Molar mass of forsterite olivine (Mg₂SiO₄)

The molar mass of forsterite olivine (Mg₂SiO₄) is 140.691 g/mol, summed from the IUPAC standard atomic weights of Mg x 2, Si, O x 4.

Mass of sample

Amount of substance

mol

Molar mass

140.691g/mol

= Exact Molar mass of forsterite olivine

Moles in the sample mass: 0.071 077 752 mol
Mass of that amount of substance: 140.691
Molecules in the sample mass: 4.2804e+22

Show the working

Mass of sample = 10
Amount of substance = 1
Molar mass = 24.305*2 + 28.085 + 15.999*4 = 140.691
Moles in the sample mass = 10 / 140.691 = 0.071 077 8
Mass of that amount of substance = 1 * 140.691 = 140.691
Molecules in the sample mass = 0.071 077 8 * NA = 4.2804e+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 Mg₂SiO₄: 24.305 x 2 + 28.085 + 15.999 x 4 = 140.691 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
Oxygen (O)	4	15.999	63.996	45.487 %
Magnesium (Mg)	2	24.305	48.61	34.551 %
Silicon (Si)	1	28.085	28.085	19.962 %

Contributions add to the molar mass of 140.691 g/mol. Atomic weights are the IUPAC 2021 standard values.

Frequently asked

What is the molar mass of forsterite olivine?

140.691 g/mol, for the formula Mg₂SiO₄.

How do you convert grams of forsterite olivine to moles?

Divide the mass in grams by 140.691 g/mol. One gram of forsterite olivine is 0.00710778 mol.

How many grams are in one mole of forsterite olivine?

140.691 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.