Air and Water

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  • Air and Water
    • Gases in the atmosphere
      • 200million years ago
        • proportions of gases in Earth's atmosphere had stabilised
          • much the same as they are today
          • Nitrogen 78%
          • Oxygen 21%
          • Argon 0.9%
          • Carbon Dioxide 0.04%
          • also small % of pollutant gases e.g. Carbon Monoxide, Sulfur Dioxide and oxides of Nitrogen
            • as well as varying amounts of water vapour
    • Separating gases in the air
      • In industry - fractional distillation
        • process in which liquids with different boiling points are separated
        • firstly, have to get air cold enough to condense into liquid
          • cooled to below -200°C
        • two stage process
          • 1. compress air to about 150 times atmospheric pressure
            • actually warms it up, so cooled down to normal temp
              • by passing over air pipes  carrying cold water
          • 2. provides main cooling, takes place when pressure is released
            • air allowed to expand rapidly, similar to aerosol cans
              • temp drops far enough for even gases in air to condense to liquids
                • CO? and water can be removed easily from mixture before frac. dist. takes place
                  • these two are solids at room temp.
        • Boiling points of main substances
          • Nitrogen: -196°C
          • Argon: -186°C
          • Oxygen: -183°C
        • Column colder at top than bottom so at -196°C nitrogen boils 1st
          • -185°C oxygen still cold enough to be liquid as it boils at -183C
            • so O? can be separated off as a liquid from bottom of column
          • small amount of argon can be collected from column
            • Untitled
      • Uses of 3 main gases
        • Liquid Nitrogen
          • cool things down at very low temp.
            • at these temps most things solidify
            • used to store sperm in hospitals to help in fertility treatment
        • Nitrogen Gas
          • very unreactive
            • sealed food packaging to stop decay
            • oil tankers
              • when oil pumped ashore to reduce risk of explosion
            • ammonia
              • convert into fertilisers
        • Oxygen
          • help people breathe, often at scene of accident or hospital
          • help things react
            • high temp welding and steel making process
    • Oxygen and Oxides
      • reactive gas in air is oxygen
        • when any substance burns, it reacts with oxygen gas in air to form compounds
          • i.e. oxides
        • elements burn more vigorously in pure oxy than air as only 21% oxy
        • metallic elements burn to form solid oxides
          • 2Mg + O? ? 2MgO
          • 4Li + O?  ? 2Li?O
          • known as combustion reactions
            • non-metallic elements burn often form oxides which are produced as gases
              • C + O? ? CO?
              • S + O? ? SO?
            • OXIDATION
            • opposite is reduction - important for extraction of metals from ores
        • non-metallic elements burn often form oxides which are produced as gases
          • C + O? ? CO?
          • S + O? ? SO?
      • Metal Oxides
        • if dissolved in water, makes an alkaline solution
        • however some do not dissolve in water
          • e.g. copper oxide
            • test neutral with UI
              • however does react with acid
          • also known as a BASE
        • amphoteric oxides
          • react like both acids and bases
            • do not dissolve in water
              • cannot test pH of solutions formed
      • Non-metal Oxides
        • most dissolve in water to form acids
      • In general, Metal oxides are basic, Non-metal oxides are acidic
    • Water Treatment
      • Water from natural resources contains dissolved minerals and microbes
        • have to be reduced to meet safety standards
        • best sources contain low levels of minerals and microbes to start with
        • when taken from rivers and reservoirs needs to be treated to be safe to drink
          • treatment involves...
            • passing untreated water through filter beds made of sand to remove solid particles
            • addition of chlorine to sterilise water by killing microbes
          • people often have filter jugs at home
            • usually have top part into which you put tap water
              • as water goes from top to bottom, passes through a filter cartridge
                • often contains activated carbon, an ion-exchange resin and silver
                  • carbon reduces levels of chlorine, pesticides and other organic impurities
                  • ion-exchange removes calcium, magnesium, lead, copper and aluminium ions
                  • silver nano particles discourage growth of bacteria within filter
                • cartridge should be changed every few weeks
      • Pure water
        • water can be made pure by distillation
          • boiling followed by condensation of steam
          • however expensive process due to energy costs involved in heating large vols of water
        • in countries with few sources of freshwater, seawater is made usable
          • process known as desalination
            • seawater undergoes distillation at industrial plant
              • but at reduced pressure to lower b.p. and save energy
            • however still caro
      • Fluoride in water
        • Arguments for
          • some areas have had fluoridated water for about 50 years - no one has seen harmful effects
          • 30% reduction of cavities in teeth
          • need fluoridation to protect teeth of those who don't have good dental hygiene habits and don't visit dentists regularly
          • bacteria associated with tooth decay will also cause some types heart disease
          • fluoride is only added in tiny amounts anyway
        • Arguments against
          • Fluorosis is a condition caused when children take too much fluoride
            • white streaks/tips appear on teeth - deposits of calcium fluoride
              • these are porous and can become stained
          • benefit of fluoridation is not significant, so why should we risk our health?
          • ethically wrong to give people treatments they have not consented to
          • some excess fluoride can affect the brain, producing learning difficulties and Alzheimer's
    • Rusting
      • both air (oxygen) and water are needed for iron to rust
      • providing a barrier between iron and air and water protects iron from rusting
        • paint, oil/grease, plastic, a less/more reactive metal
      • sacrificial protection provides protection against rusting even when the iron is exposed to air and water. The iron needs to be attached to a more reactive metal
        • i.e. zinc, aluminium or magnesium
          • galvanisation
      • rust = hydrated iron oxide
  • 200million years ago
    • proportions of gases in Earth's atmosphere had stabilised
      • much the same as they are today
      • Nitrogen 78%
      • Oxygen 21%
      • Argon 0.9%
      • Carbon Dioxide 0.04%
      • also small % of pollutant gases e.g. Carbon Monoxide, Sulfur Dioxide and oxides of Nitrogen
        • as well as varying amounts of water vapour

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