A student sets up an apparatus to measure the percentage of oxygen in a sample of air using the rusting of wet iron filings in a closed system.
The apparatus consists of a 110 cm3 conical flask containing an excess of wet iron filings, connected by a tube of negligible volume to a gas syringe.
At the start of the experiment, the reading on the syringe is 75 cm3.
The apparatus is left for one week for the reaction to run to completion. At the end of the experiment, the reading on the syringe is 36 cm3.
Calculate the volume of oxygen used up during the experiment in cm3\text{cm}^3cm3.
Calculate the total volume of air in the apparatus at the start of the experiment in cm3\text{cm}^3cm3.
Use your answers to (a) and (b) to calculate the percentage of oxygen in this air sample. Give your answer to one decimal place.
