CLASS 7TH | CHEMISTRY | AIR AND ATMOSPHERE | REVISION NOTES

Living things cannot live without air.
Air is present everywhere on earth surface up to 300 km above it as well as in water in
dissolved state.

Antoine Lavoisier performed experiment to show the air
components:
He used mercury in this experiment to detect the oxygen from air.
The active part of air used by mercury on heating named as “Oxygen” as it reacts to formed
mercury oxide giving rise to red coloured appearance.
And the remaining 4/5th part is named as “Nitrogen”
He concluded that ration of nitrogen and oxygen in air found to be 4:1 by volume along with
little amount of other gases.

Composition of Air :

 Air is mixture of gases as composition changes with respect to place.
 Nitrogen found to be 71% and oxygen as 21% and remaining 1% carbon dioxide
along with the 0.03% of other gases.
Oxygen:
Composition: About 21% that is 1/5th of the volume of atmospheric air.
 It is colourless, odourless and tasteless.
 Soluble in water in little extend and heavier than air.
 Supports the combustion.
 Chemically very reactive
Uses of Oxygen:

1. It is used for respiration .
   (a) Plants and animals take up the oxygen for undergoing aerobic respiration to
   generate energy , this is natural way.
   (b) Miners, sea divers , fireman use oxygen cylinders along with mask to breath in
   artificial way.
2. It is use in burning process:
   
3. As oxygen support burning to fuels containing nitrogen , called as oxidation along with
4. liberation of heat , light and carbon dioxide.

3. Medical uses:
   (a)Breathing problems like asthma, pneumonia etc. Are given oxygen from oxygen
   cylinders to enhance the artificial way of respiration.
   (b) Mixture of oxygen and nitrous oxide given to dental patient to render numbness
   on applied area that is anesthetic.
4. Industrial use:
   (a)In the process of welding and cutting
   (b)In rocket it is used as fuel
   (c)In manufacturing of chemicals such as sulphuric acid , nitrous acid.
   Nitrogen :
   Composition: 78-79% , means about 4/5th of the volume of atmospheric air.
   Properties:
    Colourless , odourless and tasteless
    Heavy as air but slight soluble in water.
    Chemically inert or not reactive at low temperature.
   Uses of Nitrogen:
5. Use in preservation of food as it is inert so packed food’s container can be filled.
6. It is used in manufacturing of ammonia , fertilizers such as urea.
7. It is very good refrigerant.
8. Manufacturing of chemicals , trinitrotoluene explosive and nitroglycerine.
9. It controls the combustion as it act as dilator in case of active oxygen.
10. It is essential in growth of plants as nitrates , requires to form plant proteins.
    Carbon dioxide:
    Composition: 0.02-0.03% by volume
     Properties:
    Colourless , odourless and tasteless
     Heavier about 1.5 times than air
     Slightly acidic in nature
     Chemically reactive

Uses of carbon dioxide:

1. It is widely used in aerated soft drinks
2. It is used as refrigerant as dry ice form.
3. It is use in manufacturing of chemicals like baking soda and baking powder.
4. It is used as fire – extinguisher
5. In case of plant for the process of photosynthesis, plays crucial role.
6. It is contributed role in the global warming as it traps the heat.
   Utility of water vapour:
7. In controlling evaporation as it minimizes the rate of evaporation.
8. It is used in detection of climatic conditions, rain, water dew.
9. It is useful in animal and plant growth as it is part of water cycle.
   Nobel gases contribution is less than 1% in air and they are found to be inert chemically.
   Argon, Xenon, Krypton are the Nobel gases found in air.
   Uses of Inert Gases:
10. Helium is used in weather observational ballons
11. It is used in electrical bulbs to provide environment to filament.
12. Neon as it shines used in advertising boards.
13. Xenon as well as krypton are used in photography.
    Polluting Gases :
     such as sulphur dioxide and oxides of nitrogen causes acid rain and serious
    respiratory problem
     Smoke and dust particle causes respiratory issues but help in formation of cloud.
    When metal and non-metal burns in oxygen it forms an oxide.
    A. Formation of Non-Metallic Oxides:
    Sulphur dioxide formed when sulphur burns with brilliant blue flame.
    Other example includes: formation of carbon dioxide when charcoal burns.
    B. Formation of Metallic Oxides:
    Molten sodium burns brightly with golden yellow flame in oxygen to form sodium
    oxide
    Other example includes: Formation of calcium oxide when calcium burns with brick
    red flame.
    

Combustion:
It is rapid chemical change in which a substances combines with oxygen to release
heat along with light.
Example: candle burns in air to produce light and heat along with liberation of
Carbon dioxide and water vapour.
 Combustion is useful in many ways , as cooking of food is the result.
Rusting:
It is the process in which exclusively iron combines with oxygen in the presence of
moisture to form a reddish brown flaky substances called as rust.
Rust: (Fe2O3.H2O)
 It is destructive and weakens the objects.
 Rusting takes a longer duration of time to form the final product.
 It is form of oxidation process in which no liberation of heat and light take
place.
 Rusting can be prevented by oiling, painting and galvanization.
Air pollution:
The contamination of air with undesirable substances leads to some harmful effects on
living and non-living organism called as Air pollution.
Sources of air pollutions:

1. Volcano eruption leads to liberation of sulphur dioxide , carbon mono oxide along
   with dust.
2. Decay of animals causes the emission of oxides of nitrogens
3. Forest fire result into formation of carbon monoxide, sulphur dioxide and carbon
   dioxide
   In manmade sources,
4. The uses of Automobile exhaust leads to liberation of various pollutants such as
   carbon monoxide , carbon dioxide , nitrogen and lead compounds.
5. Chemical industries and iron –steel industries also generates above mentioned
   pollutants in large extent.
6. Burning of fuels leads to increase the amount of carbon monoxide , sulphur dioxide
   along with carbon dioxide.
   

Leaking of chlorofluorocarbon from refrigerants, air conditioners and sprays cans causes
ozone layer depletion and global warming.

Acid Rain:
Acid rain is a result of air pollution. When any type of fuel is burnt, lots of different
chemicals are produced.
Power stations, factories and cars all burn fuels which increase polluting gases. These gases
like nitrogen oxides and sulphur dioxide get react with the tiny droplets of water in clouds to
form respective acids.
The rain from these clouds then falls as very weak acid, known as “Acid rain”..

Harmful effects of Acid Rain:
Acidic rain displaces the minerals from soil and such soil is lack in nutrients, reduces the soil
fertility
Water bodies get toxic as heavy metals such as cadmium, lead from soil get dissolved in it.
Because of these aquatic plants and animals get affected.
There are damaging effect seen on buildings, monuments and statues.
Eg. Whiteness of Taj mahal decreases day by day as there is chemical change occurring
there because of sulphuric and nitric acid