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Something about CALCIUM CARBONATE IN NATURE A lab activity for more than a purpose: it can be used as: 1. an example of a chemical reaction 2. a way to tell the composition of many specimens 3. a mean for considering common aspects of different features in nature 4. introduction to the study of rocks 5. an introduction to part of the rock cycle 6. a mean to learn many words used in everyday English, not only in science What you need: materials list Some calcium carbonate from the lab A dropper and some diluted hydrocloric acid Some flour / talc / white powder of some sort and samples of rocks and hard mineral parts of many organisms, as in the following pictures Minerals Sedimentary rocks Calcite aragonite black-limestone Metamorphic rocks marble ..ait limestone Stalactite travertine ..in Alabaster or stalagmitic limestone coral-reef Sea urchins (Echinodermata) algae Mollusks shells Foraminifera Vertebrates skeletons: (10%....) Egg shell What to do: directions Drop some acid on each object, starting with calcium carbonate and flour Results: observe what happens • Positive control test with calcium carbonate: under the action of hydrocloric acid a bubbling release of gas takes place • Negative control test with white powder: no release of gas • Positive test for minerals and rocks shown in the pictures with the exception of vertebrates skeletons Results discussion 1 What Causes the Fizz? CaCO3 + HCl CO2 + H2O + Ca++ + Cl- On the left side of this reaction calcium carbonate CaCO3 is in contact with hydrochloric acid (HCl). These react to form carbon dioxide gas (CO2), water (H2O), dissolved calcium (Ca++) and dissolved chlorine (Cl-). The carbon dioxide bubbles that you observe are evidence that a reaction is taking place. When that occurs, calcium carbonate is present. http://geology.com/minerals/acidtest.shtml website The "Acid Test" for Carbonate Minerals and Carbonate Rocks Results discussion 2 Specimens which react as the CaCO3 sample are composed very likely of that compound. Or: How to recognize calcium carbonate The bubbling release of carbon dioxide gas tells us that…. Results discussion 3 3 - a mean for considering common aspects (CaCO3) belonging to different features in nature Results discussion 4, 5 • 4 an introduction to the study of the genesis of rocks • 5 an introduction to part of the rock cycle Results discussion 6 6 - a mean to learn many words used in everyday English, not only in science: coral reef, sea urchins, marble, limestone……. Students and teacher will look for “A little text for each specimen”