Fundamental L.39

[Lena Jabourian 1C]

Question: A 1.50g sample of metallic tin was placed in a 26.45g crucible and heated until all the tin had reacted with oxygen in air to form an oxide. The crucible and product together were found to weigh 28.35g.

I know that the mass of oxygen would be 0.4g and we need to convert that to moles by dividing by molar mass, I'm just confused how we would know when it's just O vs. O2. So how would we know we need to divide by 16g/mol vs 2(16g/mol), especially since it says oxygen in the air in the problem.

[Emily Nguyen 2D]

Hi Lena!
Usually I would just assume that oxygen in air is referring to O2 due to how atmospheric oxygen is usually present in the O2 molecule. I believe when the wording is "oxide" then they are referring to just O, but I am not sure as well and would love some clarification!