SIDE DISPLAY Acid Rain Eats Stone! Visitors drip sulfuric acid onto one piece of chalk and water onto another piece of chalk and observe the results. OBJECTIVES: Visitors learn the composition of acid rain. They learn how acid rain can react with and affect certain structures. SCIENCE TOPICS PROCESS SKILLS VOCABULARY Chemical Reactions Environmental Pollutants Observing Investigating Controlling Variables Acid Chemical Reaction Pollutant Unit 4 Environmental Chemistry U4.57
Acid Rain Eats Stone! To do and notice: 1. Create a fresh surface on a piece of chalk by rubbing it on one of the stone bunnies 2. Squeeze 1 drop of sulfuric acid solution (H 2 SO 4 ) onto the piece of chalk 3. Squeeze 1 drop of water (H 2 O) onto another piece of chalk that has been roughed up. 4. Watch both drops carefully. Use the magnifying glass to look closely. Which drop reacts with the surface of the chalk and begins to bubble? What is going on? Acid rain is composed primarily of dilute sulfuric acid (H 2 SO 4 ) and dilute nitric acid (HN0 3 ). These acids are formed from the gases sulfur dioxide (S0 2 ) and nitrogen dioxide (NO 2 ). Both gases are pollutants emitted by smokestacks and tailpipes. Acid rain affects both living and nonliving things. Chalk, concrete, and marble contain calcium carbonate (CaCO 3 ). When either of the two acids comes in contact with calcium carbonate, it reacts to form carbon dioxide (CO 2 ), water (H 2 O), and a salt. The bubbles you see are carbon dioxide gas. The simulated acid rain will gradually cause the chalk to crumble into the gravel. The concrete bunnies show what happens to a statue exposed to acid rain. 2007 OMSI
U4.58 Unit 4 Environmental Chemistry
Side Display: Acid Rain Eats Stone! Operating Guide See Materials Prep for more details (with amounts to have on hand) Two 30-ml dropper bottles One 9 x 12-inch Pyrex baking dish One large, resealable plastic storage bag Two small concrete bunnies or other animal statues (available at a garden supply store) Several small pieces of blackboard chalk (keep one box on hand) 15-20 ml 1M H 2 SO 4 (sulfuric acid) (keep 200 ml on hand) OR 28 ml 18M (concentrated) H 2 SO 4 (keep 100 ml on hand) One 100-ml graduated cylinder One 500-ml plastic bottle One 600-ml beaker One glass stirring rod Setup/Takedown Procedures Fill the baking dish with one inch of gravel or sand. Place the bunnies on top of the gravel, toward the back of the dish. Break two or three chalk pieces in half and place them on the gravel, near the front of the dish. Label the two 30-ml dropper bottles Water (H 2 O) and 1M (Sulfuric Acid (H 2 SO 4 ). Fill the dropper bottles with the appropriate solutions. Set out the dish, dropper bottles, and public copy. Replace the chalk pieces as needed. Refill and relabel the dropper bottles as needed. This setup can be reused indefinitely. At the end of the week, return it to Unit 4 storage. Unit 4 Environmental Chemistry U4.59
Side Display: Acid Rain Eats Stone! Operating Guide In time, after reacting with sulfuric acid, the concrete bunnies will form a layer of CaSO 4 (calcium sulfate). If a visitor then tries to drop acid onto the bunnies, the reaction will not be obvious. You can explain this by describing the protective layering and add that the acid is still doing damage just at a slower rate. You can relate this to what happens with marble buildings or statues when they are exposed to acid rain. H 2 SO 4 (sulfuric acid) is a hazardous substance; follow the handling and disposal instructions. Consult the Material Safety Data Sheets (MSDS) for additional information. CAUTION: Concentrated (18M) H 2 SO 4 (sulfuric acid) is extremely corrosive. Handle it with care. Wear protective gloves, an apron, and eyewear. Use it only in the fume hood. Avoid contact with skin or clothing. Neutralize any spills with baking soda and clean up with large amounts of water. CAUTION: A large amount of heat will be evolved after you mix the H 2 SO 4 with water. Do not handle the beaker until it has cooled. To make 1M H 2 SO 4 (sulfuric acid): Turn on the fume hood. Wear protective eyewear, chemical safety gloves, and an apron or lab jacket. Fill the 600-ml flask with 472 ml of dh 2 O (deionized water) and place it in the fume hood. In the fume hood, measure 28 ml of concentrated (18M) H 2 SO 4 (sulfuric acid) into a 100-ml graduated cylinder. SLOWLY add the acid to the water and stir the solution with a glass rod Store the solution in a labeled/dated 500-ml plastic bottle in the acid cabinet. Turn off the fume hood. U4.60 Unit 4 Environmental Chemistry