4 This question is about rusting.
(a) When iron rusts, it-reacts with oxygen in the air.
A student uses the rusting of iron to find the percentage of oxygen in a sample of air.
The diagram shows the apparatus.
100 80 60 40 20
cm
air
gas syringe
conical flask
wet iron
filings
These are the student's results.
volume of air in conical flask and connecting tube = 265 cm
volume of air in gas syringe at start = 100 cm
volume of air in gas syringe at end = 25 cm
Calculate the percentage of oxygen in the sample of air using the student's results.
(3)​