Acidic_Environment

1. The main industrial origin of sulphur dioxide is the burning of fossil fuels, particularly coal and petroleum. Particularly in the burning of coal, the problem arises due to these fuels containing some compounds of sulphur as impurities. When these fuels are burnt, the sulphur is oxidised to produce sulphur dioxide: 4DeS29s0 + 11O2(g) -> 2Fe2O3(s) + 8SO2(g) SO2 is the major contributor to acid rain that can affect places thousands of kilometres from the source. Sulfur can be removed from coal during the burning process by using limestone and can also be removed from fossil fuels prior to burning the fuel. This prevents the formation of SO2. It can also come from the smelting of sulphide ores. For example, the smelting plant releasing Sulfur dioxide into the atmosphere is the roasting of chalcopyrite in the extraction of copper: 2CuFeS2(s) + 5O2(g) + 2SiO2(s) -> 2Cu(l) + 4SO2(g) + 2FeSiO3(l) b) Nitrogen oxides greatly contribute to the acidic oxide pollutants in the atmosphere mainly de to the internal combustion of engines. Nitrogen oxides are formed in car engines and other high-temperature combustion environments because the high temperatures cause nitrogen and oxygen in the air to react: N2(g) + O2(g) -> 2NO(g) 2NO(g) + O2(g) -> 2NO2(g) Nitrogen oxides contribute to the formation of photochemical smog and acid rain. C) The release of gases such as sulphur dioxide and nitrogen oxides in the environment arouses many reasons for concerns. Sulfur dioxides come naturally from volcanoes, bushfires and the decomposition of organic material. They come industrially from the burning of coal and the smelting of lead and copper. Sulfur dioxide and trioxide are highly irritating gases which present major health risk, especially for people suffering from asthma and other respiratory disorders. For example, the London smogs in the 1950’s resulted in many deaths. When sulfur dioxides enter the atmosphere they may dissolve to produce acid rain. Acid rain then causes much damage to buildings and statues and is responsible for the destruction of forests, crops and aquatic life in lakes (making it too acidic for some animals to live and may also disrupt the reproductive life of animals). Nitrogen oxides come naturally from lightning and industrially from the internal combustion in engines and the high temperature furnaces. They are important components in the formation of photochemical smog. They also contribute to the formation of acid rain. 2. A) Acid rain is caused by emissions which react with the water molecules in the atmosphere to produce acids. It is the result of rain dissolving sulphur oxides(SO2 and SO3) and nitrogen dioxide (NO2). The rain then forms a dilute solution of different acid. This includes sulfurous, sulphuric and nitric acids. These emissions in the atmosphere are usually the result of burning fossil fuels or high-temperature combustion processes as those such in motor vehicles. In the Gas phase, the sulphur dioxide produced is oxidised in the air to form sulphur trioxide: 2SO2(g) + 02(g) -> 2SO3(g) Nitrogen oxide emissions bring about the reaction of atmospheric nitrogen and oxygen: N2(g) + 02(g) + heat -> 2N0(g) The Nitric oxide produced is oxidised to form nitrogen dioxide: 2NO(g) + 02(g) ->2NO2(g) When dissolved in water, these sulphur and nitrogen oxides produce acids: * SO2(g) + H2O(l) -> H2SO4(aq) - sulphurous acid * SO3(g) + H2O(l) -> H2SO4(aq) - Sulfuric acid * 4NO2(g) + 2H2O(l) + 02(g) ->4HNO3(aq) - Nitric Acid These acids are then referred to as ‘acid rain’. B) Acid rain can cause surface waters to become acidic and therefore have a large impact on the aquatic ecology and can greatly affect the reproduction of fish, frogs and other aquatic life. It can also affect forests, crops and plant life directly by damaging plant foliage. It also effects the soil as changes in pH can slow the growth of plants and in some cases, even stop growth all together. Acid rain can also damage infrastructure due to the damage to metal and stone buildings and infrastructure. This reaction is: CaCO3(s) + 2H+(aq) -> Ca2+(aq) + CO2(g) + H20(l) Acid rain also has impacts on human health, not by direct touch, but through the gases that are inhaled deep into people’s lungs. It can cause heart and lung disorders, such as asthma and bronchitis. There is current research in ways to reduce the emissions for sulphur and nitrogen oxides. These include, removing sulphur oxides from atmospheric emissions using a scrubber, or the use of catalytic converters in motor vehicles to reduce nitric oxide. 