GCSE CHEMISTRY - COMPOUNDS AND MIXTURES - LESSON 8 - fractional distillation of air

Summary

This lesson explains the process of separating the components of air through fractional distillation, a physical process. Air is first filtered to remove dust, then cooled to condense water vapor, and treated to remove carbon dioxide as dry ice. The air is then liquefied at -200°C, and gases like nitrogen, oxygen, and argon are separated based on their boiling points. Nitrogen evaporates first, followed by oxygen and a small amount of argon. The process results in the separation of pure nitrogen, oxygen, and argon, with practical industrial applications for each gas.

Takeaways

• 😀 Air is a mixture, and separating its components involves physical processes like fractional distillation.
• 😀 The main components of air are nitrogen (78%), oxygen (21%), and argon (0.9%), with other gases making up the remaining 0.1%.
• 😀 Water vapor is also present in air, but its percentage varies depending on location and time.
• 😀 Fractional distillation of air begins with filtering to remove dust particles.
• 😀 After filtering, the air is cooled, causing water vapor to condense and be removed using absorbing filters.
• 😀 At temperatures of around minus 79°C, carbon dioxide is removed from the air and collected as dry ice.
• 😀 The air is then compressed and further cooled to minus 200°C, causing it to become liquid (referred to as liquid air).
• 😀 Liquid air is passed through a fractionating column where nitrogen evaporates first due to its low boiling point (-196°C).
• 😀 Nitrogen is separated from the mixture and stored under pressure, while oxygen and argon remain at the bottom of the tower.
• 😀 Oxygen and a small amount of argon are removed in their liquid state, with oxygen being treated as a relatively pure gas for further use.
• 😀 Argon is a noble gas and remains inert, not reacting with other substances during the separation process.

Q & A

What is air composed of, and what is the approximate percentage of each component?

Air is composed mainly of nitrogen (78%), oxygen (21%), and argon (0.9%), with the remaining 0.1% consisting of minor gases. Water vapor is also present but varies depending on the location and conditions.

What is fractional distillation, and why is it used to separate air components?

Fractional distillation is a physical process used to separate components of a mixture based on differences in their boiling points. It is used to separate the gases in air, as air is a mixture of gases with distinct boiling points.

What happens to air as it enters the fractional distillation process?

Air is first filtered to remove dust, then cooled, causing water vapor to condense and be removed before the air passes into refrigeration tanks.

At what temperature does carbon dioxide freeze during the distillation process?

Carbon dioxide freezes at approximately -78°C, forming dry ice, which is then removed from the air during the distillation process.

What is the role of the refrigeration tank in the fractional distillation process?

The refrigeration tank cools the air to -79°C, causing water vapor to condense and carbon dioxide to freeze, which are then removed before further distillation steps.

What happens to the air once it reaches -200°C in the fractional distillation process?

At -200°C, the air becomes liquid, and nitrogen, oxygen, and argon condense into liquid form. The liquid air is then directed into a fractionating column for further separation.

How does fractional distillation separate nitrogen, oxygen, and argon from liquid air?

As the liquid air warms up in the fractionating column, nitrogen, with the lowest boiling point of -196°C, evaporates first and rises to the top. Oxygen and argon remain at the bottom of the column in liquid form.

What happens to the nitrogen that evaporates first in the distillation column?

Nitrogen, once evaporated, rises to the top of the fractionating column and is collected and stored under pressure.

Why is argon considered an inert gas, and how is it handled during the distillation process?

Argon is a noble gas, meaning it does not react with other substances. During the distillation process, it remains in liquid form at the bottom of the column and is usually left mixed with oxygen.

What happens to the oxygen after the distillation process?

After the distillation, oxygen is collected and treated as a nearly pure gas, as it is separated from other components, mainly argon.