O Levels Chemistry (5070)•5070/11/M/J/19
Explanation
Mass Percent of Nitrogen in NH₄NO₃ Steps:
- Calculate molar mass of NH₄NO₃: 2N (14×2=28) + 4H (1×4=4) + 3O (16×3=48) = 80 g/mol.
- Mass of nitrogen: 14 g/mol × 2 atoms = 28 g/mol.
- Percentage by mass: (28/80) × 100% = 35%. Why D is correct:
- Mass percent formula (mass of element/molar mass of compound) × 100% gives exactly 35% for nitrogen in NH₄NO₃. Why the others are wrong:
- A: 17.5% is the mass percent of hydrogen, not nitrogen.
- B: 22.2% undercounts nitrogen atoms or misapplies atomic masses.
- C: 33.3% approximates oxygen's percent but ignores nitrogen's full contribution.
Final answer: D
Topic: Relative masses of atoms and molecules
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