Water Planet Challenge

Electrically Speaking: Acid Bath! - High School

Introduction

Students often have preconceptions about how their actions can and do effect the environment. This lesson is focused on the way that human use of natural resources impacts the atmosphere and in turn the waters of the Earth, in particular the oceans. The ocean is the feature of the Earth that makes it a unique place where humans and other organisms can live. Since the Industrial Revolution humans have been using fossil fuels to provide for their energy needs. Burning fossil fuels release carbon dioxide into the atmosphere, and it has been absorbed by the oceans for the last two centuries changing the pH of the water. The previous lesson examined the physical and chemical effects of the addition of anthropogenic carbon on the oceans. This lesson will examine the effect of increasing acidity on the shells of organisms. Even the slightest changes in the ocean in turn have impact on the environment, biodiversity and human population.

Objectives

• Describe how everyday human activities produce pollutants that can be measured.
• Measurements of pollutants are used to determine the affect they have on the planet and the health of organisms on the planet.

Materials

• Computer with Internet access
• Library and/or classroom resources
• Science journal
• Sea shells (5 or 6 per group)
• Water
• Hydrochloric Acid (HCl)
• pH paper or pH meter
• Plastic cups or containers
• Electronic Balance
• Sand (optional)

Vocabulary

• global warming –refers to an average increase in the Earth's temperature over time
• climate change – a result of the overall average increase in the Earth’s temperature. This term encompasses all changes to the Earth’s climate, ecosystems, human health and society.
• anthropogenic carbon- carbon emitted to the atmosphere due to the activities of man and closely linked to current changes in the climate..
• environment – the habitats surrounding an area
• acidification – ongoing decrease in the pH of the Earth's oceans
• CO2– carbon dioxide, the primary greenhouse gas Carbonization
• carbon cycle - the biogeochemical cycle by which carbon is exchanged between the biosphere, geosphere, hydrosphere, and atmosphere of the Earth.
• atmosphere – the layer of gases surrounding the Earth
• hydrosphere – the waters of the Earth
• biosphere- all regions of the Earth environs that house life.
• solubility - is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a liquid solvent to form a homogeneous solution

Teacher Background

The ocean is an open system that receives energy from the sun and carbon dioxide from the air. The oceans are becoming more acidic because carbonic acid forms when carbon dioxide dissolves in water. The oceans are warming because carbon dioxide in the air is a greenhouse gas that causes the air to hold more heat. That in turn causes the oceans to release less heat to the air. Increasing acidity and temperature are just two of the changes our oceans are experiencing. More specifically, when carbon dioxide (CO2) reacts with seawater lowering the pH, it also reduces the availability of carbonate ions which play an important role in shell formation of marine organisms such as corals, marine plankton, and shellfish. This phenomenon is commonly called ocean acidification. The acid causes erosion of the shells and coral skeletons and there is less calcium available for organisms to build new shells. This happens because a secondary reaction decomposes the calcium carbonate in shells to produce bicarbonate ions (HCO3-). This process acts as a slight buffer against acidification by absorbing excess hydrogen ions, but at a cost to living systems. The buffering effect is slight and diminishes as the acidification increases. Scientists are still building a model incorporating all these variables in order to better understand the extent of the impacts anthropogenic carbon from the burning of fossil fuels has on our oceans living systems.

Some of the smaller calcifying organisms are important food sources for higher marine organisms resulting in disruption of food chains. Declining health in coral reefs due to increases in temperature and decreases in carbonate ion would have negative impacts on tourism and fisheries. Abundance of commercially important shellfish species may also decline and negative impacts on finfish may occur. This rapidly emerging scientific issue and possible ecological impacts have raised serious concerns across the scientific and fisheries resource management communities.

The effects of this increasing pH can have multiple effects on life in the ocean. True the algae and sea plants may benefit from increased CO2, using it for photosynthesis. The animal life can be affected several different ways. The creation of carbonic acid is dissolving the shells of shell fish and corals that are made of calcium carbonate. The acid is also reducing the available molecules these animals use to build their shells. Studies are also being conducted concerning the effect of lower pH on the reproduction rates of sea urchins, oysters and corals. In the event that these organisms die out it will disrupt the marine food chains and human fisheries.

