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Determination of percentage of air used up in rusting.

Answer Text:
Determination of percentage of air used up in rusting.
Apparatus:
- Gas jar;
- Trough;
- Beehive;
- Iron fillings//powder
Procedure:
- The gas jar is divided into five equal portions by marking around it using a waterproof marker;
- The gas jar is wet near the bottom and some iron fillings sprinkled on it;
- Some water is put in a trough and the jar with iron fillings // wool // powder inverted over it;
- The initial colour of iron fillings is noted;
- The set -up is left undisturbed for a few days until the water shows no further change in rising;
Diagrams of apparatus set up:

Observations:
- The iron fillings change colour from a grey to form a brown solid;
- Water level in the gas jar rises // increases until the first mark in the gas jar;
- The water level in the trough decreases;
Explanations:
- The gas jar is moistened to make the iron fillings stick onto its surface so that the fillings do not fall in the water when the gas jar is inverted;
- The brown substance formed is called rust and its chemical name is hydrated iron (III) oxide;
- During rusting, oxygen is utilized, thus creating a partial vacuum in the gas jar;
- This causes the water level in the gas jar to rise up and the water level in the trough to go down;
- The rise in water level is equivalent to about 1/5 of the original air volume, which translates to about 20%;
Conclusion:
- When rusting occurs about 20% of air, which is oxygen, is used up;