Effects of Acid Rain on Plants

Transcription

1 Environmental Chemistry Lab Effects of Acid Rain on Plants Acid precipitation is one of the effects of air pollution. When pollutants that contain nitrogen or sulfur react with water vapor in clouds, dilute acid forms. These acids fall to Earth as acid precipitation. Often, acid precipitation does not occur in the same place where the pollutants are released. The acid precipitation usually falls some distance downwind sometimes hundreds of kilometers away. Thus, the sites where pollutants that cause acid precipitation are released may not suffer the effects of acid precipitation. Coal-burning power plants are one source of air pollution. These power plants release sulfur dioxide into the air. Sulfur dioxide reacts with the water vapor in air to produce acid that contains sulfur. This acid later falls to Earth as acid precipitation. In this investigation, you will create a chemical reaction that produces sulfur dioxide. The same acids that result from coal-burning power plants will form. You will see the effects of acid precipitation on living things in this case, plants. OBJECTIVES Perform a chemical reaction that produces sulfur dioxide, a component of acid precipitation. Hypothesize the effects acids containing sulfur will have on plants. MATERIALS clear plastic bags, large (2) houseplants of the same type, potted (2) sodium nitrite, 2 g sulfuric acid, 1 M (2 ml) EQUIPMENT beaker, 50 ml twist tie or tape SAFETY Put on a lab apron, safety goggles, and gloves. In this lab, you will be working with chemicals that can harm your skin and eyes or stain your skin and clothing. If you get a chemical on your skin or clothing, wash it off at the sink while calling to your teacher. If you get a chemical in your eyes, immediately flush it out at the eyewash station while calling to your teacher. 103 Applied Science: Environmental Chemistry Labs

2 Procedure 1. Place 2 g of sodium nitrite in a beaker. Place a plant and the beaker inside a plastic bag. Do not seal the bag. CAUTION: Steps 2 4 should be carried out only under a fume hood or outdoors. 2. Carefully add 2 ml of a 1 M solution of sulfuric acid to the beaker. Immediately seal the bag tightly, and secure the bag with a twist tie or tape. CAUTION: Because this reaction produces sulfur dioxide, a toxic gas, the bag should have no leaks. If a leak occurs, move away from the bag until the reaction is complete and the gas has dissipated. 3. Seal the same type of plant in an identical bag that does not contain sodium nitrite or sulfuric acid. 4. After 10 minutes, cut both bags open while keeping the plants and bags under the fume hood. Stay at least 5 m from the bags as the sulfur dioxide gas dissipates. Keep the plants and bags under the fume hood. 5. Predict the effects of the experiment on each plant over the next few days. Record your predictions. 6. Observe both plants over the next three days. Record your observations in a data table like the one shown below. SAMPLE DATA TABLE Day Control plant Experimental plant 1 normal normal 2 normal slightly wilted 3 normal very wilted Analysis 1. Analyzing Models In what ways is this a realistic model of acid precipitation? 2. Analyzing Models In what ways is this experiment not a realistic simulation of acid precipitation? 104 Applied Science: Environmental Chemistry Labs

3 Conclusions 1. Examining Data How closely did your predictions about the effects of the experiment on each plant match your observations? 2. Drawing Conclusions What does this experiment suggest about the effects of acid precipitation on plants? Extension 1. Analyzing Models Would you expect to see similar effects occur as rapidly, more rapidly, or less rapidly in the environment? Explain your answer. 2. Building Models Acid precipitation is damaging to plants because the sulfur dioxide contained in the water vapor clogs the openings on the surfaces of plants and interferes with photosynthesis. What kind of a safe model would demonstrate the damaging effects of acid precipitation in the form of water vapor on plant photosynthesis? Would this model be a realistic simulation of acid precipitation? 105 Applied Science: Environmental Chemistry Labs

4 Environmental Chemistry Lab Effects of Acid Rain on Plants Teacher Notes TIME REQUIRED one 50-minute class period LAB RATINGS Teacher Preparation 2 Student Setup 3 Concept Level 2 Cleanup 3 Easy Hard SKILLS ACQUIRED Predicting Constructing Models Experimenting Collecting Data Organizing and Analyzing Data Communicating SCIENTIFIC METHODS Make Observations Students will observe the effects of a reaction that produces sulfur dioxide. Ask Questions Students will make predictions about the effects of acid precipitation on plant growth. Analyze the Results Analysis questions 1 and 2 ask students to analyze their results. Draw Conclusions Conclusions questions 1 and 2 ask students to draw conclusions from their data. MATERIALS (PER LAB GROUP) beaker, 50 ml clear plastic bags, large (2) houseplants of the same type, potted (2) sodium nitrite, 2 g sulfuric acid, 1 M (2 ml) twist tie or tape 103a Applied Science: Environmental Chemistry Labs

5 SAFETY CAUTIONS Students should wear a lab apron, protective gloves, and safety goggles at all times during this investigation. Before attempting this activity, become familiar with the material safety data sheet for sulfur dioxide. When working with caustic or poisonous chemicals, use extreme caution. Allow only your most mature students to handle these materials. Alternatively, you may wish to handle the chemicals yourself or perform the procedure as a demonstration. For this activity, it is essential that a functioning fume hood is used to safely remove the sulfur dioxide gas. A functioning eyewash station should be immediately accessible. Test the bags beforehand for possible leaks. Use only bags that are free of leaks. Sulfur dioxide is very poisonous. Keep students at least 5 m from the simulation for the duration of the reaction. Pour all leftover acid solution into a safe container, and neutralize it to a ph of 7 by adding a dilute base, drop by drop, before pouring the solution down the drain. 103b Applied Science: Environmental Chemistry Labs