How many moles of oxygen atoms are present in 11.0 g of carbon dioxide (CO2)? (Molar masses: C = 12.0 g/mol, O = 16.0 g/mol)
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Correct answer
B. 0.50 mol
Principle or equation
The amount of substance is mass divided by molar mass. The number of atoms of an element in a compound equals the number of moles of the compound multiplied by the number of atoms of that element per formula unit.
Why this answer is correct
Molar mass of CO2 = 12.0 + 2(16.0) = 44.0 g/mol. Moles of CO2 = 11.0 g / 44.0 g/mol = 0.25 mol. Each CO2 molecule contains 2 oxygen atoms, so moles of O atoms = 2 × 0.25 = 0.50 mol.
Example
For 22.0 g CO2, moles CO2 = 0.50 mol, O atoms = 1.0 mol.
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