CHEMISTRY Diagram Structure Bonding Na2o Sio2
Total Page:16
File Type:pdf, Size:1020Kb
CHEMISTRY Acidic Environment Assignment Part 2 1) Compare the structure and bonding of the following: (a) sodium oxide, (b) silicon dioxide, and (c) sulphur dioxide Diagram Structure Bonding An ionic lattice. Each unit cell exhibits the anti‐ fluorite structure. Ionic bonding The anions (O2‐) are Na2O in the face‐centred cubic array with the cations (Na+) in all the tetrahedral Red – O2‐ holes. Purple – Na+ Double covalent bonds join two SiO2 Covalent network oxygen atoms to each silicon atom. Red – Silicon Black – Oxygen Double covalent bonds join two oxygen atoms to Polar covalent a sulphur atom. SO2 molecule with bent Due to polarity, structure. there is dipole‐ dipole interaction between gaseous SO2 molecules. 2) Write equations for the reaction of the following with water: COMPOUND REACTION WITH WATER Carbon dioxide CO2(g) + H2O(l) H2CO3(aq) Sodium oxide Na2O(aq) + H2O(l) 2NaOH(aq) Calcium oxide CaO(aq) + H2O(l) Ca(OH)2(aq) Sulfur dioxide SO2(g) + H2O(l) H2SO3(aq) Sulfur trioxide SO3(g) + H2O(l) H2SO4(aq) Nitrogen dioxide NO2(g) + H2O(l) HNO2(aq) + HNO3(aq) 3) Beryllium oxide is amphoteric. (a) Explain what is meant by amphoteric, and (b) Study the two equations below*. Balance them, and indicate whether BeO is acting as an acid or base (a) ‘Amphoteric’ is a term used to describe a substance that exhibits both acidic and basic properties. Beryllium oxide is an amphoteric oxide that reacts with strong acids and strong bases. 2+ ‐ (b)*BeO(s) + 2HCl(aq) + 3H2O(l) Be(H2O)4 (aq) + 2Cl (aq) BeO acting as a base 2+ + *BeO(s) + 2NaOH(aq) + H2O(l) Be(OH)4 (aq) + 2Na (aq) BeO acting as an acid 4) Describe the origins of sulfur dioxide that are causing environmental problems The oxidation of hydrogen sulfide (H2S) which is a product of bacterial decomposition 2H2S (g) + 2O2 (g) 2SO2 (g) + 2H2O (g) The burning of fossil fuels which usually contain sulfide minerals like FeS2. These sulfide minerals in coal are oxidised when the fuel is combusted and sulfur dioxide is released. For example, 4FeS2 (s) + 11O2 (g) 2Fe2O3 (s) + 8SO2 (g) Metal smelters that convert metal sulfides into metals yield vast amounts of sulfur dioxide. For example, smelting chalcopyrite (CuFeS2) to obtain copper results in the release of SO2 2CuFeS2 (s) + 5O2 (g) + 2SiO2 (s) 2Cu (l) + 4SO2 (g) + 2FeSiO3 (l) “In Adelaide in 2000, petroleum refinery processing produced 40% of the sulphur dioxide emitted to the atmosphere, with motor vehicles contributing 22% and fuel combustion 15%.” 1 5) Describe the origins of oxides of nitrogen that are causing environmental problems Nitric oxide is formed when nitrogen and oxygen react at high temperatures, for example, during lightning strikes or high temperature combustion reactions in furnaces and internal combustion engines N2 (g) + O2 (g) 2NO (g) Nitric oxide, a colourless gas and neutral oxide, reacts with oxygen to form nitrogen dioxide, a brown gas and an acidic oxide 2NO (g) + O2 (g) 2NO2 (g) “In Adelaide in 2000, an estimated 66% of nitrogen oxides (including NO and NO2) came from motor vehicles, with a further 20% from fuel combustion.” 1 6) (a) Use www.deh.gov.au/soe/2001/atmosphere/atmosphere02‐16.html to describe the change in acidic oxides in the atmosphere using ice cores from Antarctica. Download the relevant graphs and analyse them (b) Describe the importance of data from ice cores (a) Ice core data obtained from Antarctica (refer to graph below) indicates that the atmospheric concentration of carbon dioxide has increased since AD 1000. It can be seen that prior to the 1800s, CO2 (ppm) showed relatively minor fluctuation ranging from approximately 275ppm‐285ppm. This range may represent the normal concentration of CO2 that works in conjunction with other atmospheric constituents such as methane, nitrous oxide and water vapour to contribute to a natural greenhouse effect. During and after the 1800s, the data from the ice core samples show a very steep increase in CO2 (ppm), from approximately 285ppm in 1800 to 330ppm before the year 2000. This dramatic increase is accounted for by the occurrence of the Industrial Revolution in the 1800s. The burning of fossil fuels to provide power released vast amounts of carbon dioxide and other combustion products into the atmosphere. Since the 1800s, technological advances have placed greater demands on industry and transport in particular, in terms of the generation of power by burning coal. Consequently, in the recent years, there has been a rapid increase in the concentration of atmospheric carbon dioxide. Carbon dioxide concentration from ice core and air samples since AD 1000.Source: CSIRO Atmospheric Research. (b) Ice core data can be used to “reconstruct past climate conditions and climate changes through time...an ice core paleoclimate record can be compared to and combined with other paleoclimate records, for example, from ocean sediment cores, tree rings, coral records and spleotherm (stalactites and stalagmites) records