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1.The air is first filtered to remove dust, then water vapour and carbon dioxide are removed (If water vapour and carbon dioxide are not removed, they would become solid in the cooling process and block the pipes).
2.Air is compressed to a high pressure and then cooled. This cooled air is then allowed to expand quickly into a chamber through a jet. This expansion cools the air even more.
3.The process of compression, cooling and rapid expansion of air is repeated again and again making the air more and more cool. Ultimately the air gets so cooled that it turns into a liquid. In this way,liquid air is obtained.
4.The liquid air is fed into a tall fractional distillation column from near its bottom and warmed up slowly.
(a) Liquid nitrogen (present in liquid air) has the lowest boiling point of, -196°.So, on warming,liquid nitrogen boils off first to form nitrogen gas. This nitrogen gas is collected from the top part of the fractional distillation column.
(b) Liquid argon (present in liquid air) has a slightly higher boiling point of, -186° So, liquid argon boils off next and collected as argon gas in the middle part of the fractional distillation column.
(c) Liquid oxygen (present in liquid air) has a still higher boiling point of, -183°.So, liquid oxygen boils off last and collected as oxygen gas from the bottom of the fractional distillation column.
A flow diagram showing the main processes involved in obtaining different gases from air is given below :
Notes
Matter in Our Surroundings - Notes
1. 7. Metals are Solids at the Room Temperature
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6. 3. Non-Metals are Bad Conductors of Heat and Electricity.
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8. 11. Non-Metals Have Many Different Colours.
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9. 7. Non-Metals may be Solid, Liquid or Gases at the Room Temperature.
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16. 8. Metals Generally Have High Melting Points and Boiling Points.
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19. 8. Non-Metals Have Comparatively Low Melting Points and Boiling Points
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23. To Study the Properties of a Suspension
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24. Effect of Temperature and Pressure on Solubility
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25. Chemical Formula for daily use material
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26. 1. Non-Metals are Not Malleable. Non-Metals are Brittle.
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28. Pure Substances : Elements and Compounds
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30. Solutions, Suspensions And Colloids
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35. 1. Separation by a Suitable Solvent
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42. 3. Metals are Good Conductors of Heat and Electricity.
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46. To Separate the Salt-Water Mixture (or Salt-Solution)
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47. 4. Non-Metals are Not Lustrous (Not Shiny). They are Dull in Appearance.
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49. To Study the Properties of a Compound of Iron and Sulphur
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