Chemistry 6 marker topics

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Fractional Distillation

  • Crude oil is heated to about 350°C.
  • Most of the hydrocarbons evaporate to form vapours.
  • There is a temperature gradient in the fractionating column. It is cool at the top and hot at the bottom.
  • Vapours / gases rise up the fractionating column. 
  • Vapours / gases cool as they rise up the fractionating column. 
  • When some of / a fraction of the hydrocarbons cool to their boiling point they condense 
  • Hydrocarbons that have lower boiling points and are collected near the top of the fractionating column or hydrocarbons with higher boiling points are collected near the bottom of the fractionating column.
  • Some of the hydrocarbons remain as liquids.
  • Liquids flow to the bottom of the fractionating column. 
  • The condensed fraction (or petrol) separates from the vapours / gases and flows out through a pipe. 
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Earth and its early atmosphere

Early Atmosphere

  • The first four gases on Earth were Carbon Dioxide(CO2), Ammonia (NH3), Methane, (CH4) and steam (H2O). As the earth cooled the steam cooled down and turned into water
  • Very simple photosynthetic organisms evolved e.g. algae.  Oxygen is released which forms a ozone layer which allowed more complex life to evolve as it protects from UV rays, therefore more photosynthesis occurs, therefore more oxygen is produced. However, some of the oxygen reacted with metals to form metal oxides e.g. Iron Oxide. Some of the carbon dioxide dissolved into the oceans. Some end up in sedimentary rock.
  • The ammonia reacts with oxygen in the atmosphere Some bacteria takes up ammonia  and releases nitrogen. 
  • Methane also reacts with oxygen to release CO2 & H2O.

Miller-Urey Experiment

  • They put gases that were found in the early atmosphere into a vessel and gave it an electric shock. The electrical spark was to represent lightning.
  • They found 11 amino acids via this method. They are vital to the beginning of life and the building blocks of protein.
  • Whatever was made by those products was called 'primordial soup', which meant whatever was in it made up the bulding blocks of life. A liquid which contains what we need for life.

Gases in the atmosphere

  • For 200 million years, the proportions of different gases in the atmosphere have been much the same as they are today:

    • about four-fifths (78 %) nitrogen,
    • about one-fifth (21%) oxygen,
    • small proportions of various other gases, including carbon dioxide, water vapour and noble gases

photosynthesis 6CO2 + 6H2O --> C6H12O6 + 6O2.                                                                           ammonia reacts with oxygen 4NH3 + 3O2 --> 2N2 + 6H2O. 

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