# Estimate the amount of oxygen in air

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A series of free IGCSE Chemistry Activities and Experiments (Cambridge IGCSE Chemistry).

Method:
1. Place some copper in a horizontal silica tube, between two syringes. There must be no gaps between the syringes and the tube unless a three-way stopcock is fitted.
2. Fill in the ends of the combustion tube with short pieces of hard-glass rod which are slightly smaller in diameter than the inside diameter of the tube, and fill one syringe with 100 cm3 of air.
3. Test the apparatus for airtightness by pushing the air from one syringe to the other and back.
4. Heat the copper fairly vigorously and, when hot, move the syringe plungers slowly backwards and forwards while the heating is continued.
5. After about 2 minutes, stop the heating and cool the combustion tube with a damp cloth. Note the volume reading on the syringe.
6. Repeat the heating of the copper for a further minute, cool as before, and continue this procedure until the volume reading is constant.
7. The volume occupied by the active part of the air is the difference between the first and the final volume readings. From these two volumes the percentage of the active part of the air can be calculated.

Estimate the amount of oxygen in earth's atmosphere

This is a demonstration of the reduction in volume when air is passed over heated copper.
100cm3 of air are passed from one gas syringe to another through a horizontal narrow silica tube.
Some copper (freshly reducing wire-form copper(II) oxide) is contained in the tube and heated strongly.

Practical points:
Test for airtightness before heating

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