Additional sources:
Measuring and monitoring the amounts of CO2 mixing in the oceans: http://www.oar.noaa.gov/research/2007/ocean_acidity.shtml
Explaining the chemical interactions of CO2 once it has entered the oceans:
http://coralreefwatch.noaa.gov/satellite/oa/description/oaps_intro_oa.html
Coral reefs are affected by ocean acidification:
http://www.usgs.gov/newsroom/article.asp?ID=1847
http://oceanacidification.wordpress.com/2011/01/17/coral-reef-conservation-ocean-acidification/
Corals are under a double threat, acidification and increased temperature. Though higher temperatures may return some of the dissolved CO2 to the atmosphere, the increased temperatures cause coral bleaching:
http://www.climatewatch.noaa.gov/2010/articles/hope-in-the-face-of-a-caribbean-coral-crisis
http://www.stanford.edu/group/microdocs/coralbleaching.html
For basics on corals:
http://pbs.bishopmuseum.org/Oman-coral-book/Chap1/CorBkCh1.htm
Ocean Acidification: A National Strategy To Meet the Challenges of a Changing Ocean, Committee on the Development of an Integrated Science Strategy for Ocean Acidification Monitoring, Research, and Impacts Assessment; National Research Council, 175 pages, 2010
This is report from the National Research Council of The National Academies that summarizes the current research on this entire topic.

Engage

Ask students to look at the 3 maps and make observations. Based on the information provided in the maps what would they predict the conditions would be when they are 80 years old? How does the failure of the coral reef habitat impact your lifestyle?

Caption: The three maps show model data of how the availability of calcium carbonate is predicted to decrease over the next century at a depth of 10 meters in the ocean—where most corals occur. Blue indicates surface waters are sufficiently saturated with calcium carbonate; organisms have enough material to build their protective shells. Areas that are deep red are expected to be sufficiently acidic to dissolve shell-building organisms. Graph based on models by James Orr of the Laboratory for the Sciences of Climate and Environment in Paris. Image courtesy of the NOAA Environmental Visualization Laboratory. http://www.climatewatch.noaa.gov/2009/articles/an-upwelling-crisis/2

Explore

Ask students: Have you ever noticed the lifeguard at the pool testing the water every hour? Or have you ever had an aquarium that required checking the water? One of the factors they are checking is the pH of the water.

Review with students the pH scale. The scale ranges from 0 to 14 with 7 being neutral. Water that measures below 7 is more acidic, while above 7 is more basic or alkaline. The natural pH of water is considered to be 7, though that is not always true. Explain to students that ocean water is normally slightly basic. Refer to the last activity when they tested the pH of different water samples, and explain that increased carbon dioxide is causing ocean water to have a lower pH or to become more acidic.

Ask what could happen in a pool or aquarium if the pH was too acidic or too basic? Answers will vary: the animals will die, it will burn their skin, they will not be able to see.

Help students review the ways the pH of water can be changed. Remind them that the of burning fossil fuels has increased the amount of carbon dioxide released into the atmosphere and oceans.

Testable Questions
How does more acidic water affect ocean animals with calcium carbonate shells or skeletons? How does the presence of shelled organisms in turn affect ocean water?

Materials

• science journal
• sea shells (try to make them of a similar species and size 5 to 6 per group), thin shells work well or carbonate sand, if available
• water
• hydrochloric acid (dilute by adding 1M HCl to the distilled water to a pH of 6, 5,4,3)
• clean plastic cups or containers
• pH paper strips or pH meter
• tongs
• sand

Procedures

1. Draw, label, and make observations of each seashell, include mass, color, size, thickness, strength
(Students can place a book on top of the shell to determine the strength and other measurements.)
2. Label the cups or containers with the strength of the solution to be used.
3. Place a shell into each container or a predetermined amount of sand. Be sure each containers is labeled with the correct pH.
4. Make different strengths of acid solutions (pH 7, pH 6, pH 5, pH 4, pH 3). Using distilled water and
a pH meter add dilute 1M HCl one drop at a time until the pH paper or meter registers the desired pH.
5. In each respective container with a shell, pour enough solution to cover each shell.
6. Pour 200 ml of each solution into the corresponding cup covering the shells. If 200 ml does not cover the shells, more solution should be added but remember to add the same amount to each container.
7. Set the remainder of the acid solutions aside for testing at the end of the experiment.
8. Record new observations of the shells and the water during the period. Keep the shells in the solutions.
9. Allow the shells to sit in the solution for a day or more.
10. Using tongs, remove each shell from the container for observations. Repeat the set of observations you made in step 1 on the shells that have now been soaking in the acid solutions.
11. Test and record the pH of the remaining liquid from the original solutions and each solution that contained the shells.

