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FOCUS 5.8 PROPERTIES AND USES OF AIR

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									FOCUS 5.8 PROPERTIES
AND USES OF AIR
THE COMPOSITION OF AIR
 The   air is a mixture of gases, as follows:

 78%  Nitrogen
 21% Oxygen

 0.03% Carbon dioxide

 0.97 % Other gases (noble gases, water
  vapour, methane gas, nitrous oxide,
  carbon monoxide)
CHEMICAL PROPERTIES OF
          AIR

              OXYGEN

 Theoxygen in the air reacts with
 other substances in a process called
 oxidation.

 Thepollutants in the atmosphere
 may cause harm to people or the
 environment.
WHEN MAGNESIUM BURNS IN
           AIR
   IT USES UP OXYGEN
RUSTING IS A CHEMICAL PROCESS THAT
  OCCURS WHEN WET IRON COMES IN
      CONTACT WITH OXYGEN
 RUSTING CAN BE PREVENTED BY
THE INTRODUCTION OF A BARRIER
           BETWEEN
IRON AND THE OXYGEN IN THE AIR
  CARBON DIOXIDE

The carbon dioxide is used by
 plants to make sugar by the
 process of photosynthesis.

Itprovides food and replaces
 the oxygen gas in the air.
 POLLUTANTS IN OUR ATMOSPHERE
INCLUDE GASES AND AEROSOLS AND
 CAN IRRITATE YOUR RESPIRATORY
            SYSTEM.
 THE INCREASE IN CARBON DIOXIDE IN THE
ATMOSPHERE COMES FROM MANY SOURCES,
INCLUDING RESPIRATION, FERMENTATION,
   COMBUSTION AND MANY DIFFERENT
        INDUSTRIAL PROCESSES.
PHYSICAL PROPERTIES OF
          AIR
 Airis elastic.
 This property of air is used to drive
  machines known as pneumatic
  devices.
THE ENERGY IN MOVING AIR CAN
     BE USED TO PRODUCE
         ELECTRICITY.
HEATED AIR EXPANDS AND BECOMES
LESS DENSE.
A PROPANE GAS BURNER IS USED TO
HEAT THE AIR IN A HOT AIR BALLOON
CAUSING IT TO RISE. AS THE AIR IN THE
BALLOON COOLS IT WILL BECOME MORE
DENSE AND THE BALLOON WILL FALL.
AIR IS A VERY GOOD INSULATOR
AGAINST HEAT, COLD AND NOISE.
   AIR

1 Air is a mixture and not a compound because the different
  components of air are not chemically combined and can be
  separated using physical methods (air can be separated into
  its components using fractional distillation).
2 a Nitrogen is the most abundant gas in the atmosphere.
• b    Carbon dioxide is the gas used by green plants in the
  process of photosynthesis and the best known greenhouse gas.
• c    Oxygen is the gas used by all living things in the process
  of chemical respiration.
3 Air is only 20 per cent oxygen gas, so a flame will not burn as
  brightly as it would in pure oxygen.
4. A coating of paint or plastic prevents oxygen and moisture
   getting to the surface of the metal, thus reducing corrosion.

5. Three gases that contribute to air pollution are nitrogen
   dioxide, sulfur dioxide and carbon dioxide.

6 ‘Air is a real substance’ means that air takes up space and
  has mass. This can be proved in a number of ways:
• You can find the mass of a basketball before pumping it up
  and comparing it to the mass after pumping it up. The
  increase in mass is due to the air that is now inside it.
• You can try filling a conical flask with water through a
  funnel that is sealed around the neck. The water will not
  enter the conical flask as the air cannot escape.
7. Useful applications—powering an electrical generator,
   windmills, moving a yacht.
   Non-useful applications—storms, hurricanes, tornadoes,
   wind resistance of moving cars.

8 The elastic nature of air refers to the fact that if the air in a
  vessel is compressed, when the force is removed or released
  the air will expand back to its original shape within the
  container. This property is used in tyres and other air-
  operated tools such as a jack hammer.
9. As air is heated it expands and becomes less dense than the
   cooler air that surrounds the balloon. The less dense air of
   the hot-air balloon floats on the cooler air, so it rises. As the
   air in the balloon cools it becomes more dense and falls. The
   height of the balloon can be controlled by using a gas burner
   to heat the air as required.

10 If a jumper is baggy it traps a layer of air between your
   body and the jumper. As air is an insulator it reduces the
   amount of heat that is lost to the environment, keeping you
   warmer.
•   11 If the ball has a split or a hole in it the air escapes from
    the ball when it hits the ground. If the ball is in good
    condition the elastic nature of air means that the ball can
    become distorted when it hits the ground but return the ball
    to its original shape as it leaves the ground. This helps the
    ball bounce back towards its original height (as some energy
    is lost, it will not return to its original height).

•   12 Ozone is considered to be a pollutant when it is produced
    at altitudes closer to the surface. It is a respiratory irritant
    when breathed by humans. At higher altitudes ozone is
    essential in providing protection from UV radiation, which
    can cause sunburn and even cancer in high doses.
•   13 The concept map shows that there are a large number of
    sources of carbon dioxide, including industrial processes,
    fermentation, cellular respiration and burning. The carbon
    dioxide produced in these processes is consumed by plants
    in the process of photosynthesis. It is this balance between
    production and use that is essential in maintaining the
    balance between oxygen and carbon dioxide in our
    environment.
•   14 A 100 per cent oxygen environment is potentially very
    dangerous, as any fire will burn much brighter and more
    rapidly because of the high concentration of oxygen. By
    switching to a 60 per cent oxygen mixture, the rate of
    burning is reduced, which means that any fires will not burn
    as brightly or as rapidly and can be controlled more easily.

								
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