Useful Products From Air…

The general consensus on the Internet is that oxygen is fractionally less then 21% of dry air. I normally teach 20% because that is one fifth (which is pleasing) and allows a whole percent for argon. Consensus again puts argon at about 0.9% with carbon dioxide occupying a steadily increasing value just below 0.04%. Nitrogen is widely described as 78% so I am at least right on one out of the big three. In my defence, I have only been trying to make it easier to remember, rather than deliberately leading you astray. The data refer to dry air because the humidity (or water vapour content) of air can vary considerably. Leaving out water allows for an easier comparison.

Air is one of my top five naturally occurring mixtures. We can use it just as it is, e.g. for breathing, or we can separate it out into its component parts. Nitrogen, oxygen and argon all have industrial uses. Nitrogen is a very important raw material, e.g. for making fertiliser or in liquid form it is a very useful coolant. Oxygen is useful in hospitals for people with respiratory problems or is used to make things burn hotter, e.g. welding torches. Argon is inert so it can be used as a storage atmosphere for highly reactive materials, e.g. the Group I metals.

Air is separated into its different components by fractional distillation. It is first filtered and then cooled to remove unwanted gases. Then it is pressurised and cooled some more until it turns into a liquid. Since nitrogen has a lower boiling point than oxygen, it can be evaporated away whilst the oxygen remains liquid. The following video is a corporate publicity video but it does take you through the process in some detail – starting simply and increasing in complexity as it goes.

Questions…

1. In salt solution, what is the solute and what is the solvent?
2. How would you separate the salt from salt solution?
3. Before separation, air is passed through filters. What does this remove?
4. Initial cooling of the air removes carbon dioxide, water and hydrocarbons. Suggest a hydrocarbon that might be in air.
5. What harmful effect is increasing CO₂ in the atmosphere having?
6. To what group on the periodic table does argon belong, and as what are the members collectively known?
7. What is the boiling point of nitrogen?
8. What might be another ‘naturally occurring mixture’?