Chemistry-The Atmosphere

• 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 into its component gases


  1. Filtering to remove dust particles

  2. Cooling to -200oC to liquefy air

  3. Fractional distillation to separate nitrogen and oxygen
• Nitrogen gas boils off first

  Because it has a lower boiling point (-196oC) than oxygen (-183oC)
• Measuring the percentage of oxygen in air


  1. Place excess copper turnings in glass tube

  2. Pass 100cm3 of air over heated copper

  3. Measure final volume of air remaining

  
• 100cm3 of air contains 21cm3 of oxygen
• The percentage of oxygen gas in air is 21%
• Copper + oxygen -> copper(II) oxide


  2Cu(s) + O2(g) -> 2CuO(s)

  
• Nitrogen


  • Neutral gas
  • Colourless and odourless
  • Slightly soluble in water
  • Very unreactive
• Uses of nitrogen


  • Liquid nitrogen for freezing food and storing cells
  • Removing oxygen from food packaging
  • Producing ammonia
• Oxygen


  • Colourless, odourless and neutral gas
  • Slightly soluble in water
  • Slightly denser than air
  • Exceptionally reactive

  
• Carbon dioxide


  • Colourless and odourless gas
  • Denser than air
  • Does not support combustion
  • Slightly soluble in water, forming carbonic acid
• 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 balloons and diving tanks
  • Argon in light bulbs
  • Neon in advertising signs and lasers
  • Krypton and xenon in lamps and lasers
• The remaining percentage of air from the copper-gas syringes experiment is mainly nitrogen

  
• Testing for carbon dioxide

  Bubble air through limewater, which turns milky
• Desiccant


  A substance that absorbs water vapour without changing state
• Deliquescent


  A substance that absorbs water vapour and changes state to form a concentrated solution
• Cobalt(II) chloride changes colour from blue to pink in the presence of water vapour
• Noble gases make up approximately 1% of air
• Oxygen


  • Very reactive gas
  • Diatomic element
  • Very low boiling point (-183oC)
  • Slightly soluble in water
  • Slightly denser than air

  
• Laboratory preparation of oxygen


  Catalytic decomposition of hydrogen peroxide using 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