Molar mass of pyrite (FeS₂)

The molar mass of pyrite (FeS₂) is 119.965 g/mol, summed from the IUPAC standard atomic weights of Fe, S x 2.

Mass of sample

Amount of substance

mol

Molar mass

119.965g/mol

= Exact Molar mass of pyrite

Moles in the sample mass: 0.083 357 646 mol
Mass of that amount of substance: 119.965
Molecules in the sample mass: 5.01991e+22

Show the working

Mass of sample = 10
Amount of substance = 1
Molar mass = 55.845 + 32.06*2 = 119.965
Moles in the sample mass = 10 / 119.965 = 0.083 357 6
Mass of that amount of substance = 1 * 119.965 = 119.965
Molecules in the sample mass = 0.083 357 6 * NA = 5.01991e+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 FeS₂: 55.845 + 32.06 x 2 = 119.965 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
Sulfur (S)	2	32.06	64.12	53.449 %
Iron (Fe)	1	55.845	55.845	46.551 %

Contributions add to the molar mass of 119.965 g/mol. Atomic weights are the IUPAC 2021 standard values.

Frequently asked

What is the molar mass of pyrite?

119.965 g/mol, for the formula FeS₂.

How do you convert grams of pyrite to moles?

Divide the mass in grams by 119.965 g/mol. One gram of pyrite is 0.00833576 mol.

How many grams are in one mole of pyrite?

119.965 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.