If you have 8.04 g of oxygen with a molar mass of 16.00 g/mol, how many moles do you have?

• A. 0.250 mol
• B. 0.5025 mol
• C. 0.404 mol
• D. 0.125 mol

Answer: (B)

Calculating how much of a substance you have in moles uses the relationship moles = mass ÷ molar mass. Here, you’re given 8.04 g of oxygen and a molar mass of 16.00 g per mole. Divide: 8.04 g ÷ 16.00 g/mol = 0.5025 mol. So you have about 0.5025 moles of oxygen. In practice you’d report with appropriate significant figures (0.503 mol), but the calculation shows the correct amount in moles.