# When do I use the molar mass of diatomic oxygen instead of atomic oxygen in stoichiometry problems?

## To solve the problem below, I used $\text{1 mol O = 16 g O}$ and got the right answer. A white powder is analyzed and found to contain 43.64% phosphorus and 56.36% oxygen by mass. The compound has a molar mass of $\text{283.88 g/mol}$. What are the compound’s empirical and molecular formulas? In what context would I use ${\text{1 mol O"_2 = "32 g O}}_{2}$?

You answered your own question: the compound was found to contain oxygen and phosphorus atoms, not ${O}_{2}$.
${O}_{2}$ and oxygen atoms are different things.