Transcript Acid Rain
Yr 10 Chemistry Environmental Chemistry: Acid Rain Starter Which is the odd one out? Give reasons for your answer car volcano house Objectives TO KNOW what is ‘acid rain’. TO BE ABLE to write the balanced equations for the formation of acid rain and its reaction with limestone. TO UNDERSTAND how acid rain leads to environmental damage. Acid Rain Mind Map Definition Prevention ACID RAIN Affects of Acid Rain Animals Plants Building Humans Gases that cause Acid Rain Chemical reactions on building materials Chemical reactions to form acid rain Man made sources Acid Rain Mind Map What to include: Definition Gases Man-made sources Chemical Reactions Affects of Acid Rain. Plants/Animals/Humans/Buildings Chemical reactions on Building Materials Prevention References (on the back) Rates of reaction: Why does more concentrated acid in rain have a greater effect. Rates of reaction: Why does large building blocks of building materials appear to be affected less than small blocks. Environmental Chemistry What is it? • encourages environmentally conscious behaviour • reduces and prevents pollution • reduces the destruction of the planet Basics • • • • • • • • • • • better to prevent waste than to treat it afterwards aim for maximum atom economy use processes which require fewer chemicals don’t make products that are toxic to human health don’t make products that are toxic to the environment reduce the energy requirements of processes use alternative energy resources use renewable raw materials, not finite resources use catalysts where possible waste products should be designed to be biodegradable reduce the risk of explosions and fires Man affects the Earth in many ways. These are just some of the ways we have an effect on the Earth •Burning fossil fuels – acid rain, global warming •Open cast mining •Disposal of waste technology (mostly sent overseas) •Disposal of household waste (incineration or landfill) •Extraction of oil •Sea bed mining •Extraction of salt from the sea Contents Definition Causes Formation Effects Preventive Measures Definition of Acid Rain Precipitation that has a pH of less than that of natural rainwater (which is about 5.6 due to dissolved carbon dioxide). It is formed when 1. sulfur dioxide and sulfur trioxide 2. nitrogen monoxide and nitrogen dioxide 3. Carbon dioxide gases in the atmosphere, combine with water vapor and precipitate as sulfuric acid or nitric acid. This acidic precipitation then falls to the earth as rain, snow, or fog. Formation of Sulfuric Acid (H2SO4) 2SO2(g) + O2(g) 2SO3(g) SO3(g) + H2O(l) H2SO4(aq) Formation of Nitric Acid (HNO3) 2NO(g) + O2(g) 2NO2(g) 4NO2(g) + 2H2O(l) + O2(g) 4HNO3(aq) Sources OF ACID RAIN SO2 NOX Sources of Acid Rain Natural Sources – Non-anthropogenic (not man-made) Emissions from volcanoes and from biological processes that occur on the land, in wetlands, and in the oceans contribute acidproducing gases to the atmosphere Effects of acidic deposits have been detected in glacial ice thousands of years old in remote parts of the globe Anthropogenic Sources of Acid Rain The principal cause of acid rain is from human sources Industrial factories, power-generating plants and vehicles Sulfur dioxide and oxides of nitrogen are released during the fuel burning process (i.e. combustion) Sulfur dioxide accounts for about 90 % of all acid rainfall MSN Encarta Formation of Acid Rain Formation of Acid Rain When water vapor condenses, or as the rain falls, acidic gases dissolve in the water to form sulfuric acid (H2SO4) and nitric acid (HNO3). While the air in cleaned of these acidic pollutants in this way, the resulting precipitation is acidic, and it can have serious negative effects. Acidic Rain Deposition • Acidic particles and vapors are deposited via two processes - wet and dry deposition. 