Oxygen Is (Roughly) 20% Of Dry Air…

I do love a snappy post title!

Air contains lots of moisture. It can be as much as 30 g of water in every 1 m³ of air. If you dry the air (by passing it over a chemical that reacts with water) then the mixture remaining is slightly more than 20% oxygen. You can demonstrate that this is the case with a simple experiment that uses the rusting of iron.

Set up a boiling tube with some wet iron wool stuffed into the base. This can be placed upside down into 20 cm³ of water in a beaker. To know how much air is in the tube, measure the distance χ from the surface of the water to the end of the tube. After a day or so, the iron should have rusted and the water level will have risen in the tube to replace the oxygen that has reacted. Measure the new length ϒ. You should find that the column of air has reduced by about 20%.

Question…

1. Name a chemical that could be used to remove the water from air.
2. What difference in the wire wool should you observe after a week?
3. Why must the iron wool be damp for this to work effectively?
4. What is the percentage of nitrogen in the air?
5. What piece of equipment would you use to measure the volume of water held in a test tube?