Molar mass of phosphoric acid (H₃PO₄)

The molar mass of phosphoric acid (H₃PO₄) is 97.993762 g/mol, summed from the IUPAC standard atomic weights of H x 3, P, O x 4.

Mass of sample

Amount of substance

mol

Molar mass

97.993 762g/mol

= Exact Molar mass of phosphoric acid

Moles in the sample mass: 0.102 047 31 mol
Mass of that amount of substance: 97.993 762
Molecules in the sample mass: 6.14543e+22

Show the working

Mass of sample = 10
Amount of substance = 1
Molar mass = 1.008*3 + 30.973761998 + 15.999*4 = 97.9938
Moles in the sample mass = 10 / 97.9938 = 0.102 047
Mass of that amount of substance = 1 * 97.9938 = 97.9938
Molecules in the sample mass = 0.102 047 * NA = 6.14543e+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 H₃PO₄: 1.008 x 3 + 30.973761998 + 15.999 x 4 = 97.993762 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	65.306 %
Phosphorus (P)	1	30.973761998	30.973762	31.608 %
Hydrogen (H)	3	1.008	3.024	3.0859 %

Contributions add to the molar mass of 97.993762 g/mol. Atomic weights are the IUPAC 2021 standard values.

Frequently asked

What is the molar mass of phosphoric acid?

97.993762 g/mol, for the formula H₃PO₄.

How do you convert grams of phosphoric acid to moles?

Divide the mass in grams by 97.993762 g/mol. One gram of phosphoric acid is 0.0102047 mol.

How many grams are in one mole of phosphoric acid?

97.993762 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.