A student weighs out 17.4 g of manganese(IV) oxide, MnO2. How many moles of manganese atoms are present in this sample? (Molar masses: Mn = 54.9 g/mol, O = 16.0 g/mol)
Show the answer and explanation
Correct answer
B. 0.200 mol
Principle or equation
The amount of substance in moles is calculated by dividing the mass by the molar mass. The molar mass of MnO2 is the sum of the molar masses of its constituent atoms: 54.9 g/mol + 2 × 16.0 g/mol = 86.9 g/mol. Since each formula unit contains one manganese atom, the moles of manganese atoms equal the moles of MnO2.
Why this answer is correct
Calculate the molar mass of MnO2: 54.9 + 2(16.0) = 86.9 g/mol. Then divide the given mass by the molar mass: 17.4 g ÷ 86.9 g/mol = 0.200 mol. Thus, the sample contains 0.200 mol of MnO2, which corresponds to 0.200 mol of Mn atoms.
Example
For a 43.45 g sample of MnO2, the amount is 43.45 g ÷ 86.9 g/mol = 0.500 mol, so it contains 0.500 mol of Mn atoms.
This published item includes a stored explanation and passed the platform’s publication workflow. It is independent preparation material, not a claim of an official or recalled examination question.