1 The Solubility of Calcium Carbonate Lesson Plan Developed by: John Thurmond, Plainfield North High School, Plainfield, Illinois Based on Presentation June, 2011. Northwestern University, Climate Change Curriculum Professional Development. Evanston, IL. Purpose The purpose of the following activity is: To calculate the solubility of a substance under a variety of temperatures. To construct a solubility curve based on experimental data. Overview A major factor affecting the solubility of a substance, that is, how much solute can be dissolved in a solvent, is temperature. A solubility curve demonstrates how the solubility of a substance varies with temperature. By determining the mass of solute that can be dissolved in a volume of solvent under a variety of temperatures, a solubility curve can be developed. In this lab exercise a solubility curve will be created for calcium carbonate, CaCO3. Student Outcomes The learning goals are for students to be able to: Explain the properties of calcium carbonate and how those properties affect solubility. Illinois State Science Standards STATE GOAL 11: Understand the processes of scientific inquiry and technological design to investigate questions, conduct experiments, and solve problems. 11.A.5a Formulate hypotheses referencing prior research and knowledge. 11.A.5e Report, display and defend the results of investigations to audiences that may include professionals and technical experts. The Solubility of Calcium Carbonate Teacher Overview Page 1 of 3
2 STATEGOAL 12: Understand the fundamental concepts, principles and Interconnections of the life, physical and earth/space sciences. 12.E.5 Analyze the processes involved in naturally occurring short- - - term and long- - - term Earth events (e.g., floods, ice ages, temperature, sea- - - level fluctuations). STATEGOAL13: Understand the relationships among science, technology and society in historical and contemporary contexts. 13.B.5b Analyze and describe the processes and effects of scientific and technological breakthroughs. Climate Literacy Essential Principles: 6. Human activities are impacting the climate system. (A,B,C) 7. Climate change will have consequences for the earth system and human lives. (D) Time One to two 50- minute class periods Level 10-12 th grade chemistry or environmental science. Materials and Tools balance four test tubes per group hot water baths 400 ml or 600 ml beaker, ring stand, test tube clamp, gas burner or alternative four thermometers per group 10 ml graduated cylinder spatula grease pencil test tube clamp test tube rack solid calcium carbonate distilled water graph paper Preparation Safety: Use caution when using the hot water bath to avoid hot water and steam burns. Prerequisites Students should have experience with stoichiometry and chemical reactions. The Solubility of Calcium Carbonate Teacher Overview Page 2 of 3
3 Background The concentration of CO2 in water is largely controlled by the atmospheric concentration of CO2 and temperature. Therefore the concentration of calcium carbonate in the ocean is highly correlated with temperature. Calcium carbonate also reacts with CO2 and water as described by the following equation: CO2+ H2O + CaCO3 Ca 2+ + 2HCO - 3 This means that the more CO2 dissolved in the water, the more readily the calcium carbonate will dissolve. CO2 is more soluble in cold pressurized water and less soluble in warm non- pressurized water. Therefore the concentration of CO2 is lower in shallow tropical waters, which reduces the solubility of the calcium carbonate, allowing corals to precipitate calcium carbonate skeletons in these conditions. Likewise, as ocean temperatures warm due to global climate change, the ocean will have a diminished ability to absorb CO2, including anthropogenic CO2. The Solubility of Calcium Carbonate Teacher Overview Page 3 of 3
Ocean Acidification Carbon Dioxide Is Putting Shelled Animals at Risk Shallow-water creatures, like these corals, are extremely vulnerable to carbonic acid. Scientists are calling for drastic measures to avert massive bleaching of the world's reefs. Photograph by Ove Hoegh- Guiderg/AFP/Getty Images For tens of millions of years, Earth's oceans have maintained a relatively stable acidity level. It's within this steady environment that the rich and varied web of life in today's seas has arisen and flourished. But research shows that this ancient balance is being undone by a recent and rapid drop in surface ph that could have devastating global consequences. Since the beginning of the industrial revolution in the early 1800s, fossil fuel-powered machines have driven an unprecedented burst of human industry and advancement. The unfortunate consequence, however, has been the emission of billions of tons of carbon dioxide (CO2) and other greenhouse gases into Earth's atmosphere. Scientists now know that about half of this anthropogenic, or man-made, CO2 has been absorbed over time by the oceans. This has benefited us by slowing the climate change these emissions would have instigated if they had remained in the air. But relatively new research is finding that the introduction of massive amounts of CO2 into the seas is altering water chemistry and affecting the life cycles of many marine organisms, particularly those at the lower end of the food chain. Carbonic Acid When carbon dioxide dissolves in this ocean, carbonic acid is formed. This leads to higher acidity, mainly near the surface, which has been proven to inhibit shell growth in