3. Acids as food additives: Food acids (flavours and preservatives) are used to help maintain a constant level of acidity and to produce a sharp or sour flavour. * Acetic Acid (260) CH3C00H: Antibacterial. Originates from methanol from gas or oil, and carbon monoxide to manufacture acetic acid. CH3OH+CO-->CH3COOH * Substance permitted to stabilise the acidity of food. * Diluents for colouring matter * Flavouring agent * The acetic acid in vinegar is formed by the action of the bacterium Acetobacter on the alcohol in beer for malt vinegar, or cider or wine, for those vinegars. Give vinegar it’s sour taste. * Used in: pickles, chutneys, cheese, salad cream, mint sauce and jelly etc. Tartaric Acid (334): Widely occurring fruit acid. Found in grapes and other fruits either free or combined with K, Ca or Mg. * Antioxidant; capable of increasing the antioxidant effect of other substances (synergist). * To adjust acidity in frozen/dariy products, jellies, bakery, beverages, confectionary, sweets and wines * Diluents for food colours * Constituent of grape and other artificial flavours * Acid in some baking powders Malic Acid (296): Malic acid occurs in nature (e.g. green apples, pears and potatoes) and is an important metabolite in all living cells. Commercial malic acid is usually a mixture of D-form and L-from and is made by a chemical synthesis by heating malic with dilute sulphuric acid under pressure. * Acid, flavouring Used in fruit butters, sweetened coconut, packet spaghetti sauce mix, low caloric orange soft drink etc. 4. Naturally occurring acids: -Carbonic Acid- H2CO3: is found in the blood and is a step in in the process of transportation of CO2 out of the body via respiratory gas exchange. - Stomach acid-HCl(aq): naturally occurring in the stomach in the digestion of food. -Acid Rain- H2SO4 and HNO3 are formed from Nitrogen and Sulfur reacting with H2O in the atmosphere. Naturally occurring bases: -Putrescine- H2N(CH2)3NH2: found in seawater/seafood - Sodium Carbonate-Na2CO3: commonly occurs as a crystalline heptahydrate, which readily effloresces to form a white powder, monohydrate. - Ammonia-NH3: a colourless gas compound of nitrogen and hydrogen found in trace quantities in the atmosphere and produced from the decaying process or nitrogenous animal and plant matter. 5. Neutralisation Reactions: A neutralisation reaction is when you mix an acid and a base together. The general equation: Acid + Base = Metallic Salt + Water e.g. HCl + NaOH -> H2O(l) + NaCl The basis of all neutralisation reactions is the reaction between hydrogen ions and hydroxide ions to form water. This is a proton transfer reaction. To neutralise spills of concentrated acid on floors and benches you can add the weak base sodium carbonate then wash with a large volume of water. Being a weak base, it will not produce much heat when it neutralises then acid. A weak acid such as acetic acid can be used to safely neutralise spills of bases on floors and benches. As the hydrogen carbonate ion can react with bases as well as acids, it can also be safely used to neutralise a spill of a concentrated base. Bibliography: Websites: http://hsc.csu.edu.au/chemistry/core/acidic/chem932/chem932net.html 30.1.11 http://en.wikipedia.org/wiki/Sulfur_dioxide 28.1.11 http://www.angelfire.com/droid/hsc/acid.htm 28.1.11 http://en.wikipedia.org/wiki/Acetic_acid 2.2.11 http://en.wikipedia.org/wiki/Sodium_carbonate 21.2.11 http://wiki.answers.com/Q/What_is_a_neutralization_reaction 21.2.11 http://sydney.edu.au/science/uniserve_science/school/curric/stage6/chem/acidenv.html 21.2.11 http://www.hsc.csu.edu.au/chemistry/core/acidic/chem934/chem934net.html#net21 21.2.11 http://www.epa.gov/acidrain/effects/health.html 2.2.11 Books: 1. The New Additive Code Breaker, Thomas G. Lothian, 1989, Maurace Hanson, Melbourne VIC, 10.2.11 2. The Acidic Environment Surfing Chemistry, Science Press 2006, NSW Australia, 22.2.11 3. Chemistry Contexts 2, Debbie Irwin, Pearson Education Australia, Melbourne Australia, 22.2.11