Separating gases in the atmosphere Flashcards
What gases is the atmosphere mainly comprised of?
Nitrogen and oxygen
What are the percentages of different gases in the atmosphere?
Nitrogen - 78%
Oxygen - 20%
Carbon dioxide, argon, helium, all other gases - 2%
How can the gases in the atmosphere be separated?
We can use the different boiling points of the gases to separate them out by condensing them and then separating them through fractional distillation, if they have not frozen.
Describe the process of liquefying the air.
Air is filtered to remove dust, and then cooled in stages until it reaches –200°C. At this temperature it is a liquid. We say that the air has been liquefied.
What happens as the air liquefies? (4)
Water vapour condenses, and is removed using absorbent filters
Carbon dioxide freezes at –79ºC, and is removed Oxygen liquefies at –183ºC
Nitrogen liquefies at –196ºC
The liquid oxygen and nitrogen are then separated by fractional distillation.
Describe the process of fractional distillation to separate the gases in the atmosphere. (6)
The liquefied air is passed into the bottom of a fractionating column. Just as in the columns used to separate oil fractions, the column is warmer at the bottom than it is at the top.
The liquid nitrogen boils at the bottom of the column. Gaseous nitrogen rises to the top, where it is piped off and stored.
Liquid oxygen collects at the bottom of the column. The boiling point of argon - the noble gas that forms 0.9 percent of the air - is close to the boiling point of oxygen, so a second fractionating column is often used to separate the argon from the oxygen.
What are some uses of nitrogen and oxygen after they have been separated? (4)
Liquid nitrogen is used to freeze food
Food is packaged in gaseous nitrogen to increase its shelf life
Oil tankers are flushed with gaseous nitrogen to reduce the chance of explosion
Oxygen is used in the manufacture of steel and in medicine.
