Molar mass of sodium thiosulfate (Na₂S₂O₃)

The molar mass of sodium thiosulfate (Na₂S₂O₃) is 158.096539 g/mol, summed from the IUPAC standard atomic weights of Na x 2, S x 2, O x 3.

Mass of sample

Amount of substance

mol

Molar mass

158.096 539g/mol

= Exact Molar mass of sodium thiosulfate

Moles in the sample mass: 0.063 252 492 mol
Mass of that amount of substance: 158.096 54
Molecules in the sample mass: 3.80915e+22

Show the working

Mass of sample = 10
Amount of substance = 1
Molar mass = 22.98976928*2 + 32.06*2 + 15.999*3 = 158.097
Moles in the sample mass = 10 / 158.097 = 0.063 252 5
Mass of that amount of substance = 1 * 158.097 = 158.097
Molecules in the sample mass = 0.063 252 5 * NA = 3.80915e+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 Na₂S₂O₃: 22.98976928 x 2 + 32.06 x 2 + 15.999 x 3 = 158.096539 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	40.557 %
Oxygen (O)	3	15.999	47.997	30.359 %
Sodium (Na)	2	22.98976928	45.979539	29.083 %

Contributions add to the molar mass of 158.096539 g/mol. Atomic weights are the IUPAC 2021 standard values.

Frequently asked

What is the molar mass of sodium thiosulfate?

158.096539 g/mol, for the formula Na₂S₂O₃.

How do you convert grams of sodium thiosulfate to moles?

Divide the mass in grams by 158.096539 g/mol. One gram of sodium thiosulfate is 0.00632525 mol.

How many grams are in one mole of sodium thiosulfate?

158.096539 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.