Final answer:
1 mol of ethanol (C₂H₆O) and 1 mol of butan-1-ol (C₄H₁₀O) each have one mole of oxygen atoms. Molecular mass and molar mass both reflect the mass of a compound's components, expressed differently in units; molecular mass in atomic mass units and molar mass in grams per mole.
Step-by-step explanation:
The substances that have the same number of oxygen atoms are C₂H₆O (ethanol) and C₄H₁₀O (butan-1-ol). Each of these substances contains one mole of oxygen atoms per mole of the compound. Comparatively, 1 mol of ethanol (C₂H₆O) contains one mole of oxygen atoms, as does 1 mol of butan-1-ol (C₄H₁₀O), while C₈H₁₈ (octane) and CH₃CH₂Br (bromoethane) do not contain any oxygen atoms.
To determine which substance contains the greatest number of moles of oxygen atoms, we must look at the molecular composition of each compound. Ethanol (C₂H₅OH) has one oxygen per molecule, formic acid (HCO₂H) has two, and water (H₂O) has one.
Molecular mass and molar mass are related concepts; both are a measure of the mass of a compound. The molecular mass is the sum of the atomic masses of all atoms in a molecule and is expressed in atomic mass units (amu), while the molar mass is the mass of one mole of that substance and is expressed in grams per mole (g/mol). They differ in that molecular mass is a relative measure at the molecular scale, and molar mass relates to the mass of a substance in bulk quantities.