What is the mass of oxygen atoms in 0.250 mol of magnesium nitrate, Mg(NO3)2? (Molar masses: Mg = 24.3 g/mol, N = 14.0 g/mol, O = 16.0 g/mol)
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Correct answer
A. 24.0 g
Principle or equation
Each formula unit of Mg(NO3)2 contains 6 oxygen atoms. Moles of O = 6 × moles of compound. Mass = moles × molar mass.
Why this answer is correct
Moles of O = 0.250 mol × 6 = 1.50 mol. Mass of O = 1.50 mol × 16.0 g/mol = 24.0 g.
Example
For 0.100 mol Ca(NO3)2, O moles = 0.600, mass = 9.6 g.
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