Final answer:
The mass of oxygen used in the reaction to form iron oxide from iron is 1.48 g, calculated by subtracting the mass of iron (19.43 g) from the mass of iron oxide (20.91 g).
Step-by-step explanation:
To find the mass of the oxygen used during the reaction between iron and oxygen to form iron oxide, we can use the given masses of iron and iron oxide. Since the mass of iron is provided as 19.43 g and the mass of iron oxide is given as 20.91 g, we can calculate the mass of oxygen by subtracting the mass of iron from the mass of iron oxide:
Mass of Oxygen = Mass of Iron Oxide - Mass of Iron
Mass of Oxygen = 20.91 g - 19.43 g
Mass of Oxygen = 1.48 g
The mass of the oxygen used is 1.48 g. This answer is to the correct number of significant figures, as the mass values given are to four significant figures and subtraction maintains the least number of decimal places.