Atmosphere 2

• The Earth is wrapped in a layer of gases called the atmosphere
• Layers of the atmosphere

  • Troposphere
  • Stratosphere
  • Mesosphere
  • Thermosphere
• The balance in the atmosphere is continuously influenced by human activity
• Air pollution has been increasing ever since the birth of the Industrial Revolution
• Hydrogen is not found naturally in air but in makes up about 10% of living organisms
• An atom of hydrogen's most abundant isotope has no neutrons
• Hydrogen is believed to be one of the three elements produced in the Big Bang (theory)
• Hydrogen is the most abundant element in the Universe
• Oxygen is much more soluble in water than nitrogen and there is present in higher concentrations in water allowing aquatic organisms to live
• Almost half of the mass of the Earth's crust comes from oxygen
• Nitrogen is the most abundant gas in air
• Oxygen is the third most abundant gas in the universe but the second most abundant gas in air
• Approximately 65% of an adult's body is made up of water
• Water is essential for living organisms
• Water expands as it cools from 4oC to 0oC
• Water covers 70% of the Earth's surface
• Mixture


  A combination of two or more substances that are not chemically combined
• Separation of air by fractional distillation of liquid air


  1. Air is initially filtered to remove any dust particles

  2. Air is cooled to -200oC

  3. Carbon dioxide freezes at -79oC and is removed

  4. Nitrogen and oxygen turn into liquids

  5. Nitrogen and oxygen are separated by fractional distillation based on their different boiling points
• Measuring the percentage of oxygen in air


  1. An excess of copper turnings is placed in a hard glass tube connected to two gas syringes

  2. 100cm3 of air is passed over the heated copper turnings

  3. The syringes are left to cool to room temperature before taking readings

  4. The volume of oxygen used is measured

  
• 100cm3 of air contains 21cm3 of oxygen, so the percentage of oxygen gas in air is 21%
• Nitrogen


  • Neutral gas
  • Colourless and odourless
  • Slightly soluble in water
  • Very unreactive compared to oxygen
  • Reacts with hydrogen to form ammonia
  • Reacts with oxygen at high temperatures to form oxides
• Uses of nitrogen


  • Liquid nitrogen for quick-freezing food, storing cells, etc.
  • Flushing food packaging to remove oxygen
  • Producing ammonia
• Oxygen


  • Colourless, odourless and neutral gas
  • Slightly soluble in water
  • Slightly denser than air
  • Exceptionally reactive, combining with many metals and non-metals

  
• Uses of oxygen


  • As an aid to breathing
  • In oxyacetylene torches
  • For making steel
  • In sewage treatment
• Carbon dioxide


  • Colourless and odourless gas
  • Denser than air
  • Does not support combustion
  • Slightly soluble in water, forming carbonic acid
  • Not poisonous but does not support respiration
• Uses of carbon dioxide

  • Taken up by plants in photosynthesis
  • Production of sparkling drinks
  • Fire extinguishers
  • Coolant
• Noble gases


  • Colourless gases
  • Monoatomic
  • Very unreactive
  • Become denser as you go down the group
  • Boiling points increase as you go down the group
• Uses of noble gases

  • Helium in weather balloons and diving tanks
  • Argon in light bulbs
  • Neon in advertising signs and lasers
  • Krypton and xenon in lighthouse lamps and lasers
• The remaining percentage of air from the copper-gas syringes experiment is mainly nitrogen
• Testing for carbon dioxide

  Bubbling the gas in limewater, which turns milky due to the formation of calcium carbonate

  
• Desiccant


  A chemical that absorbs water vapour but does not change its state
• Deliquescent


  A chemical that absorbs water vapour and changes its state by forming a concentrated solution
• The presence of water vapour can be detected using silica gel crystals containing cobalt(II) chloride or blue cobalt(II) chloride paper, which change colour in the presence of water

  
• Oxygen


  • Chemical formula O2
  • Very low boiling point of -183oC
  • Slightly soluble in water
  • Slightly denser than air
• Laboratory preparation of oxygen

  Catalytic decomposition of hydrogen peroxide using manganese(IV) oxide as a catalyst
• Hydrogen peroxide decomposes to form water and oxygen gas in the presence of manganese(IV) oxide
• Approximately 1% of the air (less than 1%) are noble gases which are very unreactive because they have a full outer shell of electrons
• Oxygen


  • A very reactive gas that supports combustion, with chemical formula O2 (a diatomic element)
  • Has a very low boiling point (-183°C)
  • Is only slightly soluble in water
  • Is slightly denser than air

  
• Laboratory preparation of oxygen

  1. Catalytic decomposition of hydrogen peroxide (H2O2)

  2. Hydrogen peroxide solution is added to manganese(IV) oxide (MnO2) which catalyses the decomposition

  3. Effervescence (bubbles) is observed

  4. Oxygen is collected over water

  
• Hydrogen peroxide solution decomposes very slowly on its own, but the reaction is faster in the presence of light