National League for Nursing (NLN PAX) Practice Exam

What best explains the increase in mass when steel wool burns?

1. The iron oxide formed has more mass than the iron alone

2. The oxygen from the air combines with the iron

3. The ash produced weighs more than the original iron

4. The heat causes expansion and increased mass

The correct answer is: The iron oxide formed has more mass than the iron alone

The increase in mass when steel wool burns is best explained by the fact that oxygen from the air reacts with the iron present in the steel wool to form iron oxide. This chemical reaction involves the iron atoms combining with oxygen atoms, resulting in a compound that has more mass than the original iron alone because it adds the mass of the oxygen that is now part of the compound. In a combustion reaction like this, the mass of the reactants (iron and oxygen) equals the mass of the products (iron oxide) due to the law of conservation of mass. This means that while the structure of the material changes during the combustion process, its total mass reflects all the elements involved in the chemical reaction. Thus, the presence of oxygen is critical to the formation of the heavier iron oxide, which accounts for the perceived increase in mass.