Molar mass of chromium(iii) oxide (Cr₂O₃)

The molar mass of chromium(iii) oxide (Cr₂O₃) is 151.9892 g/mol, summed from the IUPAC standard atomic weights of Cr x 2, O x 3.

Mass of sample

Amount of substance

mol

Molar mass

151.9892g/mol

= Exact Molar mass of chromium(iii) oxide

Moles in the sample mass: 0.065 794 149 mol
Mass of that amount of substance: 151.9892
Molecules in the sample mass: 3.96222e+22

Show the working

Mass of sample = 10
Amount of substance = 1
Molar mass = 51.9961*2 + 15.999*3 = 151.989
Moles in the sample mass = 10 / 151.989 = 0.065 794 1
Mass of that amount of substance = 1 * 151.989 = 151.989
Molecules in the sample mass = 0.065 794 1 * NA = 3.96222e+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 Cr₂O₃: 51.9961 x 2 + 15.999 x 3 = 151.9892 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
Chromium (Cr)	2	51.9961	103.9922	68.421 %
Oxygen (O)	3	15.999	47.997	31.579 %

Contributions add to the molar mass of 151.9892 g/mol. Atomic weights are the IUPAC 2021 standard values.

Frequently asked

What is the molar mass of chromium(iii) oxide?

151.9892 g/mol, for the formula Cr₂O₃.

How do you convert grams of chromium(iii) oxide to moles?

Divide the mass in grams by 151.9892 g/mol. One gram of chromium(iii) oxide is 0.00657941 mol.

How many grams are in one mole of chromium(iii) oxide?

151.9892 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.