Side Bar on safety
Goggles are required to work with HCl.

The teacher should prepare the HCL solutions for the students.
How to make dilute acidic water. Note always add acid to water.
How to make the solutions using distiller water ( pH of 7), 1M HCl ( pH of 0) and a graduated cylinder.

A HCl solution with a pH of 3 is a .001M HCL solution.
1. To make a .001 HCl solution, pour 90 ml of distilled water into graduated cylinder and add 10 ml of 1M HCL , now it is .1M HCl
2. Pour 90 ml of distilled water into a graduated cylinder, add 10 ml of the .1M HCl, now it is .01M HCl with a pH of 2
3. Pour 90 ml of distilled water into a graduated cylinder, add 10 ml of the .01M HCl, now it is .001M HCl with a pH of 3.

A HCl solution with a pH of 4 is a .0001M HCL solution
1. Pour 90 ml of distilled water into a graduated cylinder, add 10 ml of the .001M HCl, now it is .0001M HCl with a pH of 4.

A HCl solution with a pH of 5 is a .00001M HCl solution.
1. Pour 90 ml of distilled water into a graduated cylinder add 10 ml of the .0001M HCl, now it is .00001M HCl with a
with a pH of 5.

A HCl solution with a pH of 6 is a .000001M HCl solution.
1. Pour 90 ml of distilled water into a graduated cylinder add 10 ml of .00001M HCl now it is a .000001M HCl solution with a pH of 6.
These amounts can be multiplied to make larger amounts.

Analysis

1. Why was it important to set aside samples of the original solutions? This is a control that will allow us to see if the shells affected the pH of the solutions, and not that the changes are due to time. Hydrochloric acid will off gas, resulting in an increase in pH over time. The students need to assess if the shells also affect the pH of the solutions.
2. Using evidence from the experiment explain what is the effect of the acid on marine animals with hard shells? Answers may include: Marine animals with hard shells depend on calcium carbonate to make their shells. As the oceans become more acidic, their shells become less massive, thinner and weak. They should support their answer with data from their investigation.
3. Using evidence from this experiment, what is the effect of marine animals with hard shells on the water they live in? Answers may include: Marine animals with hard shells slightly reduce the acidification of the oceans. They should support their answer with data from their investigation.

Explain

Show the video from American Museum of Natural History - Acid Oceans
This 6-minute video is about an experiment scientists are conducting concerning the effect of ocean acidification on sea urchins.

If you’re an ocean creature with a hard shell—like a sea urchin, hermit crab, or coral polyp—you prefer ocean water with a pH of about 8.2. This chemistry makes it easy to assemble your armor from carbon-based building blocks dissolved in the ocean. Since the industrial age, though, the ocean’s pH has become more acidic from absorbing the greenhouse gas carbon dioxide from the air, dropping to 8.05 on average. Biologists like Gretchen Hofmann are realizing that this tiny change is hampering the development of hard-shelled marine life, leaving it more vulnerable to environmental stressors.

Adapted from http://www.amnhblogs.org/content/science-bulletins-acid-oceans

1. Using evidence from the experiments you have performed explain where is the carbon dioxide in the ocean is coming from and how has the CO2 absorbed by the ocean changed its chemistry (products, pH)?
(Answers may include: The increase in carbon dioxide has decreased the ocean’s pH from 8.2 to 8.05 on average, making it more acidic because when CO2 dissolves in water it also reacts with water to form H+ and HCO3- ions. The free H+ then reacts with carbonate ions in ocean water to form more HCO3-. The result is less CO3- ions which are required to form shells or CaCO3 )
2. Once the acid has formed in the water, what does it do to shells and what do the shells in turn do to the water? Give the inputs and outputs and processes involved.
Calcium carbonate (CaCO3) dissociates to form calcium ions (Ca++) and carbonate ions (CO3-). These carbonate ions combine with the free hydrogen ions (H+) to form bicarbonate ions (HCO3+)This can result in a slight buffering at higher pH levels.

