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YEAR 11 DP CHEMISTRY. Non-metal Oxides Sources 1. Atmospheric O2 1. Atmospheric O2 is very reactive and reacts with many substances to form oxides 2.

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Presentation on theme: "YEAR 11 DP CHEMISTRY. Non-metal Oxides Sources 1. Atmospheric O2 1. Atmospheric O2 is very reactive and reacts with many substances to form oxides 2."— Presentation transcript:

1 YEAR 11 DP CHEMISTRY

2 Non-metal Oxides Sources 1. Atmospheric O2 1. Atmospheric O2 is very reactive and reacts with many substances to form oxides 2. Natural formation 1. CO2 – from respiration (“burning” sugars for energy) 2. NO2 – from lightning strikes (N2 + 2O2 in the air  2NO2) 3. SO2 – released from volcanoes or H2S + O2  SO2 + H2O (H2S produced by bacterial decomposition of organic matter) 3. Human causes 3. Human causes (bushfires and burning fossil fuels) 1. CO2 – fossil fuel combustion product 2. NO – high temperature combustion product 3. NO2 – NO is easily oxidised in the air (NO + O2  NO2) 4. SO2 – burning coal that contains S as an impurity 5. SO3 – SO2 is easily oxidised in the air

3 Acidic Non-metal Oxides Many non-metal oxides react with water in the atmosphere to produce acids; CO2 + H2O  H2CO3 (carbonic acid) SO2 + H2O  H2SO3 (sulfurous acid) SO3 + H2O  H2SO4 (sulfuric acid) 2NO2 + H2O  HNO3 + HNO2 (nitric and nitrous acid) These non-metal oxides are all gases Their acidic products all contribute to the acidity of rain

4 Oxide Trends in the Periodic Table Oxides tend to increase in acidity from left to right In general: Metal oxides are basic (left side) Non-metal oxides are acidic (right side) Exceptions: Amphoteric oxides (i.e. Al, Be, Ga, Sn, Pb) Why this trend? This is due to electronegativity increasing from left to right (see following slides for more details)

5 Oxides on the left side of the PT (basic) Electrons are transferred to the O 2- This is due to the ionic nature of these bonds because of a large difference in electronegativities, therefore ions are formed in solution For example For example:elementelectronegativity Na0.93 O3.44 This means This means: Na2O (aq)  Na + + O 2- and O 2- + H +  OH - (readily) This overall consumption of H + ions leads to an increase of pH (i.e. Basic)

6 Oxides on the right side of the PT (acidic) Electrons are shared with the O 2- This is due to the covalent nature of these bonds because of a small difference in electronegativities, thus no ions are formed For example For example:elementelectronegativity S2.58 O3.44 This means This means: Due to a partially positive S central atom, SO3 (aq) + H2O  H + + HSO4 - This overall production of H + ions leads to an decrease of pH (i.e. acidic). (See following slide for details of this reaction)

7 Sulfur trioxide forms an acid O S O O H+H+ OH - - H+H+ water Sulfuric acid solution Sulfur trioxide O S OH O O


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