Gases of the Atmosphere

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Gases of the Atmosphere

• Chapter 20

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Nitrogen - Properties

• A colourless and odourless gas
• Insoluble in water
• Generally unreactive. Its low reactivity can be
  related to the strong triple bond between the two
  nitrogen atoms in each N2 molecule.

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Nitrogen - Uses

• Plants need a continual supply of nitrogen
  because it are a key component of cells of all
  living things. (Can not use nitrogen gas
  directly).
• Nitrogen-based fertilisers are compounds of
  nitrogen added to soils to complement bacterial
  nitrogen fixation and so maximise crops.
• The low reactivity of nitrogen makes it useful
  when an unreactive oxygen-free environment is
  required. Such as removing flammable vapours from
  oil pipelines and tanks.
• The low boiling temperature of liquid nitrogen
  (-196C) makes it suitable for storage of frozen
  eggs, sperm and embryos.

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Commercial Production of Nitrogen

• Nitrogen is produced by fractional distillation
  of liquid air. As liquid air at the bottom of the
  distillation column evaporates, nitrogen, which
  has a lower boiling temperature than the other
  gases in the air, rises the most in the column
  and can be collected.

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Commercial Production of Nitrogen
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Oxides of Nitrogen

• Nitrogen forms a number of compounds with oxygen.
  
• Nitrogen(II) oxide (NO) forms whenever nitrogen
  and oxygen are mixed at extremely high
  temperatures.
• High temperature can be generated in the
  atmosphere by lightning flashes and meteor tails.
• They are also reached in volcanoes and combustion
  engines.

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NO and NO2

• Nitrogen (II) oxide is formed by
• This colourless gas is difficult to isolate
  because it reacts readily with oxygen, at lower
  temperatures, to form the brown poisonous gas
  nitrogen(IV) oxide (NO2 )

energy
N2(g) O2(g)
2NO(g)
2NO(g) O2(g)
2NO2(g)
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Laboratory Preparation of NO

• 3Cu(s) 8HNO3(aq) ? 3Cu(NO3)2(aq) 4H2O(l)
  2NO(g)

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Lab Preparation of NO2

• Cu(s) 4HNO(aq) ? Cu(NO3)2(aq) 2H2O(l)
  2NO2(g)
• This preparation uses concentrated nitric acid
  instead of 50 nitric acid. See figure 20.6 in
  your text to see how it is collected.

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Your Turn

• Page 348
• Question 2

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Oxygen

• Oxygen is the most abundant element in the
  Earths crust and comprises 21 by volume of the
  atmosphere.
• Oxygen is vital for life on this planet.
• Without a constant and adequate supply of oxygen,
  most living things could not exist. Why?
• The energy released by reactions of oxygen with
  fossil fuels is the source of most of the heat
  and electrical energy needed to run our world.

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Properties of Oxygen

• Is a colourless and odourless gas.
• Is slightly soluble in water. One litre will
  dissolve 0.03L of oxygen at 20C and 1 atm.
  Although the solubility of oxygen is low, enough
  of it will dissolve in water to support aquatic
  life.
• Supports combustion
• Reacts with most metals to form basic oxides
  (basic oxides react with acids).
• Reacts with most non-metals to form acidic oxides
  (these dissolve in water to form acids).

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Uses of Oxygen

• Manufacture of steel. Oxygen is used to oxidise
  some impurities and reduce their amount in steel.
• Manufacture of chemicals. Some chemicals that are
  produced in large amounts such as sulfuric acid
  and methanol, also require large quantities of
  oxygen.
• Medical uses. To help patients with respiratory
  problems. Oxygen enriched air is given to people
  who have been exposed to toxic fumes.
• Sewage Treatment, helps to oxidise organic
  matter.
• Combustion processes.

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Laboratory Preparation of Oxygen
MnO2
2H2O2(aq)
2H2O(l) O2(g)
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Your Turn

• Page 352
• Questions 3 and 4

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Carbon Dioxide

• Only 0.035 is present in the total volume of the
  atmosphere, yet this concentration is sufficient
  to sustain life on Earth.
• How does it sustain life on Earth??
• What is the equation for this process??

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Properties of Carbon Dioxide

• Is a colourless, odourless gas.
• Will not support combustion unless the fire is
  hot enough to break the CO bond.
• (Magnesium is one of the few substances that can
  burn in carbon dioxide).
• Is denser than air.
• At atmospheric pressure does not form a liquid.
• Is slightly soluble in water 1.5g will dissolve
  in 1 litre of water.
• Forms slightly acid solutions, for example
  carbonic acid (H2CO3)

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Preparation of Carbon Dioxide

• Commercially Carbon dioxide can be obtained as a
  by-product of the fermentation of sugars to
  alcohol
• C6H12O6(aq) ? 2C2H5OH(aq) 2CO2(g)
• In a laboratory it is prepared by the reaction of
  dilute HCl with calcium carbonate in the form of
  marble chips. The gas is collected over water.
• CaCO3(s) 2HCl(aq) ? CaCl2(aq) CO2(g) H2O(l)

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Uses of Carbon Dioxide

• Photosynthesis.
• To make carbonated drinks. Carbon dioxide is
  dissolved in the drink at high pressure. It comes
  out of solution as bubbles when the can is
  opened.
• Dry ice is used as a refrigerant.
• Fire extinguishers. Carbon dioxide is denser than
  air, so it can blanket fires and reduce the
  access of oxygen to the fuel.

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Your Turn

• Page 354
• Questions 5 and 6