Students may read this article to help answer this question.
http://www.epa.gov/acidrain/effects/surface_water.html#a2
3. Describe what effect increasing acidification of ocean water can have on animal species? Answers will vary: Burn their skin, dissolve their shells and skeletons, kill their food sources.
4. Using evidence from the experiment and research, elaborate on what impact a more acidic ocean can have on the ocean food web? Describe the consequences in detail using an actual food web. Answers may include: The warming and acidified ocean would impact organisms, such as shrimp, lobsters, crabs, clams, oysters and coral, which depend on calcium carbonate to develop their shells. Changes in the size or abundance of these organisms would affect the humans and marine life that depend on them for food. Students who do deeper research will reveal information on: the interference of acidification on the rate of photosynthesis; the reduction in growth of marine organisms at the base of the food chain that in turn will negatively impact commercial marine food products; even a potential increase in ocean noise. Secondarily, a reduction in shell fish populations would result in loss of livelihood. More developing nations would be negatively impacted by this which could lead to destabilization in already vulnerable regions. Students should support their research with sources and specific examples.

Evaluate

Explain how your use of electricity is causing stress to ocean animals. Use evidence you have collected in the other activities fro this website. How we use electricity, how we produce electricity, the emissions burning fossil fuels releases into the atmosphere, and how the ocean plays a part in cleansing the atmosphere, to the effect on ocean ecosystems.

Elaboration
Students may make salt water and compare the effect on shells in fresh verses salt water.
Students may test the difference effects of acid on shells in water of different temperatures.

Share the following diagram with students. Ask them to use the diagram to explain how the carbon cycle is involved in the problem of ocean acidification.

Additional websites:
http://www.climatewatch.noaa.gov/2009/articles/an-upwelling-crisis
http://www.climatewatch.noaa.gov/2009/videos/origin-and-impacts-ocean-acidification2
http://www.climatewatch.noaa.gov/2009/videos/origin-and-impacts-ocean-acidification-part-3
http://www.myfootprint.org/
http://www.pmel.noaa.gov/co2/OA/OA2.jpg
http://www.pmel.noaa.gov/co2/OA/A_Sea_Change_Excerpt.mov

LS Core Idea 3:Organisms and populations of organisms obtain necessary resources from their environment which includes other organisms and physical factors. [Ecosystems: Interactions, Energy, and Dynamics] Grades 9 – 12
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LS3.C: Ecosystems Dynamics, Stability, and Resilience
Sub-question: What happens to organisms and ecosystems when there are changes in the environment? Ecosystems dynamics can result in changes in the number and types of organisms and the survival, migration, and extinction of species.
How do ecosystems change?
A complex set of interactions within an ecosystem can maintain the numbers and types of organisms in an ecosystem that is relatively constant over long periods of time.
The number of organisms in ecosystems fluctuates over time. Extreme fluctuations in size of populations challenge the stability of ecosystems in terms of resources and habitat availability.
If a biotic or abiotic disturbance to an ecosystem occurs, the affected system may return to being similar to the original system (that is, the ecosystem is resilient), or become a very different ecosystem.
Anthropogenic changes in the environment such as changes in climate, migration by an invasive species, and over-exploitation can impact the stability of an ecosystem.
LS Core Idea 4: Biological evolution explains the unity and diversity of species. [Biological Evolution: Unity and Diversity]
LS4.D: Biodiversity and Humans
Sub-question: What is biodiversity and how do humans affect it and how does it affect humans? What is the current threat to biodiversity given human impact? How will changes in biodiversity affect humans? Humans depend on the living world. The resources and benefits provided by the living world are considered “ecosystem services.”
Biodiversity is seriously threatened by human impact in the form of habitat destruction, over-exploitation, damage by invasive species, and climate change. These have the potential to cause a major pulse of biological extinctions.
Biological extinction is a critical factor in reducing biodiversity because it is irreversible.
Sustaining biodiversity so productivity and ecosystem functioning remain is essential to maintaining and enhancing the quality of life of the growing human population.
Physical Science (PS) Core Idea 1: Macroscopic states and characteristic properties of matter depend on the type, arrangement and motion of particles at the molecular and atomic scales. [Structure and Properties of Matter]
PS1.B: Properties of Matter
Sub-question: How can you distinguish one substance from another? All substances have characteristic measurable properties that depend on the conditions under which they are observed. These properties depend on atomic substructure but do not persist at the atomic level.