Final answer:
The mass of oxygen that reacted with the iron to form iron oxide is 6.5 grams, calculated by subtracting the mass of iron from the mass of the formed rust.
Step-by-step explanation:
To find how much oxygen reacted with iron to form iron oxide, a mass difference calculation is required. Given that the mass of iron before the reaction is 25.0 g and the mass of iron oxide after the reaction is 31.5 g, the mass of oxygen that reacted can be determined by subtracting the mass of iron from the mass of iron oxide.
The mass of oxygen that reacted with the iron to form iron oxide is 6.5 g.
When a chemical reaction occurs between iron and oxygen, iron oxide or rust is formed. In this scenario, the initial mass of iron is given as 25.0 g. After the reaction has taken place, the resulting substance is iron oxide, which has a combined mass of 31.5 g. To calculate the mass of oxygen that has combined with the iron, one needs to subtract the mass of iron from the total mass of the iron oxide formed. Thus, the calculation would be 31.5 g (iron oxide) - 25.0 g (iron) = 6.5 g.
This result represents the mass of oxygen that has reacted with the iron to produce the iron oxide. Rust formation involves the oxidation of iron in the presence of moisture and oxygen, leading to the iron(III) oxide hydrate. The stoichiometry of the reaction between iron and oxygen is based on the chemical equation provided, but in this case, we only need the mass difference to answer the student's question.