A researcher sets up an experiment to determine the percentage of oxygen in a localized air sample. The apparatus consists of a sealed reaction vessel of volume 125 cm3125\text{ cm}^3125 cm3 containing an excess of moist iron wool. This vessel is connected via a narrow tube of negligible volume to a gas syringe.
At the start of the experiment, the gas syringe is filled with air and reads 85 cm385\text{ cm}^385 cm3.
The system is left for several days to allow the iron wool to fully rust, consuming all the oxygen inside. After the volume has ceased to change, the final reading on the gas syringe is recorded as 42 cm342\text{ cm}^342 cm3.
Calculate the volume of oxygen consumed during the reaction in cm3\text{cm}^3cm3.
Calculate the total initial volume of air in the closed system in cm3\text{cm}^3cm3.
Use your answers to parts (a) and (b) to calculate the percentage of oxygen in this air sample. Give your answer to one decimal place.
10 exam-style questions on Edexcel IGCSE Chemistry Gases in the atmosphere. Each one has a worked solution and a mark scheme showing where the marks go.