1. Wet deposition is acid rain, the process by which acids are removed from the atmosphere in rain, snow, sleet or hail. 2. Dry deposition takes place when particles such as fly ash, sulfates, nitrates, and gases (such as SO2 and NO), are deposited on, or absorbed onto, surfaces. • The gases can then be converted into acids when they contact water. Harmful Effects of Acid Rain Harmful to aquatic life Increased acidity in water bodies Stops eggs of certain organisms (e.g. fish) to stop hatching Changes population ratios Affects the ecosystem Effects on Aquatic Life Acidification of lakes and rivers. One major effect on fish is the increased concentration of Al ion resulting from the leaching of soil by acid rain. Al ion affects the function of the gills. Effects of Vegetation Harmful to vegetation Increased acidity in soil Leaches nutrients from soil, slowing plant growth Leaches toxins from soil, poisoning plants Creates brown spots in leaves of trees, impeding photosynthesis Allows organisms to infect through broken leaves Effect on soil and vegetation Acute injury due to short term exposure to high acid concentrations leads to attacks on cells producing dead areas of leaves which dry out and usually become bleached. Chronic injury due to long term exposure to even low acid concentrations disrupts chlorophyll synthesis, characterized by yellowing of leaves. Acid rain also leaches or removes important nutrients such as magnesium ion from soil. http://abacus.bates.edu/~ganderso/biology/bio270/clover_leaf_bu rns_pH2_30d.gif MSN Encarta Effects of Acid Rain on Buildings and Structures Marble is particularly susceptible Accelerates weathering in metal and stone structures Eg. Parthenon in Athens, Greece; Taj Mahal in Agra, India MSN Encarta http://www.lauraknauth.com/photos/france/thinker.jpg Effects on Materials So the sulfate can dissolve in water leading to considerable damage to structural and artists’ stone and this is called ‘stone leprosy’ Corrosion of iron and steel Acid rain pollution causes bleaching and weakening of fabrics and leather discoloration and embitterment of paper. Leach heavy toxic metals such as lead, cadmium and mercury into the water system. Effects of Acid Rain on Human Health Affects human health Respiratory problems, asthma, dry coughs, headaches and throat irritations. Eye Irritation Leaching of toxins from the soil by acid rain can be absorbed by plants and animals. When consumed, these toxins affect humans severely. Brain damage, kidney problems, and Alzheimer's disease has been linked to people eating "toxic" animals/plants. Effect on Visibility The mist of sulfuric acid and sulfate aerosols in the atmosphere can cause great loss of visibility and can curtail air flights. Controlling Acid Rain Most efforts at reducing acid rain are directed at the important sources of the pollutants, namely the burning of coal and the fuelling of automobile engines. Preventive Measures Reduce amount of sulfur dioxide and oxides of nitrogen released into the atmosphere Use less energy (hence less fuel burned) Use cleaner fuels Remove oxides of sulfur and oxides of nitrogen before releasing Flue gas desulphurization Catalytic Converters Preventive Measures Use cleaner fuels Coal that contains less sulfur "Washing" the coal to reduce sulfur content Natural Gas Preventive Measures Flue Gas Desulfurization (FGD) Removes sulfur dioxide from flue gas (waste gases) Consists of a wet scrubber and a reaction tower equipped with a fan that extracts hot smoky stack gases from a power plant into the tower Lime or limestone (calcium carbonate) in slurry form is injected into the tower to mix with the stack gases and reacts with the sulphur dioxide present Preventive Measures (continued) Produces pH-neutral calcium sulfate that is physically removed from the scrubber Sulfates can be used for industrial purposes Scrubber at work MSN Encarta Alkaline Scrubbers Preventive Measures Use sources other than coal to generate electricity • nuclear power • hydro-electricity • wind energy • geothermal energy, • solar energy Issue of cost http://upload.wikimedia.org/wikipedia/commons/4/4e/Nuclear_Power_Plant_Cattenom.jpg Reducing the effects of Acid Rain Liming Powdered limestone/limewater added to water and soil to neutralize acid Used extensively in Norway and Sweden Expensive, short-term remedy Activity: Show the balanced chemical equation for the reaction with acid and calcium carbonate (limestone) Problem Scenario Suppose you worked in the government. A company wants to set up a factory in your country. It would bring jobs, but it would also bring about pollution, which would lead to acid rain. Would you allow it? Justify your answer.