Molar mass of iron(ii,iii) oxide (Fe₃O₄)

The molar mass of iron(ii,iii) oxide (Fe₃O₄) is 231.531 g/mol, summed from the IUPAC standard atomic weights of Fe x 3, O x 4.

Mass of sample

Amount of substance

mol

Molar mass

231.531g/mol

= Exact Molar mass of iron(ii,iii) oxide

Moles in the sample mass: 0.043 190 761 mol
Mass of that amount of substance: 231.531
Molecules in the sample mass: 2.60101e+22

Show the working

Mass of sample = 10
Amount of substance = 1
Molar mass = 55.845*3 + 15.999*4 = 231.531
Moles in the sample mass = 10 / 231.531 = 0.043 190 8
Mass of that amount of substance = 1 * 231.531 = 231.531
Molecules in the sample mass = 0.043 190 8 * NA = 2.60101e+22

Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.

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The formula

Molar mass = sum over elements of (atomic weight x number of atoms)
For Fe₃O₄: 55.845 x 3 + 15.999 x 4 = 231.531 g/mol
Moles = mass / molar mass; mass = moles x molar mass
Molecules = moles x 6.02214076 x 10^23 (the Avogadro constant, exact by definition)

Molar mass in grams per mole is numerically equal to the molecular mass in daltons, so this figure doubles as the molecular weight.

Atomic weights are the IUPAC 2021 standard values. Several elements have a range rather than a single value because isotope ratios vary between sources; the conventional single value is used here.

Composition by mass

Element	Atoms	Atomic weight	Contribution (g/mol)	Share of mass
Iron (Fe)	3	55.845	167.535	72.36 %
Oxygen (O)	4	15.999	63.996	27.64 %

Contributions add to the molar mass of 231.531 g/mol. Atomic weights are the IUPAC 2021 standard values.

Frequently asked

What is the molar mass of iron(ii,iii) oxide?

231.531 g/mol, for the formula Fe₃O₄.

How do you convert grams of iron(ii,iii) oxide to moles?

Divide the mass in grams by 231.531 g/mol. One gram of iron(ii,iii) oxide is 0.00431908 mol.

How many grams are in one mole of iron(ii,iii) oxide?

231.531 g, by definition of the molar mass.

Is molar mass the same as molecular weight?

Numerically yes, for the purposes of this calculation. Molecular weight is a dimensionless ratio and molar mass carries units of g/mol, but the digits are identical.

Where the numbers come from

IUPAC 2021 standard atomic weights; Avogadro constant fixed by the 2019 SI.