Molar mass of aluminium sulfate (Al₂(SO₄)₃)

The molar mass of aluminium sulfate (Al₂(SO₄)₃) is 342.131077 g/mol, summed from the IUPAC standard atomic weights of Al x 2, S x 3, O x 12.

Mass of sample

Amount of substance

mol

Molar mass

342.131 077g/mol

= Exact Molar mass of aluminium sulfate

Moles in the sample mass: 0.029 228 564 mol
Mass of that amount of substance: 342.131 08
Molecules in the sample mass: 1.76019e+22

Show the working

Mass of sample = 10
Amount of substance = 1
Molar mass = 26.9815384*2 + 32.06*3 + 15.999*12 = 342.131
Moles in the sample mass = 10 / 342.131 = 0.029 228 6
Mass of that amount of substance = 1 * 342.131 = 342.131
Molecules in the sample mass = 0.029 228 6 * NA = 1.76019e+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 Al₂(SO₄)₃: 26.9815384 x 2 + 32.06 x 3 + 15.999 x 12 = 342.131077 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)	12	15.999	191.988	56.115 %
Sulfur (S)	3	32.06	96.18	28.112 %
Aluminium (Al)	2	26.9815384	53.963077	15.773 %

Contributions add to the molar mass of 342.131077 g/mol. Atomic weights are the IUPAC 2021 standard values.

Frequently asked

What is the molar mass of aluminium sulfate?

342.131077 g/mol, for the formula Al₂(SO₄)₃.

How do you convert grams of aluminium sulfate to moles?

Divide the mass in grams by 342.131077 g/mol. One gram of aluminium sulfate is 0.00292286 mol.

How many grams are in one mole of aluminium sulfate?

342.131077 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.