to establish the Earth’s climate history. This climate history can then be used to establish the limits of natural climate variability which can be used to constrain climate models and to help us reduce uncertainty in future climate predictions.” (Secrets from Antarctic Ice, Mark Curran) In other words, data from ice cores is important as it allows us to not only unlock the composition of the ancient atmosphere, but also to understand how our past actions have affected the climate. By understanding causal relationships, such as increased global temperature due to an increase in the concentration of atmospheric carbon dioxide, which in turn is largely due to the burning of fossil fuels, we can forecast climate change based on models of the climate constructed using evidence collected from ice core analysis, such as gas composition of trapped air to determine CO2 levels. Strategies can then be imposed to rectify dim prospects if our present actions are predicted to have an adverse impact on the atmosphere. For example, as ice core research has revealed a link between greenhouse gases and climate change in the past, we need to reduce greenhouse gas emissions, in particular, carbon dioxide. 7) Look up http://www.rta.nsw.gov.au/constructionmaintenance/completedprojects/m5east/m5east currentairqualitydata/currentdata.html (a) Identify the gases that are monitored in the M5 tunnel, (b) Explain why these gases are monitored, and (c) What will happen if the gases in the tunnel exceed the ‘safe’ limit? (a) Carbon monoxide and nitrogen dioxide (b) “As a condition of approving the M5 East Freeway project, the Department of Planning placed strict air quality limits on the operation of the tunnel. As a result, air quality is closely monitored and must continually conform within the limits set.” Air quality limits must not be exceeded as accumulation of the monitored gases will have adverse health effects on users of the tunnel. Both carbon monoxide and nitrogen dioxide are toxic to humans. When inhaled, carbon monoxide binds with haemoglobin to form carboxyhaemoglobin. This reduces an individual’s oxygen‐carrying capacity. At low concentrations, this causes mild headaches and fatigue. These symptoms intensify as concentration increases and respiratory complications become evident. At high concentrations, there is the risk of unconsciousness, convulsions, coma and death. Exposure to nitrogen dioxide at low concentrations results in irritation of the eyes, nose, lungs and throat causing coughing, shortness of breath, fatigue and nausea. Existing respiratory complications such as asthma and emphysema are also aggravated. Particularly susceptible to the health effects of the two gases are young children, the elderly and pregnant women. The build‐up of nitrogen dioxide, a red‐brown gas, also contributes to the formation of haze in the tunnel and reduces visibility. (c) Vehicle emission levels are under constant monitoring in the M5 tunnel. If the concentrations of the gases in the tunnel exceed the ‘safe’ limit, tunnel operators ventilate the tunnel, venting gases from the portals (entrances and exits) to reinstate air quality standards. 8) Explain what is being done by governments and industry to reduce the release of oxides of sulphur and nitrogen In order to reduce emissions of oxides of sulphur and nitrogen, the Australian Government has developed a balanced mix of policy responses by targeting industry, households, governments and communities. Australia is also currently developing a climate change forward agenda to cover the next 20‐30 years. A few examples of the strategies undertaken by the government and industry to reduce emissions include: The Greenhouse Gas Abatement Program (GGAP) ‐ assists Australia in meeting its Kyoto Protocol target. The objective is to reduce Australia's net greenhouse gas emissions by supporting activities that are likely to result in substantial emission reductions or substantial sink enhancement $400 million has been allocated to the Program. A commitment to increase the use of clean renewable energy in Australia. For example, legislation that requires the generation of 9,500 gigawatt hours of extra renewable electricity per year by 2010, enough power to meet the residential electricity needs of four million people. This initiative is being achieved by establishing an innovative market in renewable energy certificates and is expected to deliver in excess of $2 billion of investment in renewable energy in Australia; Working to increase the use of alternative fuels such as compressed natural gas (CNG) and liquefied petroleum gas (LPG) and to improve consumer awareness of the fuel efficiency of their motor vehicles. Regulating the energy efficiency of equipment and many appliances used by Australian households and businesses. This reduces the amount of coal being burnt. Advocating that power companies burn low‐sulfur coal rather than high‐sulfur coal – they can also switch to natural gas which produces very little sulfur dioxide on combustion.