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The ratio of the unit mass of a molecule of nitrogen (N ₂ ) to that of an oxygen molecule (O ₂ ) is approximately:
8 : 7
7 : 8
14 : 32
28 : 16
7 : 8
The mass of a molecule is determined by its molecular weight, calculated as the sum of atomic masses of the atoms present in one molecule. For N2, the molecular mass is 2×14=28 u, and for O2, it is 2×16=32 u; hence, the ratio is 28:32, which simplifies to 7:8.
The mass of a molecule is determined by its molecular weight, calculated as the sum of atomic masses of the atoms present in one molecule. For N2, the molecular mass is 2×14=28 u, and for O2, it is 2×16=32 u; hence, the ratio is 28:32, which simplifies to 7:8.
Think of it like comparing the weight of two boxes: one filled with two apples (Nitrogen atoms) and the other with two slightly heavier oranges (Oxygen atoms), where the ratio of their weights remains proportional to the individual weights of the fruits.
MN2=2×14=28 g/mol — Molar mass of Nitrogen
MO2=2×16=32 g/mol — Molar mass of Oxygen
Ratio=3228=87 — Simplifying the mass ratio
According to Dalton's atomic theory and Avogadro's law, the molar mass of an element or compound represents the mass of 6.022×1023 particles. Since we are comparing the ratio of masses of single molecules, the Avogadro constant cancels out, leaving the ratio of the molecular weights as the direct comparison of mass.
Atomic mass of Nitrogen (N) is approximately 14 u.
Atomic mass of Oxygen (O) is approximately 16 u.
Molecular mass is the sum of the atomic masses of all atoms in the molecule.
Stoichiometric calculations in chemical reactions.
Determining vapor density of gases relative to each other.
| Feature | Nitrogen (N_2) | Oxygen (O_2) |
|---|---|---|
Molecular Data | 28 u | 32 u |
Nitrogen gas (N2) comprises about 78% of Earth's atmosphere.
Oxygen gas (O2) is essential for respiration and comprises about 21% of the atmosphere.
Option D (28:16) incorrectly uses the atomic mass of Oxygen instead of the molecular mass of O2.
B is correct — The ratio of the molecular masses of N2 (28) and O2 (32) simplifies to 7:8.
Always ensure you consider the atomicity of the gas (e.g., N2 and O2 are diatomic) before calculating mass ratios, as ignoring the subscript will lead to incorrect answers.
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