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Properties of air

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					Properties of air
   colourless (無色)
   odourless (無味)
   mixture of different gases:
       nitrogen       (氮)          78 %
        oxygen        (氧)          21 %

    carbon dioxide   (二氧化碳)       0.03 %
      noble gases    (惰性氣體)        0.9 %
     water vapour    (水蒸氣)        variable
     Tests for gases
                          O2              CO2          N2
     colour         colourless      colourless      colourless

      smell             no smell        no smell     no smell

  burning splint   relight (重燃)         goes out     goes out

 glowing splint     relight             goes out     goes out
hydrogencarbonate
                  red      purple red      yellow remain red
    indicator
   lime water       colourless          milky       colourless
Nitrogen (N2)
   Percentage in air:
        78 % (about 4/5 of the air)

   Characteristics:
        colourless
        odourless
        very un-reactive(stable) (穩定)
        most in the air
Nitrogen (cont’d)
    Uses:
    1.   used in electronic industry    make electronic parts
    2.   cooling effect (-196 °C)    fast freezing (急凍)
    3.   fertilizers (肥料)
    4.   fireworks (煙花)
    5.   anaesthetic (麻醉藥)

    Test(s):
         no simple test
Oxygen (O2)
   Percentage in air:
        21 %

   Characteristics:
        colourless
        odourless
        support burning (助燃)
Oxygen (cont’d)
    Uses:
    1.   need for all living things to keep alive (生存)
    2.   medical use baby in oxygen box
    3.   burning      BBQ
    4.   diving (潛水) : the breathing (呼吸) of diver
    5.   welding (燒焊)

    Test(s):
         a glowing (半熄滅的) splint (木條) : relight
Carbon Dioxide (CO2)
   Percentage in air:
        0.03 %

   Characteristics:
        colourless
        odourless
Carbon Dioxide (cont’d)
    Uses:
    1.   need for plant photosynthesis (光合作用)
    2.   making soft drinks (汽水)
    3.   fire extinguishers (滅火器)
    4.   dry ice (乾冰)

    Test(s):
         hydrogencarbonate indicator : red to yellow
         lime water : colourless to milky
Noble gases(inert gases)
   Examples:
        helium, neon, xenon, argon

   Percentage in air:
        0.9 %

   Characteristics:
        colourless
        odourless
        chemically stable
Noble gases (cont’d)
    Uses:
    1.   fill in light bulb   prevent overheat (過熱) of
         filament
    2.   used in advertising signs (廣告牌) glow in
         different colour when electric current passed
    3.   helium replace hydrogen fill in airships or
         balloons
    4.   diving : mixture of helium & oxygen
Water vapour
    Percentage in air:
         variable

    Characteristics:
         colourless
         odourless
         condense to water droplets (水滴) on a cold surface

    Test(s):
         dry cobalt chloride paper : blue to pink
    Can’t use our hands to touch the paper !!!
     Relative humidity
       humidity : amount of water vapour in the air
       relative humidity :

             amount of water vapour in the air


max. amount of water vapour in the air at the same temp.
    Breathed & unbreathed air

                              Breathed air       Unbreathed air

   burning splint       goes out quickly      goes out slowly
hydrogencarbonate
                        red        yellow remain unchange(red)
    indicator

cobalt chloride paper   blue           pink    remain unchange
   Summary of activities

aim :
    carry out simple tests to show the composition of air
conclusion :

    oxygen relights a glowing splint & burns more intensely for
    a burning splint
    carbon dioxide turns hydrogencarbonate indicator from red
    to yellow & turns lime water from colourless to milky
    no simple test for nitrogen
   Summary of activities (cont’d)

aim :
    to prove the existence (存在) of oxygen in the air
conclusion :

    there is oxygen in the air

    air is not totally made up of oxygen
   Summary of activities (cont’d)

aim :
    find out the percentage of oxygen in the air
conclusion :
          rise in water level
                                100 % = ~ 21 %
        length of boiling tube
    air contains about 21 % of oxygen
   Summary of activities (cont’d)

aim :
    to prove the existence of carbon dioxide in the air
conclusion :

    air contains a small amount of carbon dioxide
   Summary of activities (cont’d)

aim :
    to prove the existence of water vapour in the air
conclusion :

    air contains a small amount of water vapour
   Summary of activities (cont’d)

aim :
    find out the difference between breathed & unbreathed air
conclusion :

    characteristics of breathed air :
         1.    less oxygen
         2.    more carbon dioxide
         3.    more water vapour
         4.    warmer
Hydrogencarbonate indicator

      % of carbon dioxide      colour of indicator

 > 0.03 (e.g. breathed air)     yellow
about 0.03 (e.g. atmosphere)        red
           < 0.03               purple
 Hydrogen v.s. Helium

          Hydrogen                         Helium

       light in mass                  light in mass
danger (may lead explosion)     safe (chemically stable)
  not recommended to use      use : to fill airship or balloons

				
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posted:10/8/2012
language:English
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