What is the mass of oxygen atoms in 0.200 mol of phosphoric acid, H3PO4? (Molar masses: H = 1.0 g/mol, P = 31.0 g/mol, O = 16.0 g/mol)
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Correct answer
C. 12.8 g
Principle or equation
Each mole of H3PO4 contains 4 moles of O atoms. Mass = moles × molar mass.
Why this answer is correct
Moles of O = 0.200 mol × 4 = 0.800 mol. Mass of O = 0.800 mol × 16.0 g/mol = 12.8 g.
Example
For 0.100 mol H2SO4, moles of O = 0.400 mol, mass = 6.40 g.
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