How to determine the %age of oxygen in the air by volume involving reactions of copper, iron and phosphorous?

I need to be able to describe how experiments involving reactions of elements such as copper, iron and phosphorous with air can be used to determine the percentage by volume of oxygen in the air.


Need your guys help. haha thanks :)How to determine the %age of oxygen in the air by volume involving reactions of copper, iron and phosphorous?
There is no such element as 'phosphorous' in your question .. I presume you mean phosphorus?





For using copper, get two ground glass 100ml lab syringes. Set one at 100ml, the other at zero. Connect them both to a 20cm length of pyrex glass tube filled with freshly reduced wire form copper, held in place with a little glass wool at each end. Heat the copper gently while drawing the air from one syringe to another. Continue until there are no further changes. Allow to cool a little. Draw gas into one syringe, read volume. eg final vol =79cm3, so percent O2 = 100-79 =21%





For iron, get a 125 x 16mm test tube and wet the inside. Sprinkle in iron filings so they stick to the side. Invert over water and leave several days. O2 in damp air reacts, can see rust and water level rises by about a fifth. Tube difficult to clean afterwards!





Phosphorus. Set up a large bell jar in a trough of water. The bell jar should have a rubber stopped top. Put a few pieces of white phosphorus in an evaporating basin floating in the trough, and cover with the bell jar, stopper removed. Mark water level with a stabilo pencil or similar. Just warm the end of a long glass rod in a bunsen and lower it through the top of the bell jar and just touch the white phosphorus in the dish. It will catch fire. Remove rod and put in bung firmly. When reaction has finished, allow to cool and note new water level. By finding both start and finish volumes, the percentage of O2 in air is easily calculated. Note vital safety precautions are needed with white phosphorus, which is both toxic and dangerous.





I have had chemistry classes using all three of the above methods, but the copper one is both quick, easy, and accurate.