Question

(d) why will the crucible and its contents gain mass as a result of heating the mg in air?

Explanation:

When magnesium (\(Mg\)) is heated in air, it reacts with oxygen (\(O_2\)) in the air. The chemical reaction is \(2Mg + O_2\xrightarrow{\Delta}2MgO\). According to the law of conservation of mass, the mass of the reactants (\(Mg\) and \(O_2\)) is equal to the mass of the products (\(MgO\)). Since oxygen from the air (which was not initially part of the contents of the crucible) combines with magnesium to form magnesium oxide (\(MgO\)), the total mass of the crucible and its contents increases.

Answer:

Because magnesium reacts with oxygen in the air to form magnesium oxide, and the mass of oxygen (from the air) that combines with magnesium is added to the mass of the original magnesium (in the crucible), resulting in a gain in mass of the crucible and its contents.