(a) draw a diagram to show the process of obtaining constituent gases from air
(b)which gas will condense first ?why?
Separation of gases by fractional distillation
Air is a homogeneous mixture of different gases such as oxygen, nitrogen, carbon dioxide, etc. You must have observed oxygen cylinders in hospitals and cylinders of carbon dioxide in cars and buildings. These cylinders are prepared by separating individual gases from the air.
Separation of the components of air:
- Air is first filtered to remove dust particles. Then, it is compressed under high pressure.
- This compressed air is then passed through a water condenser to decrease its temperature.
- The cold compressed air is now passed through a separator. Here, carbon dioxide separates as dry ice (solid carbon dioxide). Due to repeated compression, air becomes cold that turns into liquid.
- The liquid air coming out of the separator is passed through an expansion jet into the distillation column. Here, it is warmed slowly. Liquid nitrogen, having the lowest boiling point of –196°C, boils to form liquid nitrogen gas. This gas is collected from the upper part of the column. Argon, having a boiling point of
–186°C, is collected next. Oxygen, having a higher boiling point of –183°C, is collected last.