How many moles of oxygen atoms are present in 34.8 g of potassium sulfate, K2SO4? (Molar masses: K = 39.1 g/mol, S = 32.1 g/mol, O = 16.0 g/mol)
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Correct answer
D. 0.800 mol
Principle or equation
Moles of compound = mass / molar mass. Multiply by the number of oxygen atoms per formula unit.
Why this answer is correct
Molar mass of K2SO4 = 2(39.1) + 32.1 + 4(16.0) = 174.3 g/mol. Moles = 34.8 / 174.3 = 0.200 mol. Oxygen atoms = 0.200 × 4 = 0.800 mol.
Example
For 0.100 mol of Na2CO3, oxygen atoms = 0.300 mol.
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