Molar mass of potassium carbonate (K₂CO₃)

The molar mass of potassium carbonate (K₂CO₃) is 138.2046 g/mol, summed from the IUPAC standard atomic weights of K x 2, C, O x 3.

Mass of sample

Amount of substance

mol

Molar mass

138.2046g/mol

= Exact Molar mass of potassium carbonate

Moles in the sample mass: 0.072 356 492 mol
Mass of that amount of substance: 138.2046
Molecules in the sample mass: 4.35741e+22

Show the working

Mass of sample = 10
Amount of substance = 1
Molar mass = 39.0983*2 + 12.011 + 15.999*3 = 138.205
Moles in the sample mass = 10 / 138.205 = 0.072 356 5
Mass of that amount of substance = 1 * 138.205 = 138.205
Molecules in the sample mass = 0.072 356 5 * NA = 4.35741e+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 K₂CO₃: 39.0983 x 2 + 12.011 + 15.999 x 3 = 138.2046 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
Potassium (K)	2	39.0983	78.1966	56.58 %
Oxygen (O)	3	15.999	47.997	34.729 %
Carbon (C)	1	12.011	12.011	8.6907 %

Contributions add to the molar mass of 138.2046 g/mol. Atomic weights are the IUPAC 2021 standard values.

Frequently asked

What is the molar mass of potassium carbonate?

138.2046 g/mol, for the formula K₂CO₃.

How do you convert grams of potassium carbonate to moles?

Divide the mass in grams by 138.2046 g/mol. One gram of potassium carbonate is 0.00723565 mol.

How many grams are in one mole of potassium carbonate?

138.2046 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.