry in sea water Conduct a short experiment to investigate the relationship between increased CO 2 , acidity and pH Analyze and compare times series data sets of atmospheric CO2, sea surface CO2 and ocean pH Review: True or False Based on your understanding of the pH scale, which of the following statements are TRUE? ___ A neutral pH of 7 indicates that the concentration of (H+) ions is equal to the concentration of (OH -) ions. ___ The lower the pH, the higher the concentration of (OH-) ions compared to the concentration of (H+) ions. ___ The pH of an unknown solution changed from pH 5 to pH 4. This means that the concentration of (H+) ions increased by ten time s. ___ The lower the pH, the more acidic the solution. ___ Seawater is an acid. ___ The pH of seawater would become more acidic if the concentration of (H+) ions increased. ___ The pH of seawater since the Industrial Revolution has changed from 8.2 to 8.1. This means the concentration of (H+) ions has decreased. So far, you have learned that the concentration of CO 2 in the atmosphere is increasing and some of this extra CO 2 is dissolving in the oceans. But, can an increase in dissolved CO 2 change the pH of sea water? Unit 1 Climate Change Page 3

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