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

Properties of air colourless colourless ( 無色 ) odourlessodourless ( 無味 ) mixture of different gases:

nitrogennitrogen (( 氮氮 )) 78 %78 %

oxygenoxygen (( 氧氧 )) 21 %21 %

carbon dioxidecarbon dioxide (( 二氧化碳二氧化碳 )) 0.03 %0.03 %

noble gasesnoble gases (( 惰性氣體惰性氣體 )) 0.9 %0.9 %

water vapourwater vapour (( 水蒸氣水蒸氣 )) variablevariable

Tests for gases

OO22 COCO22 NN22

colourcolour colourless colourless colourless

smellsmell no smell no smell no smell

burning splintburning splint relight ( 重燃 ) goes out goes out

glowing splintglowing splint relightrelight goes out goes out

hydrogencarbonate hydrogencarbonate

indicatorindicatorred purplered purple red yellowred yellow remain red

lime waterlime water colourless milkymilky colourless

Nitrogen (N2)

Percentage in air:78 %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 %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 ) : relightrelight

Carbon Dioxide (CO2)

Percentage in air:0.03 %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 : redred to yellowyellowlime water : colourlesscolourless to milkymilky

Noble gases(inert gases) Examples:

helium, neon, xenon, argon

Percentage in air:0.9 %0.9 %

Characteristics:colourlessodourless 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:

variablevariable

Characteristics:colourlessodourlesscondense to water droplets ( 水滴 ) on a cold surface

Test(s):dry cobalt chloride paper : blueblue to pinkpink

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 airamount of water vapour in the air

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

Breathed & unbreathed air

Breathed airBreathed air Unbreathed airUnbreathed air

burning splintburning splint goes out quicklyquickly goes out slowlyslowly

hydrogencarbonate hydrogencarbonate

indicatorindicatorred red yellowyellow remain unchange(red)

cobalt chloride papercobalt chloride paper blueblue pink pink remain unchange

Summary of activities

aim :aim :

conclusion : conclusion :

carry out simple tests to show the composition of aircomposition of air

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 :aim :

conclusion : conclusion :

to prove the existenceexistence ( 存在 ) of oxygenof oxygen in the air

there is oxygen in the air

air is not totally made up of oxygen

Summary of activities (cont’d)

aim :aim :

conclusion : conclusion :

find out the percentage of oxygenpercentage of oxygen in the air

rise in water level

length of boiling tube 100 % = ~ 21 %

air contains about 21 % of oxygen

Summary of activities (cont’d)

aim :aim :

conclusion : conclusion :

to prove the existenceexistence of carbon dioxideof carbon dioxide in the air

air contains a small amount of carbon dioxide

Summary of activities (cont’d)

aim :aim :

conclusion : conclusion :

to prove the existenceexistence of water vapourof water vapour in the air

air contains a small amount of water vapour

Summary of activities (cont’d)

aim :aim :

conclusion : conclusion :

find out the differencedifference between breathed & unbreathed air

characteristics of breathed air :

1. less oxygen

2. more carbon dioxide

3. more water vapour

4. warmer

Hydrogencarbonate indicator

%% of carbon dioxide of carbon dioxide colour of indicatorcolour of indicator> 0.03 (e.g. breathed air) yellowyellow

about 0.03 (e.g. atmosphere) redred

< 0.03 purplepurple

Hydrogen v.s. Helium

HydrogenHydrogen HeliumHelium

lightlight in mass lightlight in mass

dangerdanger (may lead explosion) safesafe (chemically stable)

notnot recommended to use useuse : to fill airship or balloons