What is the mass of nitrogen atoms in 0.300 mol of ammonium nitrate, NH4NO3? (Molar masses: N = 14.0 g/mol, H = 1.0 g/mol, O = 16.0 g/mol)
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Correct answer
B. 8.40 g
Principle or equation
The mass of a specified element in a compound is calculated by multiplying the amount of the compound by the number of atoms of that element per formula unit and then by the molar mass of the element.
Why this answer is correct
Each formula unit of NH4NO3 contains 2 nitrogen atoms. Therefore, moles of N = 0.300 mol × 2 = 0.600 mol. Mass of N = 0.600 mol × 14.0 g/mol = 8.40 g.
Example
For a compound with 3 oxygen atoms per formula unit, 0.200 mol contains 0.600 mol O atoms; mass = 0.600 × 16.0 = 9.60 g.
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