On the 15th of February, the Erasmus group visited the CIIMAR (Centro Interdisciplinar de Investigações Marinha e Ambiental) of the University of Porto to know their facilities and to participate in an activity about the greenhouse gas effect, more specifically, an experiment about the acidification of the oceans and its consequences.
The ocean absorbs a significant part of the carbon dioxide (CO2) that is released into the atmosphere, including that produced by human activities.
The ocean therefore plays a key role in minimising the impact of this greenhouse gas on the climate. However, as it dissolves in water, carbon dioxide results in the production of carbonic acid that cause the water to become acidic.
Since the Industrial Revolution, the release of CO2 into the atmosphere has significantly increased, particularly in the last few decades, resulting in considerable acidification of the ocean. This increase in acidity impacts marine organisms, for example, it decreases the ability of organisms like microalgae, molluscs, crustaceans and corals to build their shells, carapaces and calcium carbonate skeletons.
It can also impact the physiology and reproduction of some organisms. These impacts can in turn have ecological implications, affecting marine food chains and biodiversity, as well as economic implications causing serious losses for the fishing industry.
This activity introduces students to the greenhouse gas effect demonstrating experimentally ocean acidification caused by the increase of carbon dioxide in the atmosphere. In order to understand the adverse effects of ocean acidification to marine organisms, we also propose students to verify the erosion of the calcium carbonate present in the skeleton and shells of marine organisms through its reaction with an acidic liquid solution. Depending on the complexity level adopted, this protocol can be used to teach Science to students aged 9-14, and covers Ocean Literacy Principle 3 “The ocean has a major influence on weather and climate”.
Materials
- One red cabbage
- pH colour scale (prepared as indicated below)
- Baking soda
- Vinegar
- Distilled water
- Marine shells (from mussels, oysters or clams)
- Two small plastic water bottles (one of 300 ml, another of 500 ml)
- Straws or any other flexible tube
- Plasticine
- Glass cups or beakers
- Lemon juice
Protocol
Preparation of the pH colour scale:
- Bring water in the pot to boil.
- Add the red cabbage cut into chunks to the boiling water.
- Remove from the boil when the water is dark purple. Leave to cool down and then sieve.
- Keep the cooking water in the glass container.
- Create a pH colour scale by adding necessary amounts of vinegar or caustic soda to 5 mL of red cabbage extract.
The red ones were the most acidic, and the yellow ones were the most basic waters.
Acidification of water induced by dissolution of CO2:
Experiment 1:
- Make a hole in the lid of each plastic bottle and connect the two bottles by passing a straw through the holes made. Use the plasticine to seal the holes (make sure the bottles are well sealed so that exchanges of gas occur only through the straw).
- Add 30 ml of red cabbage extract plus 60 ml of distilled water to the small plastic bottle.
- Add 100 ml of vinegar to the bigger plastic bottle plus one teaspoon of baking soda. The acetic acid of the vinegar will react with the baking soda releasing CO2 (chemical reaction: CH3COOH + NaHCO3 -> CH3COONa + H2O + CO2(g)). The CO2 will diffuse through the straw to the smaller bottle lowering the pH of the solution.
- Observe the colour change occurring in the smaller bottle. Shake the bottle if needed. Compare the colours obtained with the pH colour scale. Make note of the changes observed and of the pH of each solution.
Experiment 2:
- Add equal volumes of red cabbage extract (15 ml of the cooking liquid + 30 ml of distilled water) to two glass containers or beakers.
- Use a straw to blow for about 30 to 60s on the test liquid of one of the beakers in order to create bubbles in the solution.
- Compare the changes in colour observed with the liquid on the second (untouched) beaker and with the pH colour scale.
- Make a note of the observations and pH.
Effects of ocean acidification on the shells of marine organisms:
- Add to a glass 15 ml of the red cabbage extract and 30 ml of lemon juice. Note: the resulting solution should be dark red (pH<3).
- Add to another glass 15 ml of the red cabbage extract and 30 ml of tap water.
- Place a shell in each of the glasses and observe the release of CO2.
Results
In the other experiment (Effects of ocean acidification on the shells of marine organisms), we used two glasses, one of them with a straw to blow for about 30 to 60s mixing the CO2 with the solution to become acidic.
We used a shell, to see the effects of ocean acidification on marine species and we put a shell in each glass.
The calcium carbonate in the shell that was in the more acidic solution started to dissolve , showing us the effects of acid water in marine species. In the other glass nothing happened because the water wasn't acidic.
In conclusion, acid water is a big problem , since it can destroy the protection of some animals.
Discussion of results
1. Indicate the hypothesis tested in each experiment.
The accumulation of CO2 in the sea waters turns the ocean more acidic.
2. Indicate the colour changes and respective pH observed in experiments 1 and 2 related of Acidification of water induced by dissolution of CO2.
3. What was the origin of the CO2 causing acidification in experiment 2?
The CO2 occurred from our exhalation through the straw which acidified the solution.
4. Indicate why did you need the second (untouched) glass in experiment 2. How would you call it in your experimental design?
This second glass (untouched) is called control, and it is used to compare the final results.
5. In which glass did you observe the most release of CO2 in the experiment related to the effects of ocean acidification on the shells of marine organisms?
The glass which we observed the most release of CO2, was where the fluid was red (lower pH), and consequently, it was possible to see the dissolution of the calcium carbonate of the shells.
6. Indicate three human activities that cause an intense release of CO2 into the atmosphere contributing to ocean acidification.
The combustion of fossil fuel, like in planes, ships, industrial works and bushfire.
Authors: João Pedro Ribeiro, Helen Victoria, Vasco Lemos, Katrina Sapnova, Duarte Santos, Javier Bueno; Pedro Soares, Daniel Nunez, Juliana Soares, Viviane Dune, Inês Oliveira, Charlotte Salomon, Yuri Santos, Daniel Quero, Miguel Silva, Niccoló Pavone, Beatriz Pires, Sofia Almeida, Daniela Ulmane and Letícia Seixas.