marine animals and is suspected as a cause of reproductive disorders in some fish. On the ph scale, which runs from 0 to 14, solutions with low numbers are considered acidic and those with higher numbers are basic. Seven is neutral. Over the past 300 million years, ocean ph has been slightly basic, averaging about 8.2. Today, it is around 8.1, a drop of 0.1 ph units, representing a 25-percent increase in acidity over the past two centuries. Carbon Storehouse The oceans currently absorb about a third of human-created CO2 emissions, roughly 22 million tons a day. Projections based on these numbers show that by the end of this century, continued emissions could reduce ocean ph by another 0.5 units. Shell-forming animals including corals, oysters, shrimp, lobster, many planktonic organisms, and even some fish species could be gravely affected. Equally worrisome is the fact that as the oceans continue to absorb more CO2, their capacity as a carbon storehouse could diminish. That means more of the carbon dioxide we emit will remain in the atmosphere, further aggravating global climate change. Scientific awareness of ocean acidification is relatively recent, and researchers are just beginning to study its effects on marine ecosystems. But all signs indicate that unless humans are able to control and eventually eliminate our fossil fuel emissions, ocean organisms will find themselves under increasing pressure to adapt to their habitat's changing chemistry or perish. This article is available online from National Geographic: http://ocean.nationalgeographic.com/ocean/critical- issues- ocean- acidification/
1 The Solubility of Calcium Carbonate Overview A major factor affecting the solubility of a substance, that is, how much solute can be dissolved in a solvent, is temperature. A solubility curve demonstrates how the solubility of a substance varies with temperature. By determining the mass of solute that can be dissolved in a volume of solvent under a variety of temperatures, a solubility curve can be developed. In this lab exercise a solubility curve will be created for calcium carbonate, CaCO3. Purpose The purpose of the following activity is: To calculate the solubility of a substance under a variety of temperatures. To construct a solubility curve based on experimental data. Safety Use caution when using the hot water bath to avoid hot water and steam burns. Equipment and materials balance four test tubes per group hot water baths 400 ml or 600 ml beaker, ring stand, test tube clamp, gas burner or alternative four thermometers per group 10 ml graduated cylinder scoopula grease pencil test tube clamp test tube rack solid calcium carbonate distilled water graph paper Procedure 1. Prepare a water bath by filling a large beaker approximately 2/3 full with water. Place the beaker on a ring stand above a gas burner and begin heating the water to just below boiling. While this is heating continue with Step 2. The Solubility of Calcium Carbonate Student Guide Page 1 of 3
2 2. Using a grease pencil, number your test tubes 1 through 4. 3. Copy the following table on the next page into your data book and fill it in with your own set of mass and volume data. Test Tube Mass CaCO 3 (g) used Volume Water (ml) Convert to g/100 ml Recrystallization Temp ( C) 1 2 3 4 4. Accurately measure out the following masses of solid calcium carbonate, placing the salt in the appropriate test tube. It is not necessary that you measure out exactly the masses given below, but you must record the precise masses you actually use. test tube 1: 2 grams CaCO3 test tube 2: 4 g test tube 3: 6 g test tube 4: 8 g 5. Add exactly 5.0 ml of water to each of the test tubes. 6. Place each of the tubes into the water bath in order to dissolve the solid CaCO3 in each test tube. You may find it necessary to use a stirring rod to help the dissolving process, particularly for test tubes 3 and 4. 7. Remove test tube 1 from the hot water bath once the CaCO3 has fully dissolved and place a thermometer in the tube. Watch the solution carefully. Record the temperature as soon as you see crystals forming within the test tube (you will need to wait awhile for crystals to form in this first test tube). 8. Repeat Step 6 for the other test tubes once the CaCO3 dissolves. Be prepared to act quickly for test tube 4 crystallization may occur very soon after you remove the test tube from the hot water bath. It may be necessary to return the test tube to the water bath to redissolve the salt and allow it to recrystallize again. The Solubility of Calcium Carbonate Student Guide Page 2 of 3
3 Results 1. Convert the mass/volume ratio you used for each test tube into mass/100 ml ratio. For example, in test tube 1 you had 2.0 g CaCO3 dissolved in 5.0 ml. This is equivalent to what mass of CaCO3 per 100 ml of water? 2. Record the temperature at which recrystallization occurred. This is the solubility of the substance at that temperature - the maximum amount of solute that can be dissolved in 100.0 ml of water at that temperature. 3. Using graph paper construct a solubility curve for CaCO3 based on your data. Conclusions and Questions 1. The line on your graph represents the concentration of a saturated solution of CaCO3 for various temperatures. Be sure to add values on both the X- and Y- axes. Connect your data points with a smooth curve. 2. Based on your solubility curve, predict the solubility of CaCO3 at the following temperatures: a. 50 C b. 70 C 3. Based on your solubility curve, would you best describe the following solutions as unsaturated, saturated, or supersaturated? a. 70 g / 100 ml H2O at 45 C b. 80 g / 100 ml H2O at 70 C c. 80 g / 100 ml H2O at 30 C The Solubility of Calcium Carbonate Student Guide Page 3 of 3